关于Rails的验证错误提示

两个参考：
http://dizzy.co.uk/ruby_on_rails/cheatsheets/active-record-validation-errors
API： http://api.rubyonrails.org/classes/ActiveRecord/Errors.html
http://api.rubyonrails.org/classes/ActiveRecord/Validations/ClassMethods.html


1. Read methods
1.1. []

object.errors[:attribute]

Alias for on method.
1.2. count

Alias for size
1.3. each

each { |attr, msg| ... }

Yields each attribute attr and associated message msg per error added.

class Company < ActiveRecord::Base
  validates_presence_of :name, :address, :email
  validates_length_of :name, :in => 5..30
end

company = Company.create(:address => '123 First St.')

company.errors.each { |attr,msg| puts "#{attr} - #{msg}" } 
  # => name - is too short (minimum is 5 characters)
  # => name - can't be blank
  # => email - can't be blank

1.4. each_full

each_full {|msg| ...}

Yields each full error message msg added. So Person.errors.add("first_name", "can't be empty") will be returned through iteration as "First name can't be empty".

class Company < ActiveRecord::Base
  validates_presence_of :name, :address, :email
  validates_length_of :name, :in => 5..30
end

company = Company.create(:address => '123 First St.')

company.errors.each_full{|msg| puts msg } 
  # => Name is too short (minimum is 5 characters)
  # => Name can't be blank
  # => Email can't be blank

1.5. full_messages

Returns all the full error messages in an array.

class Company < ActiveRecord::Base
  validates_presence_of :name, :address, :email
  validates_length_of :name, :in => 5..30
end  

company = Company.create(:address => '123 First St.')

company.errors.full_messages 
  # => ["Name is too short (minimum is 5 characters)", "Name can't be blank", "Email can't be blank"]

1.6. empty?

Returns true if no errors have been added.
1.7. length

Alias for size
1.8. on

on(:attribute)

Returns nil, if no errors are associated with the specified attribute. Returns the error message if one error is associated with the specified attribute. Returns an array of error messages if more than one error is associated with the specified attribute.

class Company < ActiveRecord::Base
  validates_presence_of :name, :address, :email
  validates_length_of :name, :in => 5..30
end

company = Company.create(:address => '123 First St.')

company.errors.on(:name)      
  # => ["is too short (minimum is 5 characters)", "can't be blank"]
company.errors.on(:email)     
  # => "can't be blank"
company.errors.on(:address)   
  # => nil

This method is also aliased as the shortcut []
1.9. on_base

Returns errors that have been assigned to the base object through add_to_base according to the normal rules of on(:attribute).
1.10. invalid?

Returns true if the specified attribute has errors associated with it.

class Company < ActiveRecord::Base
  validates_presence_of :name, :address, :email
  validates_length_of :name, :in => 5..30
end

company = Company.create(:address => '123 First St.')

company.errors.invalid?(:name)      
  # => true
company.errors.invalid?(:address)   
  # => false

1.11. size

Returns the total number of errors added. Two errors added to the same attribute will be counted as such.
1.12. to_xml

Returns an XML representation of this error object.
2. Write methods
2.1. add

add(attribute, msg = @@default_error_messages[:invalid])

Adds an error message msg to the attribute, which will be returned on a call to on(attribute) for the same attribute and ensure that this error object returns false when asked if empty?. More than one error can be added to the same attribute in which case an array will be returned on a call to on(attribute). If no msg is supplied, "invalid" is assumed.
2.2. add_on_blank

add(attribute, msg = @@default_error_messages[:blank])

Will add an error message to each of the attributes in [attributes] that is blank (for example, an empty string).
2.3. add_on_empty

add(attribute, msg = @@default_error_messages[:empty])

Will add an error message to each of the attributes in attributes that is empty.

add_on_empty(:name, :surname, :age, "empty is bad!")

2.4. add_to_base

add_to_base([attributes], msg = @@default_error_messages[:empty])

Adds an error, msg, to the base object instead of any particular attribute. This is used to report errors that don’t tie to any specific attribute, but rather to the object as a whole. These error messages don’t get prepended with any field name when iterating with each_full, so they should be complete sentences.

add_to_base(:name, :surname, :age, "default error message here")

2.5. clear

Removes all the errors that have been added to the object.
3. Default error messages

These error messages are stored in a Rails class variable, @@default_error_messages and can be changed or added to as follows:

ActiveRecord::Errors.default_error_messages[:blank] = "Your custom message here"

These default error messages are used by Rails’ built in validation class methods and some of the errors object’s write methods such as add_on_blank. You may find it useful to change them if, for example, you require your error messages in a different language.

引用

Key Value
:inclusion “is not included in the list”
:exclusion “is reserved”
:invalid “is invalid”
:confirmation “doesn’t match confirmation”
:accepted “must be accepted”
:empty “can’t be empty”
:blank “can’t be blank”
:too_long “is too long (maximum is %d characters)”
:too_short “is too short (maximum is %d characters)”
:wrong_length “is the wrong length (should be %d characters)”
:taken “has already been taken
:not_a_number “is not a number
:greater_than “must be greater than %d”
:greater_than_or_equal_to “must be greater than or equal to %d”
:equal_to “must be equal to %d”
:less_than “must be less than %d”
:less_than_or_equal_to “must be less than or equal to %d”
:odd “must be odd”
:even “must be even”

4. View Helpers
4.1. error_message_on

error_message_on(object, attribute, prepend_text = "", append_text = "", css_class = "formError")

Returns a string containing the error message attached to the attribute of the object if one exists. This error message is wrapped in a <div> tag, which can be extended to include a prepend_text and/or append_text (to properly explain the error), and a css_class to style it accordingly. Object should either be the name of an instance variable or the actual object itself. As an example, let’s say you have a model @post that has an error message on the title attribute…

error_message_on "post", "title"
  # => <div class="formError">can't be empty</div>
error_message_on @post, "title"
  # => <div class="formError">can't be empty</div>
error_message_on "post", "title", "Title simply ", " (or it won't work).", "inputError"
  # => <div class="inputError">Title simply can't be empty (or it won't work).</div>

4.1.1. Options
4.2. error_messages_for

Returns a string with a <div> containing all of the error messages for the objects located as instance variables by the names given. If more than one object is specified, the errors for the objects are displayed in the order that the object names are provided.

This <div> can be tailored by the following options…
4.2.1. Options

引用

Option Type Value
:header_tag String Used for the header of the error <div> (default is h2)
:id String The class of the error <div> (default is errorExplanation)
:class String The id of the error <div> (default is errorExplanation)
object Object The object (or array of objects) for which to display errors, if you need to escape the instance variable convention
object_name String The object name to use in the header, or any text that you prefer. If object_name is not set, the name of the first object will be used
:header_message String The message in the header of the error <div>. Pass nil or an empty string to avoid the header message altogether (default message is "X errors prohibited this object from being saved")
:message String The explanation message after the header message and before the error list. Pass nil or an empty string to avoid the explanation message altogether (default message is "There were problems with the following fields:")

To specify the display for one object, you simply provide its name as a parameter. For example, for the @user model…

error_messages_for :user

To specify more than one object, you simply list them: optionally, you can add an extra object_name parameter, which will be the name used in the header message:

error_messages_for :user_common, :user, :object_name => :user

If the objects cannot be located as instance variables, you can add an extra object parameter which gives the actual object (or aarray of objects to use)…

error_messages_for :user, :object => @question.user

This is a pre-packaged presentation of the errors with embedded strings and a certain HTML structure. If what you need is significantly different from the default presentation, it makes plenty of sense to access the object.errors instance yourself and set it up.