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This article introduces the knowledge of "some common query operations in the Python model". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Catalogue

Some query operations in the model:

1. Aggregate query: aggregate () is a termination clause of QuerySet

2.Q query: if you need to execute more complex queries (such as OR statements)

3.F query: (query is a whole column of data! )

4. Grouping query

4.1 one-to-many relationship

4.2 many-to-many relationship

Some query operations in the model: 1. Aggregate query: aggregate () is a termination clause of QuerySet

It returns a dictionary containing some key-value pairs

From movie.models import Userfrom django.db.models import Count, Avg, Max, Min, Sumdef test_info (request): # aggregate query # to find the average age in User the default data format returned is a dictionary, where the key name is age__avg, and the value is the average of the specified field. Rs = User.objects.all (). Aggregate (Avg ("age")) # specifies a name by specifying the key name of the dictionary as follows. Rs = User.objects.all (). Aggregate (age=Avg ("age")) # average, maximum, minimum, summation rs = User.objects.all (). Aggregate (Avg ("age"), Max ("age"), Min ("age"), Sum ("age"))

By default (average age in User):

Specify the key name (average age in User):

2.Q query: if you need to execute more complex queries (such as OR statements)

You can use the Q object. Q objects can use the & (and) and | (or) operators; use the ~ (not) operator to denote the inverse in front of the Q object

# query rs = User.objects.filter (Q (name=' Xiaoming') | Q (name=' Xiao Hong')) in the User table where name is Xiaoming or Xiaoxong (Q) # query Student table, rs = User.objects.filter (Q (name=' Xiaoming') & Q (age=18)) 3.F query: (query a whole column of data! )

Comparison of values for two fields

# the id of the college is less than the student's student number rs = Student.objects.filter (department_id__gt=F ('s_id)) # add 1-year-old rs = User.objects.all (). Update (age=F (' age') + 1) 4 to everyone in the User table. Grouping query

Generate a separate statistical value for each object in the called QuerySet

4.1 one-to-many relationship import Student,Coursefrom django.db.models import Count# takes out the fields that need to be grouped in the student table rs = Student.objects.values () # showing all the information of all the queried data in the form of a dictionary "" output example:

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