Django DOC of Model reference

Model reference

This covers Django version 0.95 and the development version. Old docs: 0.90, 0.91

A model is the single, definitive source of data about your data. It contains the essential fields and behaviors of the data you're storing. Generally, each model maps to a single database table.
模型可单独定义原数据的一些代码。它包括字段原型和你要保存的数据的方式，一般情况下，一个模型对应一个数据库表。

The basics:

• Each model is a Python class that subclasses django.db.models.Model.
• 每个模型都是django.db.models.Model的一个子类
• Each attribute of the model represents a database field.
• 模型的每个属性代表一个数据库字段
• Model metadata (non-field information) goes in an inner class named Meta.
• Metadata used for Django's admin site goes into an inner class named Admin.
• With all of this, Django gives you an automatically-generated database-access API, which is explained in the Database API reference.

A companion to this document is the official repository of model examples. (In the Django source distribution, these examples are in the tests/modeltests directory.)

Quick example

This example model defines a Person, which has a first_name and last_name:
下面的例子定义了一个Person模型，有first_name last_name两个字段：

from django.db import models

class Person(models.Model):
    first_name = models.CharField(maxlength=30)
    last_name = models.CharField(maxlength=30)

first_name and last_name are fields of the model. Each field is specified as a class attribute, and each attribute maps to a database column.

The above Person model would create a database table like this:

CREATE TABLE myapp_person (
    "id" serial NOT NULL PRIMARY KEY,
    "first_name" varchar(30) NOT NULL,
    "last_name" varchar(30) NOT NULL
);

Some technical notes:

• The name of the table, myapp_person, is automatically derived from some model metadata but can be overridden. See Table names below.
• 表名myapp_person是模型系统自动创建的，但也可以自定义修改
• An id field is added automatically, but this behavior can be overriden. See Automatic primary key fields below.
• id字段是自动添加的，也可以修改
• The CREATE TABLE SQL in this example is formatted using PostgreSQL syntax, but it's worth noting Django uses SQL tailored to the database backend specified in your settings file.
• 这里的sql语句是PostgreSQL语法，但它也可以使用于你在settings文件中设置的其他sql引擎。

Fields

The most important part of a model -- and the only required part of a model -- is the list of database fields it defines. Fields are specified by class attributes.
字段是模型中最重要的部分，也是模型的必须组成部分，它是数据库表定义的字段的一个列表，它可通过类的属性来定义。

Example:

class Musician(models.Model):
    first_name = models.CharField(maxlength=50)
    last_name = models.CharField(maxlength=50)
    instrument = models.CharField(maxlength=100)

class Album(models.Model):
    artist = models.ForeignKey(Musician)
    name = models.CharField(maxlength=100)
    release_date = models.DateField()
    num_stars = models.IntegerField()

Field name restrictions
字段名称规则

Django places only two restrictions on model field names:
Django对字段名字的使用有两条规则：

1. A field name cannot be a Python reserved word, because that would result in a Python syntax error. For example:
   字段名不能是Python的内置关键字。比如：

   class Example(models.Model):
       pass = models.IntegerField() # 'pass' is a reserved word!
   

2. A field name cannot contain more than one underscore in a row, due to the way Django's query lookup syntax works. For example:
   字段名不能连续含有两个下划线，因为Django的查询使用这种语法。比如：

   class Example(models.Model):
       foo__bar = models.IntegerField() 'foo__bar' has two underscores!
   

These limitations can be worked around, though, because your field name doesn't necessarily have to match your database column name. See db_column below.

SQL reserved words, such as join, where or select, are allowed as model field names, because Django escapes all database table names and column names in every underlying SQL query. It uses the quoting syntax of your particular database engine.

Field types

Each field in your model should be an instance of the appropriate Field class. Django uses the field class types to determine a few things:

• The database column type (e.g. INTEGER, VARCHAR).
• The widget to use in Django's admin interface, if you care to use it (e.g. <input type="text">, <select>).
• The minimal validation requirements, used in Django's admin and in manipulators.

Here are all available field types:

AutoField

An IntegerField that automatically increments according to available IDs. You usually won't need to use this directly; a primary key field will automatically be added to your model if you don't specify otherwise. See Automatic primary key fields.

BooleanField

A true/false field.

The admin represents this as a checkbox.

CharField

A string field, for small- to large-sized strings.

For large amounts of text, use TextField.

The admin represents this as an <input type="text"> (a single-line input).

CharField has an extra required argument, maxlength, the maximum length (in characters) of the field. The maxlength is enforced at the database level and in Django's validation.
CharField需要一个必须参数：maxlength，表示字段的最大长度。

CommaSeparatedIntegerField

A field of integers separated by commas. As in CharField, the maxlength argument is required.

DateField

A date field. Has a few extra optional arguments:

Argument	Description
auto_now	Automatically set the field to now every time the object is saved. Useful for "last-modified" timestamps. Note that the current date is always used; it's not just a default value that you can override.在字段每次保存时自动更新为当前时间。不能被用户覆盖更改。
auto_now_add	Automatically set the field to now when the object is first created. Useful for creation of timestamps. Note that the current date is always used; it's not just a default value that you can override.在字段首次创建时自动保存为当前时间。不能被用户覆盖更改。

The admin represents this as an <input type="text"> with a JavaScript calendar and a shortcut for "Today."

DateTimeField

A date and time field. Takes the same extra options as DateField.

The admin represents this as two <input type="text"> fields, with JavaScript shortcuts.
它将作为两个text表单域。

EmailField

A CharField that checks that the value is a valid e-mail address. This doesn't accept maxlength; its maxlength is automatically set to 75.
它没有maxlength属性，最大程度自动被设为75。

FileField

A file-upload field.

Has an extra required argument, upload_to, a local filesystem path to which files should be upload. This path may contain strftime formatting, which will be replaced by the date/time of the file upload (so that uploaded files don't fill up the given directory).

The admin represents this as an <input type="file"> (a file-upload widget).

Using a FileField or an ImageField (see below) in a model takes a few steps:

1. In your settings file, you'll need to define MEDIA_ROOT as the full path to a directory where you'd like Django to store uploaded files. (For performance, these files are not stored in the database.) Define MEDIA_URL as the base public URL of that directory. Make sure that this directory is writable by the Web server's user account.
2. Add the FileField or ImageField to your model, making sure to define the upload_to option to tell Django to which subdirectory of MEDIA_ROOT it should upload files.
3. All that will be stored in your database is a path to the file (relative to MEDIA_ROOT). You'll most likely want to use the convenience get_<fieldname>_url function provided by Django. For example, if your ImageField is called mug_shot, you can get the absolute URL to your image in a template with {{ object.get_mug_shot_url }}.

For example, say your MEDIA_ROOT is set to '/home/media', and upload_to is set to 'photos/%Y/%m/%d'. The '%Y/%m/%d' part of upload_to is strftime formatting; '%Y' is the four-digit year, '%m' is the two-digit month and '%d' is the two-digit day. If you upload a file on Jan. 15, 2007, it will be saved in the directory /home/media/photos/2007/01/15.

Note that whenever you deal with uploaded files, you should pay close attention to where you're uploading them and what type of files they are, to avoid security holes. Validate all uploaded files so that you're sure the files are what you think they are. For example, if you blindly let somebody upload files, without validation, to a directory that's within your Web server's document root, then somebody could upload a CGI or PHP script and execute that script by visiting its URL on your site. Don't allow that.

FilePathField

A field whose choices are limited to the filenames in a certain directory on the filesystem. Has three special arguments, of which the first is required:

Argument	Description
path	Required. The absolute filesystem path to a directory from which this FilePathField should get its choices. Example: "/home/images".
match	Optional. A regular expression, as a string, that FilePathField will use to filter filenames. Note that the regex will be applied to the base filename, not the full path. Example: "foo.*\.txt^", which will match a file called foo23.txt but not bar.txt or foo23.gif.
recursive	Optional. Either True or False. Default is False. Specifies whether all subdirectories of path should be included.

Of course, these arguments can be used together.

The one potential gotcha is that match applies to the base filename, not the full path. So, this example:

FilePathField(path="/home/images", match="foo.*", recursive=True)

...will match /home/images/foo.gif but not /home/images/foo/bar.gif because the match applies to the base filename (foo.gif and bar.gif).

FloatField

A floating-point number. Has two required arguments:

Argument	Description
max_digits	The maximum number of digits allowed in the number. 最长长度
decimal_places	The number of decimal places to store with the number. 小数位最长长度

For example, to store numbers up to 999 with a resolution of 2 decimal places, you'd use:

models.FloatField(..., max_digits=5, decimal_places=2)

And to store numbers up to approximately one billion with a resolution of 10 decimal places:

models.FloatField(..., max_digits=19, decimal_places=10)

The admin represents this as an <input type="text"> (a single-line input).

ImageField

Like FileField, but validates that the uploaded object is a valid image. Has two extra optional arguments, height_field and width_field, which, if set, will be auto-populated with the height and width of the image each time a model instance is saved.

Requires the Python Imaging Library.

IntegerField

An integer.

The admin represents this as an <input type="text"> (a single-line input).

IPAddressField

An IP address, in string format (i.e. "24.124.1.30").

The admin represents this as an <input type="text"> (a single-line input).

NullBooleanField

Like a BooleanField, but allows NULL as one of the options. Use this instead of a BooleanField with null=True.

The admin represents this as a <select> box with "Unknown", "Yes" and "No" choices.
在表单管理界面将显示为select 选项，有unknown、yes、no三个选项。

PhoneNumberField

A CharField that checks that the value is a valid U.S.A.-style phone number (in the format XXX-XXX-XXXX).
电话号码格式字段，格式为***-***-****

PositiveIntegerField

Like an IntegerField, but must be positive.
正整数字段

PositiveSmallIntegerField

Like a PositiveIntegerField, but only allows values under a certain (database-dependent) point.
正整数字段，但限定在数据库支持的范围之内。

SlugField

"Slug" is a newspaper term. A slug is a short label for something, containing only letters, numbers, underscores or hyphens. They're generally used in URLs.
slug时一个只含有字符、数字、下划线、连字符的字段，一般用于url。

In the Django development version, you can specify maxlength. If maxlength is not specified, Django will use a default length of 50. In previous Django versions, there's no way to override the length of 50.
默认最长程度为50

Implies db_index=True.

Accepts an extra option, prepopulate_from, which is a list of fields from which to auto-populate the slug, via JavaScript, in the object's admin form:？？？？？？

models.SlugField(prepopulate_from=("pre_name", "name"))

prepopulate_from doesn't accept DateTimeFields.

The admin represents SlugField as an <input type="text"> (a single-line input).

SmallIntegerField

Like an IntegerField, but only allows values under a certain (database-dependent) point.

TextField

A large text field.

The admin represents this as a <textarea> (a multi-line input).

TimeField

A time. Accepts the same auto-population options as DateField and DateTimeField.

The admin represents this as an <input type="text"> with some JavaScript shortcuts.

URLField

A field for a URL. If the verify_exists option is True (default), the URL given will be checked for existence (i.e., the URL actually loads and doesn't give a 404 response).
如果verify_exists被设定为true，给定的url地址会自动被检查是否存在

The admin represents this as an <input type="text"> (a single-line input).

USStateField

A two-letter U.S. state abbreviation.

The admin represents this as an <input type="text"> (a single-line input).

XMLField

A TextField that checks that the value is valid XML that matches a given schema. Takes one required argument, schema_path, which is the filesystem path to a RelaxNG schema against which to validate the field.

Field options

The following arguments are available to all field types. All are optional.

null

If True, Django will store empty values as NULL in the database. Default is False.
如果null属性被设为true，那么空值将在数据库中被保存为NULL

Note that empty string values will always get stored as empty strings, not as NULL -- so use null=True for non-string fields such as integers, booleans and dates.
需要注意的是，空字符串总是被保存为空值，而不是NULL，因此仅可对非字符串字段使用，如日期、布尔值、整数。

Avoid using null on string-based fields such as CharField and TextField unless you have an excellent reason. If a string-based field has null=True, that means it has two possible values for "no data": NULL, and the empty string. In most cases, it's redundant to have two possible values for "no data;" Django convention is to use the empty string, not NULL.
因此要避免对CharField、TextField等字符串类字段使用null属性，除非你有特殊目的。

blank

If True, the field is allowed to be blank.
如果设为true，字段允许为空。

Note that this is different than null. null is purely database-related, whereas blank is validation-related. If a field has blank=True, validation on Django's admin site will allow entry of an empty value. If a field has blank=False, the field will be required.
blank与null不同，blank对一个字段的验证环节起作用。

choices

An iterable (e.g., a list or tuple) of 2-tuples to use as choices for this field.

If this is given, Django's admin will use a select box instead of the standard text field and will limit choices to the choices given.

A choices list looks like this:

YEAR_IN_SCHOOL_CHOICES = (
    ('FR', 'Freshman'),
    ('SO', 'Sophomore'),
    ('JR', 'Junior'),
    ('SR', 'Senior'),
    ('GR', 'Graduate'),
)

The first element in each tuple is the actual value to be stored. The second element is the human-readable name for the option.

The choices list can be defined either as part of your model class:

class Foo(models.Model):
    GENDER_CHOICES = (
        ('M', 'Male'),
        ('F', 'Female'),
    )
    gender = models.CharField(maxlength=1, choices=GENDER_CHOICES)

or outside your model class altogether:

GENDER_CHOICES = (
    ('M', 'Male'),
    ('F', 'Female'),
)
class Foo(models.Model):
    gender = models.CharField(maxlength=1, choices=GENDER_CHOICES)

Finally, note that choices can be any iterable object -- not necessarily a list or tuple. This lets you construct choices dynamically. But if you find yourself hacking choices to be dynamic, you're probably better off using a proper database table with a ForeignKey. choices is meant for static data that doesn't change much, if ever.

core

For objects that are edited inline to a related object.

In the Django admin, if all "core" fields in an inline-edited object are cleared, the object will be deleted.

It is an error to have an inline-editable relation without at least one core=True field.

Please note that each field marked "core" is treated as a required field by the Django admin site. Essentially, this means you should put core=True on all required fields in your related object that is being edited inline.

db_column

The name of the database column to use for this field. If this isn't given, Django will use the field's name.
定义数据库表中的列名。

If your database column name is an SQL reserved word, or contains characters that aren't allowed in Python variable names -- notably, the hyphen -- that's OK. Django quotes column and table names behind the scenes.

db_index

If True, django-admin.py sqlindexes will output a CREATE INDEX statement for this field.
是否为本字段定义索引。

default

The default value for the field.

editable

If False, the field will not be editable in the admin or via form processing using the object's AddManipulator or ChangeManipulator classes. Default is True.

help_text

Extra "help" text to be displayed under the field on the object's admin form. It's useful for documentation even if your object doesn't have an admin form.

primary_key

If True, this field is the primary key for the model.

If you don't specify primary_key=True for any fields in your model, Django will automatically add this field:
如果你没有自己指定任何一个字段的primary_key属性为true，django会自动为你添加一个primary_key属性为true的字段id：

id = models.AutoField('ID', primary_key=True)

Thus, you don't need to set primary_key=True on any of your fields unless you want to override the default primary-key behavior.
因此，除非你有特殊需要，一般可以不必将一个字段的primary_key属性设置为true。

primary_key=True implies blank=False, null=False and unique=True. Only one primary key is allowed on an object.
如果一个字段的primary_key属性被设置为true，意味着blank=false,null=false,unique=true。一个模型中只能有自已字段primary_key属性为true。

radio_admin

By default, Django's admin uses a select-box interface (<select>) for fields that are ForeignKey or have choices set. If radio_admin is set to True, Django will use a radio-button interface instead.
默认情况下，django使用选项菜单显示那些foreignkey字段和设置有choices属性的字段，如果将radio_admin属性设置为true，将使用单选按钮显示。

Don't use this for a field unless it's a ForeignKey or has choices set.
只有在设置了foreignkey或choices集合的情况下，方可使用这个属性设置。

unique

If True, this field must be unique throughout the table.

This is enforced at the database level and at the Django admin-form level.

unique_for_date

Set this to the name of a DateField or DateTimeField to require that this field be unique for the value of the date field.

For example, if you have a field title that has unique_for_date="pub_date", then Django wouldn't allow the entry of two records with the same title and pub_date.
比如：你设置字段title的属性unique_for_date="pub_date"，意味着在不能有两个记录拥有同样的title和pub_date值。

This is enforced at the Django admin-form level but not at the database level.
这是django用于管理界面的一个限制，不是针对数据库中表记录的限制。

unique_for_month

Like unique_for_date, but requires the field to be unique with respect to the month.
同unique_for_date。

unique_for_year

Like unique_for_date and unique_for_month.
同unique_for_date和unique_for_month。

validator_list

A list of extra validators to apply to the field. Each should be a callable that takes the parameters field_data, all_data and raises django.core.validators.ValidationError for errors. (See the validator docs.)
一个字段限制情况列表。具体参见validator docs

Django comes with quite a few validators. They're in django.core.validators.
django有许多限制器，它们存放在包django.core.validators下面。

Verbose field names

Each field type, except for ForeignKey, ManyToManyField and OneToOneField, takes an optional first positional argument -- a verbose name. If the verbose name isn't given, Django will automatically create it using the field's attribute name, converting underscores to spaces.

In this example, the verbose name is "Person's first name":

first_name = models.CharField("Person's first name", maxlength=30)

In this example, the verbose name is "first name":

first_name = models.CharField(maxlength=30)

ForeignKey, ManyToManyField and OneToOneField require the first argument to be a model class, so use the verbose_name keyword argument:
由于foreignkey,manytomanyfield,onetoonefield类型的第一个属性参数必须为一个模型类名，因此必须明确使用verbose_name=" *** "的属性设置形式。

poll = models.ForeignKey(Poll, verbose_name="the related poll")
sites = models.ManyToManyField(Site, verbose_name="list of sites")
place = models.OneToOneField(Place, verbose_name="related place")

Convention is not to capitalize the first letter of the verbose_name. Django will automatically capitalize the first letter where it needs to.
习惯上verbose_name的第一个字母不用大写，django会在需要时自动将它的第一个字母大写。

Relationships

Clearly, the power of relational databases lies in relating tables to each other. Django offers ways to define the three most common types of database relationships: Many-to-one, many-to-many and one-to-one.
通常，关系数据库的强大之处就是在任何需要的表之间建立多种连接关系。django提供三种常用的连接关系：多对一、多对多、一对一。

Many-to-one relationships

To define a many-to-one relationship, use ForeignKey. You use it just like any other Field type: by including it as a class attribute of your model.
要定义一个多对一关系，可以在你的模型定义中，使用foreignkey类型字段。

ForeignKey requires a positional argument: The class to which the model is related.
foreignkey需要一个明确的指示：要关联的模型对象。

For example, if a Car model has a Manufacturer -- that is, a Manufacturer makes multiple cars but each Car only has one Manufacturer -- use the following definitions:
比如：car模型有一个属性manufacturer，一个供应商可以生产多种car，但一种car只能有一个供应商。他们之间的关系可以表示如下：

class Manufacturer(models.Model):
    # ...

class Car(models.Model):
    manufacturer = models.ForeignKey(Manufacturer)
    # ...

To create a recursive relationship -- an object that has a many-to-one relationship with itself -- use models.ForeignKey('self').

If you need to create a relationship on a model that has not yet been defined, you can use the name of the model, rather than the model object itself:

class Car(models.Model):
    manufacturer = models.ForeignKey('Manufacturer')
    # ...

class Manufacturer(models.Model):
    # ...

Note, however, that you can only use strings to refer to models in the same models.py file -- you cannot use a string to reference a model in a different application, or to reference a model that has been imported from elsewhere.
你可以使用字符串来表示还没有定义的其他model对象，但仅限于在同一个models文件内。

Behind the scenes, Django appends "_id" to the field name to create its database column name. In the above example, the database table for the Car model will have a manufacturer_id column. (You can change this explicitly by specifying db_column; see db_column below.) However, your code should never have to deal with the database column name, unless you write custom SQL. You'll always deal with the field names of your model object.

It's suggested, but not required, that the name of a ForeignKey field (manufacturer in the example above) be the name of the model, lowercase. You can, of course, call the field whatever you want. For example:

class Car(models.Model):
    company_that_makes_it = models.ForeignKey(Manufacturer)
    # ...

See the Many-to-one relationship model example for a full example.

ForeignKey fields take a number of extra arguments for defining how the relationship should work. All are optional:

Argument	Description
edit_inline	If not False, this related object is edited "inline" on the related object's page. This means that the object will not have its own admin interface. Use either models.TABULAR or models.STACKED, which, respectively, designate whether the inline-editable objects are displayed as a table or as a "stack" of fieldsets.？？？？？？
limit_choices_to	A dictionary of lookup arguments and values (see the Database API reference) that limit the available admin choices for this object. Use this with models.LazyDate to limit choices of objects by date. For example: limit_choices_to = {'pub_date__lte': models.LazyDate()} only allows the choice of related objects with a pub_date before the current date/time to be chosen.？？？？？？ Instead of a dictionary this can also be a Q object (an object with a get_sql() method) for more complex queries. Not compatible with edit_inline.
max_num_in_admin	For inline-edited objects, this is the maximum number of related objects to display in the admin. Thus, if a pizza could only have up to 10 toppings, max_num_in_admin=10 would ensure that a user never enters more than 10 toppings. Note that this doesn't ensure more than 10 related toppings ever get created. It simply controls the admin interface; it doesn't enforce things at the Python API level or database level.
min_num_in_admin	The minimum number of related objects displayed in the admin. Normally, at the creation stage, num_in_admin inline objects are shown, and at the edit stage num_extra_on_change blank objects are shown in addition to all pre-existing related objects. However, no fewer than min_num_in_admin related objects will ever be displayed.
num_extra_on_change	The number of extra blank related-object fields to show at the change stage.
num_in_admin	The default number of inline objects to display on the object page at the add stage.
raw_id_admin	Only display a field for the integer to be entered instead of a drop-down menu. This is useful when related to an object type that will have too many rows to make a select box practical. Not used with edit_inline.
related_name	The name to use for the relation from the related object back to this one. See the related objects documentation for a full explanation and example.
to_field	The field on the related object that the relation is to. By default, Django uses the primary key of the related object.

Many-to-many relationships

To define a many-to-many relationship, use ManyToManyField. You use it just like any other Field type: by including it as a class attribute of your model.

ManyToManyField requires a positional argument: The class to which the model is related.

For example, if a Pizza has multiple Topping objects -- that is, a Topping can be on multiple pizzas and each Pizza has multiple toppings -- here's how you'd represent that:

class Topping(models.Model):
    # ...

class Pizza(models.Model):
    # ...
    toppings = models.ManyToManyField(Topping)

As with ForeignKey, a relationship to self can be defined by using the string 'self' instead of the model name, and you can refer to as-yet undefined models by using a string containing the model name. However, you can only use strings to refer to models in the same models.py file -- you cannot use a string to reference a model in a different application, or to reference a model that has been imported from elsewhere.

It's suggested, but not required, that the name of a ManyToManyField (toppings in the example above) be a plural describing the set of related model objects.

Behind the scenes, Django creates an intermediary join table to represent the many-to-many relationship.

It doesn't matter which model gets the ManyToManyField, but you only need it in one of the models -- not in both.

Generally, ManyToManyField instances should go in the object that's going to be edited in the admin interface, if you're using Django's admin. In the above example, toppings is in Pizza (rather than Topping having a pizzas ManyToManyField ) because it's more natural to think about a Pizza having toppings than a topping being on multiple pizzas. The way it's set up above, the Pizza admin form would let users select the toppings.

See the Many-to-many relationship model example for a full example.

ManyToManyField objects take a number of extra arguments for defining how the relationship should work. All are optional:

Argument	Description
related_name	See the description under ForeignKey above.
filter_interface	Use a nifty unobtrusive Javascript "filter" interface instead of the usability-challenged <select multiple> in the admin form for this object. The value should be models.HORIZONTAL or models.VERTICAL (i.e. should the interface be stacked horizontally or vertically).
limit_choices_to	See the description under ForeignKey above.
symmetrical	Only used in the definition of ManyToManyFields on self. Consider the following model: class Person(models.Model): friends = models.ManyToManyField("self") When Django processes this model, it identifies that it has a ManyToManyField on itself, and as a result, it doesn't add a person_set attribute to the Person class. Instead, the ManyToManyField is assumed to be symmetrical -- that is, if I am your friend, then you are my friend. If you do not want symmetry in ManyToMany relationships with self, set symmetrical to False. This will force Django to add the descriptor for the reverse relationship, allowing ManyToMany relationships to be non-symmetrical.

One-to-one relationships

The semantics of one-to-one relationships will be changing soon, so we don't recommend you use them. If that doesn't scare you away, keep reading.

To define a one-to-one relationship, use OneToOneField. You use it just like any other Field type: by including it as a class attribute of your model.

This is most useful on the primary key of an object when that object "extends" another object in some way.

OneToOneField requires a positional argument: The class to which the model is related.

For example, if you're building a database of "places", you would build pretty standard stuff such as address, phone number, etc. in the database. Then, if you wanted to build a database of restaurants on top of the places, instead of repeating yourself and replicating those fields in the Restaurant model, you could make Restaurant have a OneToOneField to Place (because a restaurant "is-a" place).

As with ForeignKey, a relationship to self can be defined by using the string "self" instead of the model name; references to as-yet undefined models can be made by using a string containing the model name.

This OneToOneField will actually replace the primary key id field (since one-to-one relations share the same primary key), and will be displayed as a read-only field when you edit an object in the admin interface:

See the One-to-one relationship model example for a full example.

Meta options

Give your model metadata by using an inner class Meta, like so:

class Foo(models.Model):
    bar = models.CharField(maxlength=30)

    class Meta:
        # ...

Model metadata is "anything that's not a field", such as ordering options, etc.

Here's a list of all possible Meta options. No options are required. Adding class Meta to a model is completely optional.

db_table

The name of the database table to use for the model:

db_table = 'music_album'

If this isn't given, Django will use app_label + '_' + model_class_name. See "Table names" below for more.

If your database table name is an SQL reserved word, or contains characters that aren't allowed in Python variable names -- notably, the hyphen -- that's OK. Django quotes column and table names behind the scenes.

get_latest_by

The name of a DateField or DateTimeField in the model. This specifies the default field to use in your model Manager's latest() method.

Example:

get_latest_by = "order_date"

See the docs for latest() for more.

order_with_respect_to？？？

Marks this object as "orderable" with respect to the given field. This is almost always used with related objects to allow them to be ordered with respect to a parent object. For example, if an Answer relates to a Question object, and a question has more than one answer, and the order of answers matters, you'd do this:

class Answer(models.Model):
    question = models.ForeignKey(Question)
    # ...

    class Meta:
        order_with_respect_to = 'question'

ordering

The default ordering for the object, for use when obtaining lists of objects:

ordering = ['-order_date']

This is a tuple or list of strings. Each string is a field name with an optional "-" prefix, which indicates descending order. Fields without a leading "-" will be ordered ascending. Use the string "?" to order randomly.

For example, to order by a pub_date field ascending, use this:

ordering = ['pub_date']

To order by pub_date descending, use this:
降序，字符前加-

ordering = ['-pub_date']

To order by pub_date descending, then by author ascending, use this:
排序可以组合

ordering = ['-pub_date', 'author']

See Specifying ordering for more examples.

Note that, regardless of how many fields are in ordering, the admin site uses only the first field.

permissions

Extra permissions to enter into the permissions table when creating this object. Add, delete and change permissions are automatically created for each object that has admin set. This example specifies an extra permission, can_deliver_pizzas:

permissions = (("can_deliver_pizzas", "Can deliver pizzas"),)

This is a list or tuple of 2-tuples in the format (permission_code, human_readable_permission_name).

unique_together

Sets of field names that, taken together, must be unique:
某些字段的组合必须是唯一的：

unique_together = (("driver", "restaurant"),)

This is a list of lists of fields that must be unique when considered together. It's used in the Django admin and is enforced at the database level (i.e., the appropriate UNIQUE statements are included in the CREATE TABLE statement).

verbose_name

A human-readable name for the object, singular:

verbose_name = "pizza"

If this isn't given, Django will use a munged version of the class name: CamelCase becomes camel case.

verbose_name_plural

The plural name for the object:

verbose_name_plural = "stories"

If this isn't given, Django will use verbose_name + "s".

Table names

To save you time, Django automatically derives the name of the database table from the name of your model class and the app that contains it. A model's database table name is constructed by joining the model's "app label" -- the name you used in manage.py startapp -- to the model's class name, with an underscore between them.

For example, if you have an app bookstore (as created by manage.py startapp bookstore), a model defined as class Book will have a database table named bookstore_book.

To override the database table name, use the db_table parameter in class Meta.

Automatic primary key fields

By default, Django gives each model the following field:

id = models.AutoField(primary_key=True)

This is an auto-incrementing primary key.

If you'd like to specify a custom primary key, just specify primary_key=True on one of your fields. If Django sees you've explicitly set primary_key, it won't add the automatic id column.

Each model requires exactly one field to have primary_key=True.

Admin options

If you want your model to be visible to Django's admin site, give your model an inner "class Admin", like so:

class Person(models.Model):
    first_name = models.CharField(maxlength=30)
    last_name = models.CharField(maxlength=30)

    class Admin:
        # Admin options go here
        pass

The Admin class tells Django how to display the model in the admin site.

Here's a list of all possible Admin options. None of these options are required. To use an admin interface without specifying any options, use pass, like so:

class Admin:
    pass

Adding class Admin to a model is completely optional.

date_hierarchy？？？？？？

Set date_hierarchy to the name of a DateField or DateTimeField in your model, and the change list page will include a date-based drilldown navigation by that field.

Example:

date_hierarchy = 'pub_date'

fields

Set fields to control the layout of admin "add" and "change" pages.
控制django管理界面中add,change时显示的字段。

fields is a list of two-tuples, in which each two-tuple represents a <fieldset> on the admin form page. (A <fieldset> is a "section" of the form.)

The two-tuples are in the format (name, field_options), where name is a string representing the title of the fieldset and field_options is a dictionary of information about the fieldset, including a list of fields to be displayed in it.

A full example, taken from the django.contrib.flatpages.FlatPage model:

class Admin:
    fields = (
        (None, {
            'fields': ('url', 'title', 'content', 'sites')
        }),
        ('Advanced options', {
            'classes': 'collapse',
            'fields' : ('enable_comments', 'registration_required', 'template_name')
        }),
    )

This results in an admin page that looks like:

If fields isn't given, Django will default to displaying each field that isn't an AutoField and has editable=True, in a single fieldset, in the same order as the fields are defined in the model.

The field_options dictionary can have the following keys:

fields

A tuple of field names to display in this fieldset. This key is required.

Example:

{
'fields': ('first_name', 'last_name', 'address', 'city', 'state'),
}

To display multiple fields on the same line, wrap those fields in their own tuple. In this example, the first_name and last_name fields will display on the same line:

{
'fields': (('first_name', 'last_name'), 'address', 'city', 'state'),
}

classes

A string containing extra CSS classes to apply to the fieldset.

Example:

{
'classes': 'wide',
}

Apply multiple classes by separating them with spaces. Example:

{
'classes': 'wide extrapretty',
}

Two useful classes defined by the default admin-site stylesheet are collapse and wide. Fieldsets with the collapse style will be initially collapsed in the admin and replaced with a small "click to expand" link. Fieldsets with the wide style will be given extra horizontal space.

description

A string of optional extra text to be displayed at the top of each fieldset, under the heading of the fieldset. It's used verbatim, so you can use any HTML and you must escape any special HTML characters (such as ampersands) yourself.

js

A list of strings representing URLs of JavaScript files to link into the admin screen via <script src=""> tags. This can be used to tweak a given type of admin page in JavaScript or to provide "quick links" to fill in default values for certain fields.

list_display

Set list_display to control which fields are displayed on the change list page of the admin.

Example:

list_display = ('first_name', 'last_name')

If you don't set list_display, the admin site will display a single column that displays the __str__() representation of each object.

A few special cases to note about list_display:

• If the field is a ForeignKey, Django will display the __str__() of the related object.

• ManyToManyField fields aren't supported, because that would entail executing a separate SQL statement for each row in the table. If you want to do this nonetheless, give your model a custom method, and add that method's name to list_display. (See below for more on custom methods in list_display.)

• If the field is a BooleanField or NullBooleanField, Django will display a pretty "on" or "off" icon instead of True or False.

• If the string given is a method of the model, Django will call it and display the output. This method should have a short_description function attribute, for use as the header for the field.

  Here's a full example model:

  class Person(models.Model):
      name = models.CharField(maxlength=50)
      birthday = models.DateField()
  
      class Admin:
          list_display = ('name', 'decade_born_in')
  
      def decade_born_in(self):
          return self.birthday.strftime('%Y')[:3] + "0's"
      decade_born_in.short_description = 'Birth decade'
  

• If the string given is a method of the model, Django will HTML-escape the output by default. If you'd rather not escape the output of the method, give the method an allow_tags attribute whose value is True.

  Here's a full example model:

  class Person(models.Model):
      first_name = models.CharField(maxlength=50)
      last_name = models.CharField(maxlength=50)
      color_code = models.CharField(maxlength=6)
  
      class Admin:
          list_display = ('first_name', 'last_name', 'colored_name')
  
      def colored_name(self):
          return '<span style="color: #%s;">%s %s</span>' % (self.color_code, self.first_name, self.last_name)
      colored_name.allow_tags = True
  

• The __str__() method is just as valid in list_display as any other model method, so it's perfectly OK to do this:

  list_display = ('__str__', 'some_other_field')
  

• For any element of list_display that is not a field on the model, the change list page will not allow ordering by that column. This is because ordering is done at the database level, and Django has no way of knowing how to order the result of a custom method at the SQL level.

list_display_links

Set list_display_links to control which fields in list_display should be linked to the "change" page for an object.

By default, the change list page will link the first column -- the first field specified in list_display -- to the change page for each item. But list_display_links lets you change which columns are linked. Set list_display_links to a list or tuple of field names (in the same format as list_display) to link.

list_display_links can specify one or many field names. As long as the field names appear in list_display, Django doesn't care how many (or how few) fields are linked.

The only requirement is:
If you want to use list_display_links, you must define list_display.

In this example, the first_name and last_name fields will be linked on the change list page:

class Admin:
    list_display = ('first_name', 'last_name', 'birthday')
    list_display_links = ('first_name', 'last_name')

Finally, note that in order to use list_display_links, you must define list_display, too.

list_filter

Set list_filter to activate filters in the right sidebar of the change list page of the admin. This should be a list of field names, and each specified field should be either a BooleanField, DateField, DateTimeField or ForeignKey.

This example, taken from the django.contrib.auth.models.User model, shows how both list_display and list_filter work:

class Admin:
    list_display = ('username', 'email', 'first_name', 'last_name', 'is_staff')
    list_filter = ('is_staff', 'is_superuser')

The above code results in an admin change list page that looks like this:

(This example also has search_fields defined. See below.)

list_per_page

Set list_per_page to control how many items appear on each paginated admin change list page. By default, this is set to 100.

list_select_related

Set list_select_related to tell Django to use select_related() in retrieving the list of objects on the admin change list page. This can save you a bunch of database queries.

The value should be either True or False. Default is False.

Note that Django will use select_related(), regardless of this setting, if one of the list_display fields is a ForeignKey.

For more on select_related(), see the select_related() docs.

ordering

Set ordering to specify how objects on the admin change list page should be ordered. This should be a list or tuple in the same format as a model's ordering parameter.

If this isn't provided, the Django admin will use the model's default ordering.

save_as

Set save_as to enable a "save as" feature on admin change forms.

Normally, objects have three save options: "Save", "Save and continue editing" and "Save and add another". If save_as is True, "Save and add another" will be replaced by a "Save as" button.

"Save as" means the object will be saved as a new object (with a new ID), rather than the old object.
"save as"意味着记录将被保存为一个新的对象，而不是替换旧对象。

By default, save_as is set to False.

save_on_top

Set save_on_top to add save buttons across the top of your admin change forms.

Normally, the save buttons appear only at the bottom of the forms. If you set save_on_top, the buttons will appear both on the top and the bottom.
一般地，保存按钮出现在表单底部，如果设置了save_on_top，保存按钮将同时出现在表单顶部和底部。

By default, save_on_top is set to False.

search_fields

Set search_fields to enable a search box on the admin change list page. This should be set to a list of field names that will be searched whenever somebody submits a search query in that text box.

These fields should be some kind of text field, such as CharField or TextField.

When somebody does a search in the admin search box, Django splits the search query into words and returns all objects that contain each of the words, case insensitive, where each word must be in at least one of search_fields. For example, if search_fields is set to ['first_name', 'last_name'] and a user searches for john lennon, Django will do the equivalent of this SQL WHERE clause:

WHERE (first_name ILIKE '%john%' OR last_name ILIKE '%john%')
AND (first_name ILIKE '%lennon%' OR last_name ILIKE '%lennon%')

New in Django development version: For faster and/or more restrictive searches, prefix the field name with an operator:

^

Matches the beginning of the field. For example, if search_fields is set to ['^first_name', '^last_name'] and a user searches for john lennon, Django will do the equivalent of this SQL WHERE clause:

WHERE (first_name ILIKE 'john%' OR last_name ILIKE 'john%')
AND (first_name ILIKE 'lennon%' OR last_name ILIKE 'lennon%')

This query is more efficient than the normal '%john%' query, because the database only needs to check the beginning of a column's data, rather than seeking through the entire column's data. Plus, if the column has an index on it, some databases may be able to use the index for this query, even though it's a LIKE query.

=

Matches exactly, case-insensitive. For example, if search_fields is set to ['=first_name', '=last_name'] and a user searches for john lennon, Django will do the equivalent of this SQL WHERE clause:

WHERE (first_name ILIKE 'john' OR last_name ILIKE 'john')
AND (first_name ILIKE 'lennon' OR last_name ILIKE 'lennon')

Note that the query input is split by spaces, so, following this example, it's not currently not possible to search for all records in which first_name is exactly 'john winston' (containing a space).

@

Performs a full-text match. This is like the default search method but uses an index. Currently this is only available for MySQL.

Managers

A Manager is the interface through which database query operations are provided to Django models. At least one Manager exists for every model in a Django application.

The way Manager classes work is documented in the Retrieving objects section of the database API docs, but this section specifically touches on model options that customize Manager behavior.

Manager names

By default, Django adds a Manager with the name objects to every Django model class. However, if you want to use objects as a field name, or if you want to use a name other than objects for the Manager, you can rename it on a per-model basis. To rename the Manager for a given class, define a class attribute of type models.Manager() on that model. For example:

from django.db import models

class Person(models.Model):
    #...
    people = models.Manager()

Using this example model, Person.objects will generate an AttributeError exception, but Person.people.all() will provide a list of all Person objects.

Custom Managers

You can use a custom Manager in a particular model by extending the base Manager class and instantiating your custom Manager in your model.

There are two reasons you might want to customize a Manager: to add extra Manager methods, and/or to modify the initial QuerySet the Manager returns.

Adding extra Manager methods

Adding extra Manager methods is the preferred way to add "table-level" functionality to your models. (For "row-level" functionality -- i.e., functions that act on a single instance of a model object -- use Model methods, not custom Manager methods.)

A custom Manager method can return anything you want. It doesn't have to return a QuerySet.

For example, this custom Manager offers a method with_counts(), which returns a list of all OpinionPoll objects, each with an extra num_responses attribute that is the result of an aggregate query:

class PollManager(models.Manager):
    def with_counts(self):
        from django.db import connection
        cursor = connection.cursor()
        cursor.execute("""
            SELECT p.id, p.question, p.poll_date, COUNT(*)
            FROM polls_opinionpoll p, polls_response r
            WHERE p.id = r.poll_id
            GROUP BY 1, 2, 3
            ORDER BY 3 DESC""")
        result_list = []
        for row in cursor.fetchall():
            p = self.model(id=row[0], question=row[1], poll_date=row[2])
            p.num_responses = row[3]
            result_list.append(p)
        return result_list

class OpinionPoll(models.Model):
    question = models.CharField(maxlength=200)
    poll_date = models.DateField()
    objects = PollManager()

class Response(models.Model):
    poll = models.ForeignKey(Poll)
    person_name = models.CharField(maxlength=50)
    response = models.TextField()

With this example, you'd use OpinionPoll.objects.with_counts() to return that list of OpinionPoll objects with num_responses attributes.

Another thing to note about this example is that Manager methods can access self.model to get the model class to which they're attached.

Modifying initial Manager QuerySets

A Manager's base QuerySet returns all objects in the system. For example, using this model:

class Book(models.Model):
    title = models.CharField(maxlength=100)
    author = models.CharField(maxlength=50)

...the statement Book.objects.all() will return all books in the database.

You can override a Manager's base QuerySet by overriding the Manager.get_query_set() method. get_query_set() should return a QuerySet with the properties you require.

For example, the following model has two Managers -- one that returns all objects, and one that returns only the books by Roald Dahl:

# First, define the Manager subclass.
class DahlBookManager(models.Manager):
    def get_query_set(self):
        return super(DahlBookManager, self).get_query_set().filter(author='Roald Dahl')

# Then hook it into the Book model explicitly.
class Book(models.Model):
    title = models.CharField(maxlength=100)
    author = models.CharField(maxlength=50)

    objects = models.Manager() # The default manager.
    dahl_objects = DahlBookManager() # The Dahl-specific manager.

With this sample model, Book.objects.all() will return all books in the database, but Book.dahl_objects.all() will only return the ones written by Roald Dahl.

Of course, because get_query_set() returns a QuerySet object, you can use filter(), exclude() and all the other QuerySet methods on it. So these statements are all legal:

Book.dahl_objects.all()
Book.dahl_objects.filter(title='Matilda')
Book.dahl_objects.count()

This example also pointed out another interesting technique: using multiple managers on the same model. You can attach as many Manager() instances to a model as you'd like. This is an easy way to define common "filters" for your models.

For example:

class MaleManager(models.Manager):
    def get_query_set(self):
        return super(MaleManager, self).get_query_set().filter(sex='M')

class FemaleManager(models.Manager):
    def get_query_set(self):
        return super(FemaleManager, self).get_query_set().filter(sex='F')

class Person(models.Model):
    first_name = models.CharField(maxlength=50)
    last_name = models.CharField(maxlength=50)
    sex = models.CharField(maxlength=1, choices=(('M', 'Male'), ('F', 'Female')))
    people = models.Manager()
    men = MaleManager()
    women = FemaleManager()

This example allows you to request Person.men.all(), Person.women.all(), and Person.people.all(), yielding predictable results.

If you use custom Manager objects, take note that the first Manager Django encounters (in order by which they're defined in the model) has a special status. Django interprets the first Manager defined in a class as the "default" Manager. Certain operations -- such as Django's admin site -- use the default Manager to obtain lists of objects, so it's generally a good idea for the first Manager to be relatively unfiltered. In the last example, the people Manager is defined first -- so it's the default Manager.

Model methods

Define custom methods on a model to add custom "row-level" functionality to your objects. Whereas Manager methods are intended to do "table-wide" things, model methods should act on a particular model instance.

This is a valuable technique for keeping business logic in one place -- the model.

For example, this model has a few custom methods:

class Person(models.Model):
    first_name = models.CharField(maxlength=50)
    last_name = models.CharField(maxlength=50)
    birth_date = models.DateField()
    address = models.CharField(maxlength=100)
    city = models.CharField(maxlength=50)
    state = models.USStateField() # Yes, this is America-centric...

    def baby_boomer_status(self):
        "Returns the person's baby-boomer status."
        import datetime
        if datetime.date(1945, 8, 1) <= self.birth_date <= datetime.date(1964, 12, 31):
            return "Baby boomer"
        if self.birth_date < datetime.date(1945, 8, 1):
            return "Pre-boomer"
        return "Post-boomer"

    def is_midwestern(self):
        "Returns True if this person is from the Midwest."
        return self.state in ('IL', 'WI', 'MI', 'IN', 'OH', 'IA', 'MO')

    def _get_full_name(self):
        "Returns the person's full name."
        return '%s %s' % (self.first_name, self.last_name)
    full_name = property(_get_full_name)

The last method in this example is a property. Read more about properties.

A few object methods have special meaning:

__str__

__str__() is a Python "magic method" that defines what should be returned if you call str() on the object. Django uses str(obj) in a number of places, most notably as the value displayed to render an object in the Django admin site and as the value inserted into a template when it displays an object. Thus, you should always return a nice, human-readable string for the object's __str__. Although this isn't required, it's strongly encouraged.

For example:

class Person(models.Model):
    first_name = models.CharField(maxlength=50)
    last_name = models.CharField(maxlength=50)

    def __str__(self):
        return '%s %s' % (self.first_name, self.last_name)

get_absolute_url

Define a get_absolute_url() method to tell Django how to calculate the URL for an object. For example:

def get_absolute_url(self):
    return "/people/%i/" % self.id

Django uses this in its admin interface. If an object defines get_absolute_url(), the object-editing page will have a "View on site" link that will jump you directly to the object's public view, according to get_absolute_url().

Also, a couple of other bits of Django, such as the syndication-feed framework, use get_absolute_url() as a convenience to reward people who've defined the method.

It's good practice to use get_absolute_url() in templates, instead of hard-coding your objects' URLs. For example, this template code is bad:

<a href="/people/{{ object.id }}/">{{ object.name }}</a>

But this template code is good:

<a href="{{ object.get_absolute_url }}">{{ object.name }}</a>

(Yes, we know get_absolute_url() couples URLs to models, which violates the DRY principle, because URLs are defined both in a URLconf and in the model. This is a rare case in which we've intentionally violated that principle for the sake of convenience. With that said, we're working on an even cleaner way of specifying URLs in a more DRY fashion.)

Executing custom SQL

Feel free to write custom SQL statements in custom model methods and module-level methods. The object django.db.connection represents the current database connection. To use it, call connection.cursor() to get a cursor object. Then, call cursor.execute(sql, [params]) to execute the SQL and cursor.fetchone() or cursor.fetchall() to return the resulting rows. Example:

def my_custom_sql(self):
    from django.db import connection
    cursor = connection.cursor()
    cursor.execute("SELECT foo FROM bar WHERE baz = %s", [self.baz])
    row = cursor.fetchone()
    return row

connection and cursor simply use the standard Python DB-API. If you're not familiar with the Python DB-API, note that the SQL statement in cursor.execute() uses placeholders, "%s", rather than adding parameters directly within the SQL. If you use this technique, the underlying database library will automatically add quotes and escaping to your parameter(s) as necessary. (Also note that Django expects the "%s" placeholder, not the "?" placeholder, which is used by the SQLite Python bindings. This is for the sake of consistency and sanity.)

A final note: If all you want to do is a custom WHERE clause, you can just just the where, tables and params arguments to the standard lookup API. See Other lookup options.

Overriding default model methods

As explained in the database API docs, each model gets a few methods automatically -- most notably, save() and delete(). You can override these methods to alter behavior.

A classic use-case for overriding the built-in methods is if you want something to happen whenever you save an object. For example:

class Blog(models.Model):
    name = models.CharField(maxlength=100)
    tagline = models.TextField()

    def save(self):
        do_something()
        super(Blog, self).save() # Call the "real" save() method.
        do_something_else()

You can also prevent saving:

class Blog(models.Model):
    name = models.CharField(maxlength=100)
    tagline = models.TextField()

    def save(self):
        if self.name == "Yoko Ono's blog":
            return # Yoko shall never have her own blog!
        else:
            super(Blog, self).save() # Call the "real" save() method.

Models across files

It's perfectly OK to relate a model to one from another app. To do this, just import the related model at the top of the model that holds your model. Then, just refer to the other model class wherever needed. For example:

from mysite.geography.models import ZipCode

class Restaurant(models.Model):
    # ...
    zip_code = models.ForeignKey(ZipCode)

Using models

Once you have created your models, the final step is to tell Django you're going to use those models.

Do this by editing your settings file and changing the INSTALLED_APPS setting to add the name of the module that contains your models.py.

For example, if the models for your application live in the module mysite.myapp.models (the package structure that is created for an application by the manage.py startapp script), INSTALLED_APPS should read, in part:

INSTALLED_APPS = (
    #...
    'mysite.myapp',
    #...
)

Providing initial SQL data

Django provides a hook for passing the database arbitrary SQL that's executed just after the CREATE TABLE statements. Use this hook, for example, if you want to populate default records, or create SQL functions, automatically.

The hook is simple: Django just looks for a file called <appname>/sql/<modelname>.sql, where <appname> is your app directory and <modelname> is the model's name in lowercase.

In the Person example model at the top of this document, assuming it lives in an app called myapp, you could add arbitrary SQL to the file myapp/sql/person.sql. Here's an example of what the file might contain:

INSERT INTO myapp_person (first_name, last_name) VALUES ('John', 'Lennon');
INSERT INTO myapp_person (first_name, last_name) VALUES ('Paul', 'McCartney');

Each SQL file, if given, is expected to contain valid SQL. The SQL files are piped directly into the database after all of the models' table-creation statements have been executed.

The SQL files are read by the sqlinitialdata, sqlreset, sqlall and reset commands in manage.py. Refer to the manage.py documentation for more information.

Note that if you have multiple SQL data files, there's no guarantee of the order in which they're executed. The only thing you can assume is that, by the time your custom data files are executed, all the database tables already will have been created.

Database-backend-specific SQL data

There's also a hook for backend-specific SQL data. For example, you can have separate initial-data files for PostgreSQL and MySQL. For each app, Django looks for a file called <appname>/sql/<modelname>.<backend>.sql, where <appname> is your app directory, <modelname> is the model's name in lowercase and <backend> is the value of DATABASE_ENGINE in your settings file (e.g., postgresql, mysql).

Backend-specific SQL data is executed before non-backend-specific SQL data. For example, if your app contains the files sql/person.sql and sql/person.postgresql.sql and you're installing the app on PostgreSQL, Django will execute the contents of sql/person.postgresql.sql first, then sql/person.sql.

Comments

Adam Spooner July 26, 2006 at 10:52 a.m.

The unique field option does not work in FileFields or ImageFields.

In pgsql and mysql it throws a ProgrammingError.

Sebastian F July 26, 2006 at 4:35 p.m.

Seems to be missing from the documentation that by defining radio_admin=2 you can change the radio buttons to be displayed horizontally.

Sebastian F July 27, 2006 at 3:27 a.m.

Sorry, I ment vertically.

Amit Upadhyay July 28, 2006 at 6:02 a.m.

ImageField says: Like FileField, but validates that the uploaded object is a valid image. Has two extra optional arguments, height_field and width_field, which, *if set*, will be auto-populated with the height and width of the image each time a model instance is saved..

What does it have to set to? true/false? Being explicit here would avoid confusion.

Doug Napoleone July 28, 2006 at 7:45 a.m.

They are set to the names of other Integer fields on the model. (yes this needs to be explained).

Example:

__ class Example(models.Model):
____ image_height = models.PositiveIntegerField()
____ image_width = models.PositiveIntegerField()
____ image = models.ImageField(upload_to='images/', height='image_height', width='image_width')

That help?

Adam Spooner July 31, 2006 at 10:58 p.m.

Database relationship should not be coded next to each other if generic views are used. I've found that if two ForeignKeys or a ForeignKey and a ManyToMany are coded in sequence that the generic view thinks the database is empty.

Example:

from django.db import models
from django.contrib.auth.models import User
from foo.bar.models import Address

class ClubMember(models.Model):
____ name = models.CharField(maxlength=32)
____ login = models.ForeignKey(User)
____ address = models.ForeignKey(Address)

This will not work using a generic view [though it works fine with written views and template tags] but this will:

from django.db import models
from django.contrib.auth.models import User
from foo.bar.models import Address

class ClubMember(models.Model):
____ login = models.ForeignKey(User)
____ name = models.CharField(maxlength=32)
____ address = models.ForeignKey(Address)

Adam Spooner July 31, 2006 at 11:06 p.m.

The two relational fields don't play well together in 'list_display' either.

Example (using model above):

class Admin:
____ list_display = ('name', 'login', 'address')

This doesn't work, yada, yada, yada, but this does:

class Admin:
____ list_display = ('login', 'name', 'address')

Adam Spooner July 31, 2006 at 11:10 p.m.

OK, scratch the first comment on relationships, only the second is true. They can be in sequence in the model, but not in the list_display.

Who thought relationships in Django could be so picky...I thought they were only in real life. =)

Juergen August 14, 2006 at 10:35 a.m.

How does one define a DateField which is not required? I.e.

to_date = models.DateField(blank=True) gives an error

'str' object has no attribute 'strftime'

Simon Sapin August 19, 2006 at 2:51 p.m.

I needed to have an ImageField that would generate automaticaly a thumbnail and i made this : http://dev.exyr.org/django/image_with_th...
(it works with PIL)

Model example :
from django.db import models
from image_with_thumbnail.models import ImageWithThumbnailField
class Photo(models.Model):
image = ImageWithThumbnailField(upload_to='photos', thumbnail_field='thumb', thumbnail_size=(200,150))
thumb = models.ImageField(upload_to='photos_thumbs', blank=True, editable=False) # this one is autogenerated
...

Chris Bugert August 30, 2006 at 10:32 a.m.

In case your a newby to PostgreSQL(because I am):

PostgreSQL Ranges for:
SmallIntegerField :: -32768 to +32767
IntegerField :: -2147483648 to +2147483647
PositiveSmallIntegerField :: 0 to +32767
PositiveIntegerField :: 0 to +2147483647

Maximillian Dornseif September 25, 2006 at 12:13 p.m.

The Documentation should mention that raw_id_admin also works for Many-to-Many relationships - which is a nice thing.

Mikearagua October 22, 2006 at 3:38 p.m.

this post

http://groups.google.com/group/django-us...

helps with ImageField issues.

Jeremy October 27, 2006 at 2:55 a.m.

If you are trying to split models accross multiple files, be sure to look at this:

http://code.djangoproject.com/wiki/CookB...

In essence, if you want to split your "myModel" model in to a file "myModelFile.py" (in your models directory), you need to:
A) add:

class Meta: app_label = 'myApp'

to myModel

B) add:

from myModelFile import myModel

to the __init__.py file in your models directory

Orestis Markou November 5, 2006 at 8:38 a.m.

OK, if someone tries to insert objects in the database, using custom primary keys under postgres, be sure to adjust the postgres sequences or your app will barf!

Look into http://www.djangoproject.com/documentati...

David Chandek-Stark November 15, 2006 at 5:14 p.m.

For clarity, please add to the description of the 'auto_now' and 'auto_now_add' arguments to DateField and DateTimeField that the arguments must be set (I assume) to a value that Python evaluates to true in a boolean context, such as

True

or

1

Thanks ...

Michael November 28, 2006 at 5:37 p.m.

The section on FileField should mention get_FIELD_filename() as well as get_FIELD_url(), I nearly reimplemented the former before discovering it by reading the django source.

John November 29, 2006 at 12:51 p.m.

If you have multiple different objects related with models.ForeignKey and you're using edit_inline to have those objects appear inline in the Admin interface, is there a way to specify the order in which they appear? For example A is the main object, with B, C, and D as related objects, and you want to see them in order "C, D, B" under A.

Joe Heck November 29, 2006 at 7:47 p.m.

If you do an update to a field with direct SQL, it's a darn good idea to invoke:

import django.db import transaction
transaction.commit_unless_managed()

afterwards to make sure it's fully comitted

Bastian November 30, 2006 at 4:02 a.m.

On my system (Windows XP, Python 2.4, PostgreSQL with psycopg2) the FloatField value is represented as a decimal.Decimal() Python object, and not as a float().
There should be a note about that, since comparisons between float and decimal are not really meaningful in Python.

Mistyping? November 30, 2006 at 8:42 a.m.

I think it needs to be fixed "can just just the"

Ross Burton December 4, 2006 at 1:05 p.m.

Small point: you don't say if the blank option defaults to True or False.

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