1、一對一查詢

    models.OneToOneField(Entry)
    兩個實體類：Author , Wife
        1、通過 Author 找 Wife
            author = Author.objects.get(id=1)
            wife = author.wife
        2、通過 Wife 找 Author
            wife = Wife.objects.get(id=2)
            author = wife.author

2、一對多/多對一查詢

    model = models.ForeignKey(Entry)
    兩個實體類：Publisher(一) , Book(多)
    正向查詢：
        book 
 
= Book.objects.get(id=1)
        publisher = book.publisher
    反向查詢
        publisher = Publisher.objects.get(id=4)
        books = publisher.book_set.all()

3、多對多查詢

    1、什麼是多對多
        A表中的一條記錄可以與B表中的任意多條記錄匹配，同時B表中的每一條記錄也可以與A表中的任意多條記錄相匹配
    2、語法
        entry = models.ManyToManyField(Entry)
    
 
3、查詢
        class Author(models.Model):
            ... ...
            publish = models.ManyToManyField(Publish)
        
        正向查詢：在 Author 中查詢 Publish
            author = Author.objects.get(id=3)
            pub_list=author.publish.all()

            通過關聯屬性.all()
        反向查詢：在 Publisher 中查詢 Author
            pub 
 
= Publisher.objects.get(id=1)
            auList = pub.author_set.all()