1.普通情况:通过log可以看出,这种情况下,访问了1次数据库
def test(request): """测试连表""" users = rbac_models.UserInfo.objects.all() for user in users: print(user.username) print(user.password) print(user.nickname) print(user.email) return HttpResponse("OK")
控制台:
2.普通情况:访问外键,可以看出,访问了4次数据库
def test(request): """测试连表""" users = rbac_models.UserInfo.objects.all() for user in users: print(user.username) print(user.usertype.name) return HttpResponse("OK")
3.使用selected_related,主动连表查询,可以看出,访问了1次数据库
def test(request): """测试连表""" users = rbac_models.UserInfo.objects.all().select_related("usertype") for user in users: print(user.username) print(user.usertype.name) return HttpResponse("OK")
4.连表降低性能,我们可以使用被动连表查询prefetch_related,可以看到访问了数据库2次,查询n个外键字段时,访问n+1次数据库.
def test(request): """测试连表""" users = rbac_models.UserInfo.objects.all().prefetch_related("usertype") for user in users: print(user.username) print(user.usertype.name) return HttpResponse("OK")
原文：http://www.cnblogs.com/jec1999/p/7642944.html