13.Django Database Models&orm Supplementary table operation supplement and other Knowledge Points supplement (ii)

A. Foreign key association.

If you say, now there are two tables, a user table, the table contains information about users ' accounts, and a usertype table, which holds the type of user account.

From django.db import Models

Class Usertype (models. Model):

#用户类型表, although the ID field is not created, the ID field is created automatically.

Type = models. Charfield (MAX_LENGTH=32)

Class User (models. Model):

#用户表

Username = models. Charfield (MAX_LENGTH=16)

Password = models. Charfield (max_length=100)

Utype = models. ForeignKey (' usertype ') #创建外键, associated usertype table

#python manage.py makemigrations

#python manage.py Migrate

Second, insert data.

Next, you begin inserting data into the table.

From APP01 import Models

def test (Request):

Models. UserType.objects.create (type= ' admin ')

Models. UserType.objects.create (type= ' user ')

Models. User.objects.create (username= ' admin ', password= ' admin ', utype_id=1)

Models. User.objects.create (username= ' aaa ', password= ' 123 ', utype_id=2)

Models. User.objects.create (username= ' BBB ', password= ' 123 ', utype_id=2)

return HttpResponse (' test ')

#在User用户表中, three rows of data were inserted.

#在业务中可以理解为创建了三个账户, the admin corresponds to the user admin type, the aaa,bbb corresponds to the common user type.

Third, find the data.

1. Cross-table query, forward lookup example.

result = models. User.objects.all () #queryset object Queryset[obj,obj,obj]

For obj in result:

Print (Obj.username,obj.password.obj.utype_id,obj.utype.type)

The output results are as follows:

Admin Admin 1 Admin

AAA 123 2 User

BBB 123 2 User

2. Cross-table query, reverse lookup example.

If there is a need now, find the user through usertype.

Examples are as follows:

obj = models. UserType.objects.all (). First () #取出usertype表中的第一个对象

#print (Obj.user_set.all ()) #返回一个queryset类型的数据, all users of this type will be listed.

#！！！！ Attention!! The user in this obj.user_set represents the user table, but in Django, if you need to reverse lookup!! Reverse lookup of the table must be lowercase!! and follow _set!! in the back.

Print (' User type ', obj.id,obj.type)

For row in Obj.user_set.all (): # Obj.user_set.all () takes out all the user types that correspond to the first record in the Usertype table, returns a Queryset type, The contents of the row variable at this time are the user object in Queryset.

Print (Row.username,row.password)

The output results are as follows:

Admin Admin

#也就是说, the reverse lookup method is the table name lowercase plus _set (underscore set).

Reverse lookup can also be filtered by filter:

obj = models. UserType.objects.all ()

For item in obj:

Print (Item.type,item.user_set.filter (username= ' admin '))

3. Some additional notes on Django Orm.

#！ When returning a single record, it returns an object with the same name as the table! #

#！ When returning multiple records, a Queryset object must be returned! #

About values:queryset[{' username ': ' xxx ', ' password ': ' xxx '}] returns the data as a dictionary.

result = models. User.objects,all (). VALUES (' username ', ' password ') #生成一个queryset数据类型, but this query results only username columns and password columns.

#不过不同的是, the queryset in this is not an object, but a dictionary. queryset[{' username ': ' xxx ', ' password ': ' xxx '}]

For row in result:

Print (row) #获取queryset中的字典数据类型.

About Values_list:

result = models. User.objects,all (). Values_list (' username ', ' password ')

#生成一个queryset数据类型, but this query results only username columns and password columns, except that the Ganso type is stored in Queryset.

# queryset[(' username ', ' xxx '), (' Password ', ' xxx ')]

！！ How do I cross tables when using values and values_list?

Double-underline _ _ Cross-table forward lookup:

res = models. User.object.all (). VALUES (' id ', ' username ', ' password ', ' Utype_ _type ') #utype字段通过外键关联了UserType表, Use the Utype field to cross the table to fetch the contents of the Type field in the Usertype table.

Summarize:

If you do not use the values method or the Values_list method, only the object is returned.

Use the values method to return the dictionary.

The Vlaues_list method is used to return the Ganso.

13.Django Database Models&orm Supplementary table operation supplement and other Knowledge Points supplement (ii)