Python-day71--django Multi-table double underline query and group aggregation

#==================================== Double-underlined cross-table query ===============
# premises at this time related_name=booklist
Property Query:#Query the address of the publisher of the Linux book?     #Linux_obj=models. Book.objects.filter (title= "Linux"). First ()    #print (linux_obj.publish.name)    #    ## Query the names and prices of all the books published by The Old Boys publishing house    #    #Pubobj=models. Publish.objects.filter (name= "Old boy Publishing House"). First ()    #print (PubObj.bookList.all (). VALUES ("title", "Price")) #此时 related_name=booklistDouble underline query: . Filter (filter condition). VALUES (the value to display)

Note: If you do not define related_name, the table name is used directly when you reverse query, do not need to add _set         #Query the address of the publisher of the Linux book? --Forward Query    #Ret=models. Book.objects.filter (title= "Linux"). VALUES ("Publish__addr")    #print (ret)        #or--Reverse query    #Ret=models. Publish.objects.filter (booklist__title= "Linux"). VALUES ("addr")    #print (ret)    #Query the name and price of all books published by the Old Boys publishing house    #Ret1=models. Publish.objects.filter (name= "Old boy Publishing House"). VALUES ("Booklist__title", "Booklist__price")    #print (RET1)    #    #Ret2=models. Book.objects.filter (publish__name= "Old boy Publishing House"). VALUES ("title", "Price")    #print (Ret2)    #Query the names of all books that have been out of Egon (many-to-many)ret=models. Author.objects.filter (name="Egon"). VALUES ("Booklist__title")    Print(ret) Ret2=models. Book.objects.filter (authorlist__name="Egon"). VALUES ("title")    Print(Ret2)#the names of all books published by Egon and the names of the publishersret=models. Book.objects.filter (authorlist__name='Egon'). VALUES ('title','Publish__name')        #The name of all books published by the author of the mobile phone number starting with 151 and the name of the publisher    #Method 1:    #Ad=models. AuthorDetail.objects.filter (tel__startswith= "151"). First ()    #print (Ad.author.bookList.all (). VALUES ("title", "Publish__name"))    #Method 2Models. Book.objects.filter (authorlist__authordetail__tel__startswith="151"). VALUES ("title","Publish__name")

    #================================================================ aggregation function     fromDjango.db.modelsImportAvg,sum,count,max,min#aggregate function: aggregate
    #Check the prices of all books andret=models. Book.objects.all (). Aggregate (Pricesum=sum (" Price"))    Print(ret)#{' pricesum ': Decimal (' 166.00 ')}ret=models. Book.objects.all (). Aggregate (Priceavg=avg (" Price"), Pricesum=sum (" Price"))   #grouping function annotate function    #Query the number of authors for each bookbook_list=models. Book.objects.all (). Annotate (C=count ("Authorlist__name"))#at this time the book_list is a queryset     forBook_objinchbook_list:Print(BOOK_OBJ.C)#默认分组成一组,adds a C field to the new table after grouping    #find the cheapest books ever published by a publisherRet=models. Book.objects.all (). VALUES ('publish__id'). Annotate (Min (" Price"))#The fields within values are grouped fields    Print(ret)

Python-day71--django Multi-table double underline query and group aggregation