Djangoのmodelクエリ操作とクエリの性能の最適化

1どのようにORMクエリをする時SQlの実行状況を調べますか？
（1）最下階のdjango.db.co nnection
django shellで使用します。  python manage.py shell

>>> from django.db import connection
>>> Books.objects.all()
>>> connection.queries  ##         
[{'sql': 'SELECT "testsql_books"."id", "testsql_books"."name", "testsql_books"."author_id" FROM "testsql_books" LIMI
T 21', 'time': '0.002'}]

（2）django-extensionプラグイン 

pip install django-extensions

 INSTALLED_APPS = (
    ...
    'django_extensions',
    ...
    )

django shellで使用します。  python manage.py shell_プラス  --print-sql(extensions強化)
このように毎回検索すると、sql出力があります。

>>> from testsql.models import Books
>>> Books.objects.all()
  SELECT "testsql_books"."id", "testsql_books"."name", "testsql_books"."author_id" FROM "testsql_books" LIMIT 21

Execution time: 0.002000s [Database: default]

<QuerySet [<Books: Books object>, <Books: Books object>, <Books: Books object>]>

2 ORMクエリ操作及び最適化
基本操作

 

models.Tb1.objects.create(c1='xx', c2='oo')       ，           **kwargs

obj = models.Tb1(c1='xx', c2='oo')
obj.save()

  

models.Tb1.objects.get(id=123)     #       ，      （   ）
models.Tb1.objects.all()        #     
models.Tb1.objects.filter(name='seven') #          
models.Tb1.objects.exclude(name='seven') #          

  

models.Tb1.objects.filter(name='seven').delete() #          

  
models.Tb1.objects.filter(name='seven').update(gender='0') #           ，    **kwargs
obj = models.Tb1.objects.get(id=1)
obj.c1 = '111'
obj.save()                         #       

クエリーの簡単操作

    

  models.Tb1.objects.filter(name='seven').count()

  ，  

  models.Tb1.objects.filter(id__gt=1)       #   id  1  
  models.Tb1.objects.filter(id__gte=1)       #   id    1  
  models.Tb1.objects.filter(id__lt=10)       #   id  10  
  models.Tb1.objects.filter(id__lte=10)       #   id  10  
  models.Tb1.objects.filter(id__lt=10, id__gt=1)  #   id  1     10  

in

  models.Tb1.objects.filter(id__in=[11, 22, 33])  #   id  11、22、33   
  models.Tb1.objects.exclude(id__in=[11, 22, 33]) # not in

isnull
  Entry.objects.filter(pub_date__isnull=True)

contains

  models.Tb1.objects.filter(name__contains="ven")
  models.Tb1.objects.filter(name__icontains="ven") # icontains      
  models.Tb1.objects.exclude(name__icontains="ven")

range

  models.Tb1.objects.filter(id__range=[1, 2])  #   bettwen and

    

  startswith，istartswith, endswith, iendswith,

order by

  models.Tb1.objects.filter(name='seven').order_by('id')  # asc
  models.Tb1.objects.filter(name='seven').order_by('-id')  # desc

group by--annotate

  from django.db.models import Count, Min, Max, Sum
  models.Tb1.objects.filter(c1=1).values('id').annotate(c=Count('num'))
  SELECT "app01_tb1"."id", COUNT("app01_tb1"."num") AS "c" FROM "app01_tb1" WHERE "app01_tb1"."c1" = 1 GROUP BY "app01_tb1"."id"

limit 、offset

  models.Tb1.objects.all()[10:20]

regex    ，iregex       

  Entry.objects.get(title__regex=r'^(An?|The) +')
  Entry.objects.get(title__iregex=r'^(an?|the) +')

date

  Entry.objects.filter(pub_date__date=datetime.date(2005, 1, 1))
  Entry.objects.filter(pub_date__date__gt=datetime.date(2005, 1, 1))

year

  Entry.objects.filter(pub_date__year=2005)
  Entry.objects.filter(pub_date__year__gte=2005)

month

  Entry.objects.filter(pub_date__month=12)
  Entry.objects.filter(pub_date__month__gte=6)

day

  Entry.objects.filter(pub_date__day=3)
  Entry.objects.filter(pub_date__day__gte=3)

week_day

  Entry.objects.filter(pub_date__week_day=2)
  Entry.objects.filter(pub_date__week_day__gte=2)

hour

  Event.objects.filter(timestamp__hour=23)
  Event.objects.filter(time__hour=5)
  Event.objects.filter(timestamp__hour__gte=12)

minute

  Event.objects.filter(timestamp__minute=29)
  Event.objects.filter(time__minute=46)
  Event.objects.filter(timestamp__minute__gte=29)

second

  Event.objects.filter(timestamp__second=31)
  Event.objects.filter(time__second=2)
  Event.objects.filter(timestamp__second__gte=31)

クエリの複雑な操作
FK foreign keyが使用する理由：

制約

はハードディスク

を節約します。
しかし、複数テーブルのクエリは速度を下げます。大型プログラムはむしろ外キーを使わず、単表（制約の場合はコードで判断します。）
extra

  extra(self, select=None, where=None, params=None, tables=None, order_by=None, select_params=None)
    Entry.objects.extra(select={'new_id': "select col from sometable where othercol > %s"}, select_params=(1,))
    Entry.objects.extra(where=['headline=%s'], params=['Lennon'])
    Entry.objects.extra(where=["foo='a' OR bar = 'a'", "baz = 'a'"])
    Entry.objects.extra(select={'new_id': "select id from tb where id > %s"}, select_params=(1,), order_by=['-nid'])

F

  from django.db.models import F
  models.Tb1.objects.update(num=F('num')+1)

Q

     ：
  Q(nid__gt=10)
  Q(nid=8) | Q(nid__gt=10)
  Q(Q(nid=8) | Q(nid__gt=10)) & Q(caption='root')

     ：
  con = Q()
  q1 = Q()
  q1.connector = 'OR'
  q1.children.append(('id', 1))
  q1.children.append(('id', 10))
  q1.children.append(('id', 9))
  q2 = Q()
  q2.connector = 'OR'
  q2.children.append(('c1', 1))
  q2.children.append(('c1', 10))
  q2.children.append(('c1', 9))
  con.add(q1, 'AND')
  con.add(q2, 'AND')

  models.Tb1.objects.filter(con)

exclude(self、*args、*kwargs)

  #     
  #      ：  ，  ，Q

select_.related(self、*fields)

       ：     join    ，          。
   model.tb.objects.all().select_related()
   model.tb.objects.all().select_related('    ')
   model.tb.objects.all().select_related('    __    ')

prefetch_related(self、*lookup)

      ：           ，       SQL          ，         
      #            
      #            where id in (            ID)
      models.UserInfo.objects.prefetch_related('    ')

annotate（self，*args，＊kwargs）

#       group by  

  from django.db.models import Count, Avg, Max, Min, Sum

  v = models.UserInfo.objects.values('u_id').annotate(uid=Count('u_id'))
  # SELECT u_id, COUNT(ui) AS `uid` FROM UserInfo GROUP BY u_id

  v = models.UserInfo.objects.values('u_id').annotate(uid=Count('u_id')).filter(uid__gt=1)
  # SELECT u_id, COUNT(ui_id) AS `uid` FROM UserInfo GROUP BY u_id having count(u_id) > 1

  v = models.UserInfo.objects.values('u_id').annotate(uid=Count('u_id',distinct=True)).filter(uid__gt=1)
  # SELECT u_id, COUNT( DISTINCT ui_id) AS `uid` FROM UserInfo GROUP BY u_id having count(u_id) > 1

extra(self、select=None、where=None、params=None、tables=None、order_by=None，select_params=None）

 #              ， ：   

    Entry.objects.extra(select={'new_id': "select col from sometable where othercol > %s"}, select_params=(1,))
    Entry.objects.extra(where=['headline=%s'], params=['Lennon'])
    Entry.objects.extra(where=["foo='a' OR bar = 'a'", "baz = 'a'"])
    Entry.objects.extra(select={'new_id': "select id from tb where id > %s"}, select_params=(1,), order_by=['-nid'])

reverse(self):

#   
models.UserInfo.objects.all().order_by('-nid').reverse()
#  ：    order_by，reverse    ，           

次の2つは対象となり、他のフィールドを取得することができます。
defer(self、*fields)：

 models.UserInfo.objects.defer('username','id')
 
models.UserInfo.objects.filter(...).defer('username','id')
#          

only(self、*fields)：

#          
models.UserInfo.objects.only('username','id')
 
models.UserInfo.objects.filter(...).only('username','id')

実行元SQL

1.connection
from django.db import connection, connections
cursor = connection.cursor() 
# cursor = connections['default'].cursor()
django settings  db   ' default'，     
cursor.execute("""SELECT * from auth_user where id = %s""", [1])
row = cursor.fetchone()

2 .extra
Entry.objects.extra(select={'new_id': "select id from tb where id > %s"}, select_params=(1,), order_by=['-nid'])

3 . raw     
name_map = {'a':'A','b':'B'}
models.UserInfo.objects.raw('select * from xxxx',translations=name_map)

以上が本文の全部です。皆さんの勉強に役に立つように、私たちを応援してください。