• Django ManyToMany


    创建模型

    from django.db import models
    
    class 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',)
    View Code

    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TypeError
    Traceback (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>]>
    View Code

    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>]>
    View Code

    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 []>
    View Code

    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>]>
    View Code

    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 []>
    View Code

    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>]>
    View Code

    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/

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  • 原文地址:https://www.cnblogs.com/crazy-zjl/p/10255158.html
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