Django contenttypes组件

Django包含一个contenttypes应用程序（app），可以跟踪Django项目中安装的所有模型（Model），提供用于处理模型的高级通用接口。

生成表结构之后有一个表，包含所有其他表

该组件主要应用于像不同的帖子和不同的照片都有评论，但是想只用一张评论表去存储，评论表中应有一个字段说明属于帖子还是照片，有一个字段说明该评论属于具体哪个帖子、哪个照片。

from django.db import models
from django.contrib.contenttypes.fields import GenericForeignKey,GenericRelation,ContentType
class Post(models.Model):
    """帖子表"""
    title = models.CharField(max_length=72)
    # 查看一个对象的全部评论用comments，创建时用GenericRelation
    comments=GenericRelation('Comment')
class Picture(models.Model):
    """图片表"""
    image = models.ImageField()
    comments = GenericRelation('Comment')

class Comment(models.Model):
    """评论表"""
    content = models.TextField()
    # post = models.ForeignKey(Post, null=True, blank=True, on_delete=models.CASCADE)
    # picture = models.ForeignKey(Picture, null=True, blank=True, on_delete=models.CASCADE)
    # 外键关联ContentType（其中有所有的表）
    content_type=models.ForeignKey(ContentType,on_delete=models.DO_NOTHING)
    # 关联数据的主键，具体某一行的id（例如具体某一个帖子的id）
    object_id=models.PositiveSmallIntegerField()
    # GenericForeignKey字段创建，在数据库中不会存在该字段
    content_object=GenericForeignKey('content_type','object_id')

from django.shortcuts import render,HttpResponse
from app01 import models
from django.contrib.contenttypes.fields import ContentType
# Create your views here.
def Test(request):
    # 创建测试数据 方式一
    # content_type_pic_obj=ContentType.objects.filter(model='picture').first()
    # picture_obj=models.Picture.objects.filter(id=1).first()
    # models.Comment.objects.create(content='图片好看2',content_type=content_type_pic_obj,object_id=picture_obj.id)
    # models.Comment.objects.create(content='图片好看3',content_type=content_type_pic_obj,object_id=picture_obj.id)
    # models.Comment.objects.create(content='图片好看4',content_type=content_type_pic_obj,object_id=picture_obj.id)
    # content_type_post_obj = ContentType.objects.filter(model='post').first()
    # post_obj_1 = models.Post.objects.filter(title='散文1').first()
    # post_obj_2 = models.Post.objects.filter(title='散文2').first()
    # models.Comment.objects.create(content='散文写的好', content_type=content_type_post_obj, object_id=post_obj_1.id)
    # models.Comment.objects.create(content='散文写的好2', content_type=content_type_post_obj, object_id=post_obj_1.id)
    # models.Comment.objects.create(content='散文写的好3', content_type=content_type_post_obj, object_id=post_obj_2.id)

    # 创建测试数据方式二
    # picture_obj = models.Picture.objects.filter(image='default_avatar.jpg').first()
    # models.Comment.objects.create(content_object=picture_obj,content='图片一般般')
    # post_obj_1 = models.Post.objects.filter(title='散文1').first()
    # models.Comment.objects.create(content_object=post_obj_1, content='文章一般般')

    # 查询一个对象的所有评论
    comment_list=models.Post.objects.filter(id=1).first().comments.all()
    print(comment_list)
    return HttpResponse('...')

"""django_contenttypes编写models URL Configuration

The `urlpatterns` list routes URLs to views. For more information please see:
    https://docs.djangoproject.com/en/2.0/topics/http/urls/
Examples:
Function views
    1. Add an import:  from my_app import views
    2. Add a URL to urlpatterns:  path('', views.home, name='home')
Class-based views
    1. Add an import:  from other_app.views import Home
    2. Add a URL to urlpatterns:  path('', Home.as_view(), name='home')
Including another URLconf
    1. Import the include() function: from django.urls import include, path
    2. Add a URL to urlpatterns:  path('blog/', include('blog.urls'))
"""
from django.contrib import admin
from django.urls import path
from app01 import views
urlpatterns = [
    path('admin/', admin.site.urls),
    path('test/', views.Test),
]