django many as operating table

First, the relationship between the table and the table

　　One to One: (OneToOneField) relationship field no matter where Zhang Jian table can be, but it is recommended to build a relatively high frequency in the query that table

　　　　　　【publish = models.ForeignKey(to='Publish')】

　　Many: (ForeignKey) built in many-to-many fields that party

　　Many to many: (ManyToManyField) many-field no matter where Zhang Jian relationship table can be, but it is recommended to build a relatively high frequency in the query that table

　　ps: how to judge in the end what is the relationship between the table and the table

　　　　Empathy: A can have a plurality of B

　　　　　　　　　B can have a plurality of A

　 Delete additions and changes: can be a number, it can be an object

　　　　add () # add

　　　　set () # modifications

　　　　remove () # iterables not received, the object can be * querySet

　　　　clear () # Empty without mass participation

　　Set delete cascading delete:

　　　　publish = models.ForeignKey(to='Publish', on_delete=models.CASCADE)

　　　　= models.ForeignKey publish (to = 'Publish', on_delete = models.SET_NULL, null = True)   # cancel cascading deletes sure to set null = True

　　　　
　　　　CASCADE: Set cascading deletes, which removed the Press, the publishers of the corresponding book will be a delete 
　　　　SET_NULL: Cancel cascading deletes

Forward and reverse concept

models:

class Book(models.Model):
    title = models.CharField(max_length=32)
    price = models.DecimalField(max_digits=8, decimal_places=2)
    publist_date = models.DateField(auto_now_add=True)
    # publish = models.ForeignKey(to='Publish', to_field='id', on_delete=models.CASCADE,)
    publish = models.ForeignKey(to='Publish', on_delete=models.SET_NULL, null=True)
    authors = models.ManyToManyField(to='Author')  # 虚拟字段

class Publish(models.Model):
    name = models.CharField(max_length=32)
    addr = models.CharField(max_length=32)
    email = models.EmailField()  # 对应就是varchar类型

class Author(models.Model):
    name = models.CharField(max_length=32)
    age = models.IntegerField()
    authordetail = models.OneToOneField(to='AuthorDetail')

class AuthorDetail(models.Model):
    phone = models.CharField(max_length=32)
    addr = models.CharField(max_length=32)

View Code

Forward queries by field, press the reverse lookup table name in lowercase ...

one
　　forward: author --- author related fields in the table ---> authordetail by field
　　Reverse: authordetail --- author related fields table ---> author lowercase table names by
　　　　 the query jason phone number of positive inquiry
　　　　 inquiry address is: name of the author of Shandong reverse lookup

many
　　positive: book --- table associated field in book --- > publish by field
　　reverse: publish --- related field book list ---> book more books by table name in lowercase _set.all () as a publishing house corresponds to

Many-
　　Forward: book --- book table in the associated field ---> author by field
　　reverse: author --- related field book list ---> book by table name in lowercase _set.all ( ) because of a corresponding plurality of books

queries Oriental Press is publishing books published many fields reverse lookup
　　publish_obj = models.Publish.objects.filter (name = 'Oriental Press') .first ()
　　Print (publish_obj.book_set) # app01.Book.None
　　Print (publish_obj.book_set.all ())

all the books-many fields of inquiry jason wrote reverse lookup
　　author_obj = models.Author.objects.filter (name = 'Jason'). First ()
　　Print (author_obj.book_set) # app01.Book.None
　　Print (author_obj.book_set.all ())

query of the telephone number is one author name field 110 of reverse lookup
　　authordetail_obj = models .AuthorDetail.objects.filter (Phone = 110) .first ()
　　Print (authordetail_obj.author.name)

django many as operating table

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