ORM13 query statement, foreign key query, multi-query single-table query double underline method

Main content: https://www.cnblogs.com/maple-shaw/articles/9403501.html

Note : If you want to run the entire Django project in a file:

You need to write to the file:

Import osif __name__ = = "__main__":    os.environ.setdefault ("Django_settings_module", "orm_operate.settings")    Import Django    django.setup ()

1 orm commonly used 13 query statements: Divided into the following four kinds of

A: Get the list of objects:

obj = models. Person.objects. All() Obj1 = models. Person.objects.Filter(id=1) Obj2 = models. Person.objects.Exclude(Name= ' Alex ') # values are special, the object list is no longer an object, but a dictionary, with the built-in and value OBJ3 = models. Person.objects.all ().values ()# Value_list is also very special, the object list is not an object, but a meta-ancestor, which contains the value of each row, Obj4 = models. Person.objects.all ().values_list ()# print (OBJ4) # Sorts the objects, the-number indicates that the reverse order can be taken. Obj5 = models. Person.objects.all ().order_by(' id ') # print (OBJ5) # must be sorted on the basis of an existing sort # obj6 = models. Person.objects.all (). order_by (' id '). Reverse ()# The second method: You can also set the ordering in the Mata method in models according to what sort Obj6 = models. Person.objects.all (). Reverse () # print (OBJ6)

B: Get the object:

  # If the condition does not exist or produces more than one data will be an error, generally not recommended to use.    OBJ7 = models. Person.objectsget (id=1)    # First gets the last object, which is the corresponding elast.    Obj8 = models. Person.objects.all (). first ()    obj9 = models. Person.objects.all (). last ()    # obj10 = models. PERSON.OBJECTS.Create(name= ', age=25)    # obj10.save ()    # Print (obj10) #     distinct  to heavy

C: Return number

    OBJ11 = models. Person.objects.all (). Count ()

D: Returns a Boolean value

OBJ12 = models. Person.objects.exclude (id=1). Exists ()

2 FOREIGN Key Query

Class book (Models. Model):    id = models. Autofield (primary_key=true)    title = models. Charfield (max_length=32) Press    = models. ForeignKey (to= ' Press ', related_name= ' books 'null=true)

Forward query:

1. The difference between press_id and press.id

    # obj1 = models. Book.objects.get (id=1)    # Print (obj1.press.id)          #从book表中取到press_id, and then find the ID in the press table = press_id Object out press.id    # Print (obj1.press_id)                                        #直接从book表里面取数据, find once

2. Association fields : associated fields __ Fields (cross-table)

Find all the books published by Hunan publishing house    books = models. Book.objects.filter (press_id= (models. Press.objects.get (name= ' Hunan satellite TV Press '). ID)
    Print (books)   execution process: First remove the ID from the press table, according to ID = press_id and then from the Book table title Books = Models. Book.objects.filter (press__name= ' Hunan Satellite TV Press ')     #使用了连表查询, check once.   Print (books)

Print (models. Book.objects.values_list ("Press__name"))

　　Reverse Query :

1. Get Management Objects :

Press_obj = press.objects.get (id = 1)

Press_obj.books Gets a management object that sets Related_name= ' books '

Press_obj.books.all () List of book objects associated with the publishing house

2. To set and delete a corresponding relationship:

Obj1 = press.objects.get (id = 2)

Obj1.books.set (Book.objects.filter (id__in = [4, 5]))

Obj1.books.remove (*book.objects.filter (id__in = [4, 5])) Press field set, null = True

3. Associated fields:

Find the publisher of the book of Happy base

obj = models. Press.objects.filter (id=models. Book.objects.get (title= ' Happy Camp '). press_id)

Print (obj)

obj = models. Press.objects.filter (books__title= ' Happy Camp '), #涉及到了一个连表查询, check once

Print (obj)

　　

More than 3 pairs of queries:

    obj = models. Author.objects.get (id__in=[1])    # print (obj)    # Print (obj.name)    print (Obj.books.all ())    # Obj.books.set ([2, 3])    # sets the corresponding relationship    # obj.books.add (2,3)    obj.books.remove (*models. Book.objects.all ())  #删除对应关系

　　

　　

　　

ORM13 query statement, foreign key query, multi-query single-table query double underline method