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This article introduces the relevant knowledge of "aggregate function, grouping function and the usage of F, Q query in django". 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!

The aggregation is aggreate (* args,**kwargs), which is calculated through QuerySet. When doing evaluation operations, use the

Grouping is annotate (* args,**kwargs). There are conditions in parentheses. When you encounter something, you have to group.

First import the functions to be used from models

From django.db.models import Min,Avg,Max Sumdef aggregate (request): # find the average price of all books ret11 = Book.objects.all (). Aggregate (Avg ("price")) # print (ret11) # {'price__avg': 51.975} # the highest price of all books ret12 = Book.objects.all (). Aggregate (MaxPrice=Max (' price')) # print (ret12) # {'MaxPrice': Decimal (' 100.00')} # egon the highest price ever published Price p = Book.objects.filter (authors__name='egon'). Price (Max ('price')) print (p) # {' price__max': Decimal ('100.00')} # Group annotate () # the highest price of a book ever published by each author # parsing, grouping by author's name, will use values, which shows the name of the field, b1 = Book.objects.values ('authors__name') .annotate (Max (' price')) print (b1) # # four authors are all associated with the same book And this book is the highest price # the lowest price book published by each publishing house b2 = Book.objects.values ('publish__name') .annotate (Min (' price')) print (b2) #

F Q query

F, mainly to make queries.

Q query can be used to query a combination of conditions & yes and, | (pipe character) or, ~ not

Def FAndQ (request): # increase the price of each book by 10 yuan, # write update book set price=price+10 # F with SQL sentence, mainly to do the query # Book.objects.all (). Update (price=F ('price') + 10) # query books with a rich beginning and a price greater than 30 Comma can do with the relationship query b4 = Book.objects.filter (title__startswith= "rich", price__gt=30) # print (b4) # # Q query can do a combination of conditions of the query & is with, | (pipe character) or, ~ non # # query books are rich at the beginning Or books with a price greater than 30, b5 = Book.objects.filter (Q (title__startswith= "rich") | Q (price__gt=60)) # print (b5) # # combined query, starting with rich, with a price greater than 60, or books with id greater than 5 b6 = Book.objects.filter (Q (title__startswith= "rich") & Q (price__gt=60) | Q (id__gt=5)) # print (b6) # query conditions if Q is not added You have to put it at the back. B7 = Book.objects.filter (Q (price__gt=60) | Q (id__gt=5), title__startswith= "rich") # print (b7) # ~ negative meaning b8 = Book.objects.filter (Q (title__startswith= "rich") & Q (price__gt=60) | Q (id__gt=5)) print (b8) "aggregate function, grouping function and introduction to F and Q query in django". Thank you for your reading. If you want to know more about the industry, you can follow the website, the editor will output more high-quality practical articles for you!

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