The database additions and deletions of the ORM in Django

What is ORM? ORM (Object-relational mapping) is an object-oriented approach to the process of creating tables in a database and adding additions and deletions to data.

Simply put, a table in a database is treated as a class, and each record in the database is treated as an object. Defining a class in Django is creating a table in the database. The object that instantiates a class in Django is the addition of a record to the database. Deleting an object in Django is the deletion of a record in the database. Changing the properties of an object in Django is the value of modifying a record in the database. Traversing the property values of the Query object in Django is querying the values of the records in the database.

Here are a few of the command statements in the Django Views view function.

One, increase (Create,save)

From app01.models Import *

#create方式一: Author.objects.create (name= ' Alvin ')

#create方式二: Author.objects.create (**{"name": "Alex"})

#save方式一: Author=author (name= "Alvin")
Author.save ()

#save方式二: Author=author ()
Author.name= "Alvin"
Author.save ()

Note that the increase in Create+save two combinations, create is the increase of the action, save is added action, missing one is not in.

Second, delete (delete)

>>> Book.objects.filter (id=1). Delete () (3, {'app01. Book_authors'app01. Book': 1})

 If it is a many-to-many relationship: the Remove () and Clear () methods:

#正向
Book = models. Book.objects.filter (id=1)

#删除第三张表中和女孩1关联的所有关联信息
Book.author.clear () #清空与book中id all data associated with =1
Book.author.remove (2) #可以为id
Book.author.remove (*[1,2,3,4]) #可以为列表, Front plus *

#反向
Author = models. Author.objects.filter (id=1)
Author.book_set.clear () #清空与boy中id all data associated with =1


Third, change (update and save)
#----------------The Update method to set the corresponding property directly----------------
Models. Book.objects.filter (id=3). Update (title= "PHP")
# #sql:
# #UPDATE "App01_book" SET "title" = ' PHP ' WHERE ' App01_book '. " id "= 3; args= (' PHP ', 3)


#---------------The Save method will reset all properties again, inefficient-----------
Obj=models. Book.objects.filter (id=3) [0]
Obj.title= "Python"
Obj.save ()
# select "App01_book". " ID "," App01_book "." Title "," App01_book "." Price ",
# "App01_book". " Color "," App01_book "." Page_num ",
# "App01_book". " publisher_id "from" App01_book "WHERE" App01_book "." id "= 3 LIMIT 1;
#
# UPDATE "App01_book" SET "title" = ' Python ', "price" = 3333, "color" = ' red ', "page_num" = 556,
# "publisher_id" = 1 WHERE "App01_book". " id "= 3;

The database additions and deletions of the ORM in Django