1 如何 在做ORM查询时 查看SQl的执行情况
(1) 最底层的 django.db.connection
在 django shell 中使用 python manage.py shell
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>>> from django.db import connection>>> Books.objects.all()>>> connection.queries ## 可以查看查询时间[{'sql': 'SELECT "testsql_books"."id", "testsql_books"."name", "testsql_books"."author_id" FROM "testsql_books" LIMIT 21', 'time': '0.002'}] |
(2) django-extensions 插件
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pip install django-extensions |
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INSTALLED_APPS = ( ... 'django_extensions', ... ) |
在 django shell 中使用 python manage.py shell_plus --print-sql （extensions 强化）
这样每次查询都会 有sql 输出
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>>> Books.objects.all() SELECT "testsql_books"."id", "testsql_books"."name", "testsql_books"."author_id" FROM "testsql_books" LIMIT 21Execution time: 0.002000s [Database: default]<QuerySet [<Books: Books object>, <Books: Books object>, <Books: Books object>]> |
2 ORM查询操作 以及优化
基本操作
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增models.Tb1.objects.create(c1='xx', c2='oo') 增加一条数据，可以接受字典类型数据 **kwargsobj = models.Tb1(c1='xx', c2='oo')obj.save() 查models.Tb1.objects.get(id=123) # 获取单条数据，不存在则报错（不建议）models.Tb1.objects.all() # 获取全部models.Tb1.objects.filter(name='seven') # 获取指定条件的数据models.Tb1.objects.exclude(name='seven') # 获取指定条件的数据 删models.Tb1.objects.filter(name='seven').delete() # 删除指定条件的数据 改models.Tb1.objects.filter(name='seven').update(gender='0') # 将指定条件的数据更新，均支持 **kwargsobj = models.Tb1.objects.get(id=1)obj.c1 = '111'obj.save() # 修改单条数据 |
查询简单操作
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获取个数 models.Tb1.objects.filter(name='seven').count()大于，小于 models.Tb1.objects.filter(id__gt=1) # 获取id大于1的值 models.Tb1.objects.filter(id__gte=1) # 获取id大于等于1的值 models.Tb1.objects.filter(id__lt=10) # 获取id小于10的值 models.Tb1.objects.filter(id__lte=10) # 获取id小于10的值 models.Tb1.objects.filter(id__lt=10, id__gt=1) # 获取id大于1 且 小于10的值in models.Tb1.objects.filter(id__in=[11, 22, 33]) # 获取id等于11、22、33的数据 models.Tb1.objects.exclude(id__in=[11, 22, 33]) # not inisnull Entry.objects.filter(pub_date__isnull=True)contains models.Tb1.objects.filter(name__contains="ven") models.Tb1.objects.filter(name__icontains="ven") # icontains大小写不敏感 models.Tb1.objects.exclude(name__icontains="ven")range models.Tb1.objects.filter(id__range=[1, 2]) # 范围bettwen and其他类似 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') # descgroup 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正则匹配，iregex 不区分大小写 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) |
查询复杂操作
FK foreign key 使用的原因:
- 约束
- 节省硬盘
但是多表查询会降低速度，大型程序反而不使用外键，而是用单表(约束的时候，通过代码判断)
extra
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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
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from django.db.models import Fmodels.Tb1.objects.update(num=F('num')+1) |
Q
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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)
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# 条件查询# 条件可以是：参数，字典，Q |
select_related(self, *fields)
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性能相关：表之间进行join连表操作，一次性获取关联的数据。model.tb.objects.all().select_related()model.tb.objects.all().select_related('外键字段')model.tb.objects.all().select_related('外键字段__外键字段') |
prefetch_related(self, *lookups)
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性能相关：多表连表操作时速度会慢，使用其执行多次SQL查询 在内存中做关联，而不会再做连表查询 # 第一次 获取所有用户表 # 第二次 获取用户类型表where id in (用户表中的查到的所有用户ID) models.UserInfo.objects.prefetch_related('外键字段') |
annotate(self, *args, **kwargs)
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# 用于实现聚合group by查询 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)
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# 构造额外的查询条件或者映射，如：子查询 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):
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# 倒序models.UserInfo.objects.all().order_by('-nid').reverse()# 注：如果存在order_by，reverse则是倒序，如果多个排序则一一倒序 |
下面两个 取到的是对象，并且注意 取到的对象可以 获取其他字段（这样会再去查找该字段降低性能
defer(self, *fields):
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models.UserInfo.objects.defer('username','id')或models.UserInfo.objects.filter(...).defer('username','id')# 映射中排除某列数据 |
only(self, *fields):
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# 仅取某个表中的数据models.UserInfo.objects.only('username','id')或models.UserInfo.objects.filter(...).only('username','id') |
执行原生SQL
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1.connectionfrom django.db import connection, connectionscursor = connection.cursor() # cursor = connections['default'].cursor()django的settings中的db配置 ' default'，指定数据库cursor.execute("""SELECT * from auth_user where id = %s""", [1])row = cursor.fetchone()2 .extraEntry.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) |
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持服务器之家。
原文链接：https://www.cnblogs.com/big-handsome-guy/p/8533908.html
