创建模型
from django.db import modelsclass Publication(models.Model):
title = models.CharField(max_length=30) def __str__(self): return self.title class Meta:
ordering = ('title',)class Article(models.Model):
headline = models.CharField(max_length=100)
publications = models.ManyToManyField(Publication) def __str__(self): return self.headline class Meta:
ordering = ('headline',)
数据迁移
#生成迁移文件，记录下在models.py文件中的改动python manage.py makemigrations ##将改动的内容作用于数据库，生成相应的数据python manage.py migrate
表操作
创建数据
执行 python manage.py shell，创建Publication和Article数据
>>> p1 = Publication(title='The Python Journal')>>> p1.save()>>> p2 = Publication(title='Science News')>>> p2.save()>>> p3 = Publication(title='Science Weekly')>>> p3.save()>>> a1 = Article(headline='Django lets you build Web apps easily')>>> a1.save()>>> a1.publications.add(p1)>>> a2 = Article(headline='NASA uses Python')>>> a2.save()>>> a2.publications.add(p1, p2)#可以同时添加多个publication对象>>> a2.publications.add(p3)>>> a2.publications.add(a1)#添加错误类型会引发TypeErrorTraceback (most recent call last): ... TypeError: 'Publication' instance expected>>> #可以用 Article 对象调用 create() 创建 并 添加 publications>>> new_publication = a2.publications.create(title='Highlights for Children')>>> # Article 对象 可以访问相关联的 publications 对象>>> a1.publications.all()<QuerySet [<Publication: The Python Journal>]> >>> a2.publications.all()<QuerySet [<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>]> >>> #publications 对象 可以访问相关联的 Article 对象>>> p2.article_set.all()<QuerySet [<Article: NASA uses Python>]> >>> p1.article_set.all()<QuerySet [<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]> >>> Publication.objects.get(id=4).article_set.all()<QuerySet [<Article: NASA uses Python>]>
查询方法
>>> #跨表查询>>> Article.objects.filter(publications__id=1)<QuerySet [<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]> >>> Article.objects.filter(publications__pk=1)<QuerySet [<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]> >>> Article.objects.filter(publications=1)<QuerySet [<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]> >>> Article.objects.filter(publications=p1)<QuerySet [<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]> >>>Article.objects.filter(publications__title__startswith="Science")<QuerySet [<Article: NASA uses Python>, <Article: NASA uses Python>]> >>>Article.objects.filter(publications__title__startswith="Science").distinct() #去重<QuerySet [<Article: NASA uses Python>]> >>> Article.objects.filter(publications__in=[1,2]).distinct()<QuerySet [<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]> >>> Article.objects.filter(publications__in=[p1,p2]).distinct()<QuerySet [<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]> >>> #反向查询>>> Publication.objects.filter(id=1)<QuerySet [<Publication: The Python Journal>]> >>> Publication.objects.filter(pk=1)<QuerySet [<Publication: The Python Journal>]> >>>Publication.objects.filter(article__headline__startswith="NASA")<QuerySet [<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>]> >>> Publication.objects.filter(article__id=1)<QuerySet [<Publication: The Python Journal>]> >>> Publication.objects.filter(article__pk=1)<QuerySet [<Publication: The Python Journal>]> >>> Publication.objects.filter(article=1)<QuerySet [<Publication: The Python Journal>]> >>> Publication.objects.filter(article=a1)<QuerySet [<Publication: The Python Journal>]> >>> Publication.objects.filter(article__in=[1,2]).distinct()<QuerySet [<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>]> >>> Publication.objects.filter(article__in=[a1,a2]).distinct()<QuerySet [<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>]> >>> #排除 exclude 一样有效>>> Article.objects.exclude(publications=p2)<QuerySet [<Article: Django lets you build Web apps easily>]>
删除数据---delete()
delete() 会删除对象的引用，其他关联对象的引用都会被删除
>>> #删除Publication，Article将无法访问>>> p1.delete()>>> Publication.objects.all()<QuerySet [<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>]> >>> a1 = Article.objects.get(pk=1)>>> a1.publications.all()#此a1关联对象被删除，已经不存在了，调用get(id=1) 会报错<QuerySet []> >>> #删除Article， Publication将无法访问>>> a2.delete()>>> Article.objects.all()<QuerySet [<Article: Django lets you build Web apps easily>]> >>> p2.article_set.all()<QuerySet []>
添加数据---add()
>>> #通过M2M的“另一端”添加关联对象>>> a4 = Article(headline='NASA finds intelligent life on Earth')>>> a4.save()>>> p2.article_set.add(a4) #Publication添加关联对象>>> p2.article_set.all()<QuerySet [<Article: NASA finds intelligent life on Earth>]> >>> a4.publications.all()<QuerySet [<Publication: Science News>]> >>> #通过另一端创建并添加关键字>>> new_article = p2.article_set.create(headline='Oxygen-free diet works wonders')>>> p2.article_set.all()<QuerySet [<Article: NASA finds intelligent life on Earth>, <Article: Oxygen-free diet works wonders>]> >>> a5 = p2.article_set.all()[1]>>> a5.publications.all()<QuerySet [<Publication: Science News>]>
移除数据---remove()
remove() 只移除当前对象的关联实例
>>> #从Article移除Publication>>> a4.publications.remove(p2)#只移除a4这个实例中的p2,其他实例中的并没有移除p2>>> p2.article_set.all()<QuerySet [<Article: Oxygen-free diet works wonders>]> >>> a4.publications.all()<QuerySet []> >>> # 从Publication移除Article>>> p2.article_set.remove(a5)>>> p2.article_set.all()<QuerySet []> >>> a5.publications.all()<QuerySet []>
设置、清除关系集合---set([..., ...])、clear()
>>> #设置关系集>>> a4.publications.all()<QuerySet [<Publication: Science News>]> >>> a4.publications.set([p3])#可以在list中添加多个，相当于把a4关联的所有publications全都替换掉>>> a4.publications.all()<QuerySet [<Publication: Science Weekly>]> >>> #清除关系集>>> p2.article_set.clear()>>> p2.article_set.all()<QuerySet []> >>> #从另一端清除>>> p2.article_set.add(a4, a5)>>> p2.article_set.all()<QuerySet [<Article: NASA finds intelligent life on Earth>, <Article: Oxygen-free diet works wonders>]> >>> a4.publications.all()<QuerySet [<Publication: Science News>, <Publication: Science Weekly>]> >>> a4.publications.clear()>>> a4.publications.all()<QuerySet []> >>> p2.article_set.all()<QuerySet [<Article: Oxygen-free diet works wonders>]>
学习自用，欢迎大神评论、指正
详情见Django文档：
https://docs.djangoproject.com/en/2.1/topics/db/examples/many_to_many/
原文出处：https://www.cnblogs.com/crazy-zjl/p/10255158.html
作者：Crazy丶土豆
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