不要轻易使用linq代替sql

使用Entityframework+Reposity模式 写出的代码执行效率极低。

Linq代码：

 var querySql = rel_project_personservice.GetItems(r => r.Person).Where(w => w.ProjectId == projectId && w.Person.College.University.Province == provinceName);

转化的SQL语句：

SELECT "Extent1"."personid", "Extent1"."projectid", "Extent1"."isallotroom", "Extent1"."randomcode", "Extent1"."admissionticket",
"Extent1"."pushstatus", "Extent1"."createdtime", "Extent1"."examinationroomid", "Extent2"."id", "Extent2"."name", "Extent2"."idnumber",
 "Extent2"."gender", "Extent2"."mobile", "Extent2"."idcard", "Extent2"."email", "Extent2"."degree", "Extent2"."nation", "Extent2"."major",
"Extent2"."graduatedate", "Extent2"."livingcity", "Extent2"."accountlocation", "Extent2"."expectcity", "Extent2"."enterprisenature",
"Extent2"."expectindustry", "Extent2"."expectjob", "Extent2"."collegeid", "Extent2"."status", "Extent2"."signuptype",
"Extent2"."createdtime" AS "createdtime1", "Extent2"."modifiedtime", "Extent2"."createdby", "Extent2"."modifiedby",
"Extent2"."classname", "Extent2"."idcardtype", "Extent2"."birthday", "Extent2"."xzid", "Extent2"."szid", "Extent2"."testcity",
"Extent2"."graduateschool", "Extent2"."degreeid", "Extent2"."nationid", "Extent2"."majorid", "Extent2"."accountlocationid",
"Extent2"."livingcityid", "Extent2"."expectcityid", "Extent2"."enterprisenatureid", "Extent2"."expectindustryid",
"Extent2"."expectjobid", "Extent2"."testcityid" FROM "public"."rel_project_person" AS "Extent1" INNER JOIN "public"."person" AS "Extent2"
ON "Extent1"."personid" = "Extent2"."id" LEFT OUTER JOIN "public"."college" AS "Extent3" ON "Extent2"."collegeid" = "Extent3"."id"
 LEFT OUTER JOIN "public"."university" AS "Extent4" ON "Extent3"."universityid" = "Extent4"."id"
 WHERE "Extent1"."projectid" = 11 AND ("Extent4"."province" = '北京' OR "Extent4"."province" IS NULL )

linq转出来的语句在数据库上执行，花费40多秒:

Total query runtime: 40.1 secs
检索到  行。

实现同样的业务，自己写的sql语句：

Select C.UNIVERSITYID,c.name,count(p.id)
from Person p
join Rel_Project_Person R on P.id =R.PersonID
join College C on p.CollegeID = C.id
where R.ProjectId = and C.universityid IN
(
Select id from University where Province = '北京'
)
group by C.UNIVERSITYID,c.name

执行自己写的sql，花费不到1秒：

Total query runtime:  msec
检索到  行。