Django 框架之 自定义Filed

知识点

1. 什么时候需要自定义Field
2. 如何自定义Field
3. 举例

简介

什么时候需要自定义Field

Django 的官方Model里提供了很多的 Field，但是有时候还是不能满足我们的需求

如何自定义Field

根据需要子类化Field或者Field子类，实现序列化和反序列化

举例

1. 子类化Field
2. 子类化FileField

参考文档

代码地址：Spareibs的Github

实验步骤

自定义一个ListField的类

【fields.py】

from django.db import models
import ast

# 自定义一个ListFiled,继承与TextField这个类
class ListFiled(models.TextField):
    description = "just a listfiled"

    # 继承TextField
    def __init__(self, *args, **kwargs):
        super(ListFiled, self).__init__(*args, **kwargs)
    # 读取数据库的时候调用这个方法
    def from_db_value(self, value, expression, conn, context):
        print('from_db_value')
        if not value:
            value = []
        if isinstance(value, list):
            return value
        print('value type ', type(value))
        # 直接将字符串转换成python内置的list
        return ast.literal_eval(value)

    # 保存数据库的时候调用这个方法
    def get_prep_value(self, value):
        print("get_prep_value")
        if not value:
            return value
        print('value type ', type(value))
        return str(value)

【models.py】

from django.db import models
from .fields import ListFiled

class ListTest(models.Model):
    labels = ListFiled()

    def __str__(self):
        return "%s " % self.labels

【views.py】

rom django.shortcuts import render,HttpResponseRedirect
from .models import ListTest

# Create your views here.
def home(request):
    return render(request, 'home.html')

def testlist(req):
    # 存入数据库测试
    test = ListTest()
    test.labels = ["python", "django"]
    test.labels.append("allen")
    test.save()
    # 读取数据库测试
    obs = ListTest.objects.all()
    for ob in obs:
        print((ob.labels))

    return HttpResponseRedirect("/")

【urls.py】

from django.conf.urls import url
from . import views

urlpatterns = [
    url(r'^$', views.home, name='home'),
    url(r'^testlist/', views.testlist, name='testlist'),
]

注意：数据库同步【此步骤略】

结果显示如下

Starting development server at http://127.0.0.1:8000/
Quit the server with CTRL-BREAK.
get_prep_value
value type  
from_db_value
value type  
['python', 'django', 'allen']

文件类型的FileField

【add_file.html】

    
    



    {% csrf_token %}
    addfiles:
    {{ form.as_p }}
    

【fields.py】

from django.db.models import FileField
from django.forms import forms
from django.template.defaultfilters import filesizeformat
from django.utils.translation import ugettext_lazy as _

class ContextTypeRestrictedFileField(FileField):
    def __init__(self, content_type=None, max_upload_size=None, **kwargs):
        self.content_type = content_type
        self.max_upload_size = max_upload_size
        super(ContextTypeRestrictedFileField, self).__init__(**kwargs)

    def clean(self, *args, **kwargs):
        data = super(ContextTypeRestrictedFileField, self).clean(*args, **kwargs)
        file = data.file
        try:
            type = file.content_type
            if type != self.content_type:
                raise forms.ValidationError('pls upload right filetype')
            if file.size > self.max_upload_size:
                raise forms.ValidationError('exceed max uploadsize')
        except AttributeError:
            print("error")
            pass
        return data

【models.py】

from django.db import models
from .fields import ContextTypeRestrictedFileField

class AddPdfFileModel(models.Model):
    name = models.CharField(max_length=100)
    file = ContextTypeRestrictedFileField(content_type='application/pdf', max_upload_size=5242880, upload_to='pdf')

    def __str__(self):
        return self.name

【views.py】

from django.shortcuts import render
from .models import AddPdfFileModel
from .forms import AddPdfForm

def addfile(req):
    if req.method == 'POST':
        form = AddPdfForm(req.POST, req.FILES)
        if not form.is_valid():
            print(form.errors)
            return HttpResponseRedirect("/")
        name = form.cleaned_data['name']
        file = form.cleaned_data['file']
        add_pdf_model = AddPdfFileModel(name=name, file=file)
        add_pdf_model.save()
        print('success')
        return render(req, 'add_file.html', {'form': AddPdfForm()})
    else:
        return render(req, 'add_file.html', {'form':AddPdfForm()})

【urls.py】

from django.conf.urls import url
from . import views

urlpatterns = [
    url(r'^$', views.home, name='home'),
    url(r'^addfile/', views.addfile, name='addfile'),
]

注意：数据库同步【此步骤略】