Django的model查詢操作 與 查詢性能優化
1 如何 在做ORM查詢時 查看SQl的執行情況
(1) 最底層的 django.db.connection
在 django shell 中使用 python manage.py shell
>>> from django.db import connection
>>> Books.objects.all()
>>> connection.queries ## 可以查看查詢時間
[{'sql': 'SELECT "testsql_books"."id", "testsql_books"."name", "testsql_books"."author_id" FROM "testsql_books" LIMI
T 21', 'time': '0.002'}]
**(2) django-extensions 插件 **
。 pip install django-extensions
。 INSTALLED_APPS = (
...
'django_extensions',
...
)
。 在 django shell 中使用 python manage.py shell_plus --print-sql （extensions 強化）
這樣每次查詢都會 有sql 輸出
>>> 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查詢操作 以及優化
基本操作
增
models.Tb1.objects.create(c1='xx', c2='oo') 增加一條數據，可以接受字典類型數據 **kwargs
obj = models.Tb1(c1='xx', c2='oo')
obj.save()
查
models.Tb1.objects.get(id=123) # 獲取單條數據，不存在則報錯（不建議）
models.Tb1.objects.all() # 獲取全部
models.Tb1.objects.filter(name='seven') # 獲取指定條件的數據
models.Tb1.objects.exclude(name='seven') # 獲取指定條件的數據
刪
models.Tb1.objects.filter(name='seven').delete() # 刪除指定條件的數據
改
models.Tb1.objects.filter(name='seven').update(gender='0') # 將指定條件的數據更新，均支持 **kwargs
obj = models.Tb1.objects.get(id=1)
obj.c1 = '111'
obj.save() # 修改單條數據
查詢簡單操作
獲取個數
models.Tb1.objects.filter(name='seven').count()
大於，小於
models.Tb1.objects.filter(id__gt=1) # 獲取id大於1的值
models.Tb1.objects.filter(id__gte=1) # 獲取id大於等於1的值
models.Tb1.objects.filter(id__lt=10) # 獲取id小於10的值
models.Tb1.objects.filter(id__lte=10) # 獲取id小於10的值
models.Tb1.objects.filter(id__lt=10, id__gt=1) # 獲取id大於1 且 小於10的值
in
models.Tb1.objects.filter(id__in=[11, 22, 33]) # 獲取id等於11、22、33的數據
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大小寫不敏感
models.Tb1.objects.exclude(name__icontains="ven")
range
models.Tb1.objects.filter(id__range=[1, 2]) # 范圍bettwen and
其他類似
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正則匹配，iregex 不區分大小寫
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)
查詢復雜操作
FK foreign key 使用的原因:
約束
節省硬盤
但是多表查詢會降低速度，大型程序反而不使用外鍵，而是用單表(約束的時候，通過代碼判斷)
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
方式一：
Q(nid__gt=10)
Q(nid=8) | Q(nid__gt=10)
Q(Q(nid=8) | Q(nid__gt=10)) & Q(caption='root')
方式二：
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)
# 條件查詢
# 條件可以是：參數，字典，Q
select_related(self, *fields)
性能相關：表之間進行join連表操作，一次性獲取關聯的數據。
model.tb.objects.all().select_related()
model.tb.objects.all().select_related('外鍵字段')
model.tb.objects.all().select_related('外鍵字段__外鍵字段')
prefetch_related(self, *lookups)
性能相關：多表連表操作時速度會慢，使用其執行多次SQL查詢 在內存中做關聯，而不會再做連表查詢
# 第一次 獲取所有用戶表
# 第二次 獲取用戶類型表where id in (用戶表中的查到的所有用戶ID)
models.UserInfo.objects.prefetch_related('外鍵字段')
annotate(self, *args, **kwargs)
# 用於實現聚合group by查詢
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)
# 構造額外的查詢條件或者映射，如：子查詢
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):
# 倒序
models.UserInfo.objects.all().order_by('-nid').reverse()
# 注：如果存在order_by，reverse則是倒序，如果多個排序則一一倒序
下面兩個 取到的是對象，並且注意 取到的對象可以 獲取其他字段（這樣會再去查找該字段降低性能
defer(self, *fields):
models.UserInfo.objects.defer('username','id')
或
models.UserInfo.objects.filter(...).defer('username','id')
# 映射中排除某列數據
only(self, *fields):
# 僅取某個表中的數據
models.UserInfo.objects.only('username','id')
或
models.UserInfo.objects.filter(...).only('username','id')
執行原生SQL
1.connection
from django.db import connection, connections
cursor = connection.cursor()
# cursor = connections['default'].cursor()
django的settings中的db配置 ' default'，指定數據庫
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)