Query optimization approach

First, assume that there are three tables

 
Room
    id
    1
    2
    ..
        1000
    

User:
    id
    1
    ..
    10000


Booking:
    user_id   room_id    time_id       date
       1          1                8:00      2017-11-11
       1          2                8:00      2017-11-11
       1          3                8:00      2017-11-11
       1          4                8:00      2017-11-11
       1          5                8:00      2017-11-11

Second, demand: 2017-11-11 get all reservation information:

Print: user name, the name of the conference room, the predetermined time period

# Solution one: Perform 11 times sql statement    
BK = models.Booking.objects.filter (DATE = 2017-11-11 )
 for Item in BK:
     Print (item.time_id, item.room.caption, item.user.user ) 
    
    
# solution two: perform 1 
# the SELECT * from the User ... ... left the Join the Join Room 
BK = models.Booking.objects.filter (DATE = 2017-11-11) .select_related ( ' the User ' , ' Room ' )
 for Item in BK:
     Print (item.time_id, item.room.caption, item.user.user) 
    
# solution three: perform 3 times 
# the SELECT * 010-51287744, from the WHERE DATE = 2017-11-11 
#select * from user where id in [1,]
#select * from room where id in [1,2,3,4,5]
bk = models.Booking.objects.filter(date=2017-11-11).prefetch_related('user','room')    
for item in bk:
    print(item.time_id, item.room.caption, item.user.user)

Summary: After optimizing the SQL statements to add selsect_releated or prefetch_releated, this is only done for optimization across the table, if it is, then there is no need to single-table queries to optimize the

So when to use selsect_releated, when to use prefetch_releated it? This, as the case may be,

selsect_releated is active even table, perform a SQL

prefetch_releated not even perform three times a SQL table

Second, the second way Q query

 　　　　　　 = remove_booking Q ()
             for room_id, time_id_list in booking_info [ ' del ' ] .items ():
                 for TIME_ID in time_id_list: 
                    TEMP = Q () Q # instantiates an object is 
                    temp.connector = ' the AND '   # in a way to connect and 
                    # user_id is a field, the latter is a corresponding field value 
                    temp.children.append (( ' user_id ' , makes request.session [ ' USER_INFO ' ] [ ' ID '],))   
                    temp.children.append(('booking_date', booking_date,))
                    temp.children.append(('room_id', room_id,))
                    temp.children.append(('booking_time', time_id,))
                    remove_booking.add(temp, 'OR')   #以or的方式添加到temp