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Detail model query operation and query performance optimization of Django

  • 2020-12-16 06:02:29
  • OfStack

How do I see the execution of SQl when I do AN ORM query

(1) The lowest level of django.db.connection

python ES14en. py shell is used in django shell 


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

(2) django - extensions plug-in 


pip install django-extensions

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

Use of python manage in django shell.py shell_plus -- ES34en-ES35en (extensions enhanced)

So each query will have sql output 


>>> 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>]>

ORM query operation and optimization

Basic operation 


 increase 

models.Tb1.objects.create(c1='xx', c2='oo')  increase 1 Can accept dictionary type data  **kwargs

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

  check 

models.Tb1.objects.get(id=123)     #  Get a single piece of data, report an error if it does not exist (not recommended) 
models.Tb1.objects.all()        #  Access to all 
models.Tb1.objects.filter(name='seven') #  Gets the data for the specified condition 
models.Tb1.objects.exclude(name='seven') #  Gets the data for the specified condition 

  delete 

models.Tb1.objects.filter(name='seven').delete() #  Deletes the data for the specified condition 

  change 
models.Tb1.objects.filter(name='seven').update(gender='0') #  Will specify the condition of the data update, both supported  **kwargs
obj = models.Tb1.objects.get(id=1)
obj.c1 = '111'
obj.save()                         #  Modify a single piece of data

Query simple operation 


 Get the number 

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

 Greater than, less than 

  models.Tb1.objects.filter(id__gt=1)       #  To obtain id Is greater than 1 The value of the 
  models.Tb1.objects.filter(id__gte=1)       #  To obtain id Greater than or equal to 1 The value of the 
  models.Tb1.objects.filter(id__lt=10)       #  To obtain id Less than 10 The value of the 
  models.Tb1.objects.filter(id__lte=10)       #  To obtain id Less than 10 The value of the 
  models.Tb1.objects.filter(id__lt=10, id__gt=1)  #  To obtain id Is greater than 1  and   Less than 10 The value of the 

in

  models.Tb1.objects.filter(id__in=[11, 22, 33])  #  To obtain id Is equal to the 11 , 22 , 33 The data of 
  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 Case insensitive 
  models.Tb1.objects.exclude(name__icontains="ven")

range

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

 Other similar 

  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 Regular matching, iregex  Case insensitive 

  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)

Query complex operation

Reasons for using FK foreign key:

The constraint Save the hard disk

But multi-table queries slow things down, and large programs don't use foreign keys, they use single tables (constrained by code)

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 


   way 1 : 
  Q(nid__gt=10)
  Q(nid=8) | Q(nid__gt=10)
  Q(Q(nid=8) | Q(nid__gt=10)) & Q(caption='root')

   way 2 : 
  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) 


  #  Conditions of the query 
  #  Conditions can be: parameters, dictionary, Q

select_related(self, *fields) 


pip install django-extensions
0

prefetch_related(self, *lookups) 


pip install django-extensions
1

annotate(self, *args, **kwargs) 


pip install django-extensions
2

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


 #  Construct additional query criteria or mappings, such as: subqueries 

    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): 


pip install django-extensions
4

The following two fetches are objects, and note that fetches can fetch other fields (which will degrade performance by looking for that field again)
defer(self, *fields): 


pip install django-extensions
5

only(self, *fields): 


pip install django-extensions
6

Execute native SQL 


pip install django-extensions
7
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