Django contenttypes組件

Django包含一個contenttypes應用程序（app），能夠跟蹤Django項目中安裝的全部模型（Model），提供用於處理模型的高級通用接口。

生成表結構以後有一個表，包含全部其餘表

該組件主要應用於像不一樣的帖子和不一樣的照片都有評論，可是想只用一張評論表去存儲，評論表中應有一個字段說明屬於帖子仍是照片，有一個字段說明該評論屬於具體哪一個帖子、哪一個照片。

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)
    # 查看一個對象的所有評論用comments，建立時用GenericRelation
    comments=GenericRelation('Comment')
class Picture(models.Model):
    """圖片表"""
    image = models.ImageField()
    comments = GenericRelation('Comment')

class Comment(models.Model):
    """評論表"""
    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)
    # 外鍵關聯ContentType（其中有全部的表）
    content_type=models.ForeignKey(ContentType,on_delete=models.DO_NOTHING)
    # 關聯數據的主鍵，具體某一行的id（例如具體某一個帖子的id）
    object_id=models.PositiveSmallIntegerField()
    # GenericForeignKey字段建立，在數據庫中不會存在該字段
    content_object=GenericForeignKey('content_type','object_id')

models.py

from django.shortcuts import render,HttpResponse
from app01 import models
from django.contrib.contenttypes.fields import ContentType
# Create your views here.
def Test(request):
    # 建立測試數據 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='圖片好看2',content_type=content_type_pic_obj,object_id=picture_obj.id)
    # models.Comment.objects.create(content='圖片好看3',content_type=content_type_pic_obj,object_id=picture_obj.id)
    # models.Comment.objects.create(content='圖片好看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='散文寫的好', content_type=content_type_post_obj, object_id=post_obj_1.id)
    # models.Comment.objects.create(content='散文寫的好2', content_type=content_type_post_obj, object_id=post_obj_1.id)
    # models.Comment.objects.create(content='散文寫的好3', content_type=content_type_post_obj, object_id=post_obj_2.id)

    # 建立測試數據方式二
    # picture_obj = models.Picture.objects.filter(image='default_avatar.jpg').first()
    # models.Comment.objects.create(content_object=picture_obj,content='圖片通常般')
    # post_obj_1 = models.Post.objects.filter(title='散文1').first()
    # models.Comment.objects.create(content_object=post_obj_1, content='文章通常般')

    # 查詢一個對象的全部評論
    comment_list=models.Post.objects.filter(id=1).first().comments.all()
    print(comment_list)
    return HttpResponse('...')

views.py

"""django_contenttypes編寫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),
]

urls.py