Question

我正在尝试使用EF，我会根据多对多的关系进行大量过滤。例如，我有人，地点和人员位置表来链接这两者。我也有角色和人员表。

EDIT: Tables:

Person (personid, name)

Personlocation (personid, locationid)

Location (locationid, description)

Personrole (personid, roleid)

Role (roleid, description)

EF将给我个人，角色和位置实体。编辑：由于EF NOT 生成personlocation和personrole实体类型，因此无法在查询中使用它们。

如何创建查询以向我提供具有给定角色的给定位置的所有人员？

在SQL中，查询将是

select p.*
from persons as p
join personlocations as pl on p.personid=pl.personid
join locations       as l  on pl.locationid=l.locationid
join personroles     as pr on p.personid=pr.personid
join roles           as r  on pr.roleid=r.roleid
where r.description='Student' and l.description='Amsterdam'

我看了，但我似乎无法找到简单的解决方案。

Answer 1

注意：

由于它是在EF v1中，我们 NOT 将 PersonLocation 和 PersonRole 生成为LINQ2SQL所做的实体（上面的答案是LINQ2SQL）场景，不适用于该问题。）

解决方案1：

Persons.Include("Role").Include("Location") // Include to load Role and Location .Where(p => p.Role.Any(r => r.description == "Student") && p.Location.Any(l => l.description == "Amsterdam")).ToList();

这看起来很简单直接，但这会产生丑陋的SQL脚本而且它的表现还可以。

解决方案2：

这是故障。

// Find out all persons in the role // Return IQuerable<Person> var students = Roles.Where(r => r.description == "Student") .SelectMany(r => r.Person); // Find out all persons in the location // Return IQuerable<Person> var personsInAmsterdam = Locations.Where(l=> l.description == "Amsterdam") .SelectMany(l=>l.Person); // Find out the intersection that gives us students in Admsterdam. // Return List<Person> var AdmsterdamStudents = students.Intersect(personsInAmsterdam).ToList();

将上述三个步骤合并为一个：

//Return List<Person> var AdmsterdamStudents = Roles.Where(r => r.description == "Student") .SelectMany(r => r.Person) .Intersect ( Locations .Where(l=> l.description == "Amsterdam") .SelectMany(l=>l.Person) ).ToList();

这有点冗长。但是这会生成干净的SQL查询并且运行良好。

Answer 2

在Lambda：

    var persons = Persons.Where(p=>(p.PersonLocations.Select(ps=>ps.Location)
   .Where(l=>l.Description == "Amsterdam").Count() > 0)
    && (p.PersonRoles.Select(pr=>pr.Role)
   .Where(r=>r.Description == "Student").Count() > 0));

查询结果：

SELECT [t0].[personId] AS [PersonId], [t0].[description] AS [Description]
FROM [Persons] AS [t0]
WHERE (((
    SELECT COUNT(*)
    FROM [personlocations] AS [t1]
    INNER JOIN [Locations] AS [t2] ON [t2].[locationid] = [t1].[locationid]
    WHERE ([t2].[description] = @p0) AND ([t1].[personid] = [t0].[personId])
    )) > @p1) AND (((
    SELECT COUNT(*)
    FROM [PersonRoles] AS [t3]
    INNER JOIN [Roles] AS [t4] ON [t4].[roleid] = [t3].[roleid]
    WHERE ([t4].[description] = @p2) AND ([t3].[personid] = [t0].[personId])
    )) > @p3)

使用Contains（）：

var persons = Persons
            .Where(p=>(p.Personlocations.Select(ps=>ps.Location)
            .Select(l=>l.Description).Contains("Amsterdam")) && 
            (p.PersonRoles.Select(pr=>pr.Role)
            .Select(r=>r.Description).Contains("Student")));

查询结果：

SELECT [t0].[personId] AS [PersonId], [t0].[description] AS [Description]
FROM [Persons] AS [t0]
WHERE (EXISTS(
    SELECT NULL AS [EMPTY]
    FROM [personlocations] AS [t1]
    INNER JOIN [Locations] AS [t2] ON [t2].[locationid] = [t1].[locationid]
    WHERE ([t2].[description] = @p0) AND ([t1].[personid] = [t0].[personId])
    )) AND (EXISTS(
    SELECT NULL AS [EMPTY]
    FROM [PersonRoles] AS [t3]
    INNER JOIN [Roles] AS [t4] ON [t4].[roleid] = [t3].[roleid]
    WHERE ([t4].[description] = @p1) AND ([t3].[personid] = [t0].[personId])
    ))

使用join（）：

var persons = Persons
        .Join(Personlocations, p=>p.PersonId, ps=>ps.Personid,
(p,ps) => new {p,ps})
.Where(a => a.ps.Location.Description =="Amsterdam")
        .Join(PersonRoles,
pr=> pr.p.PersonId, r=>r.Personid,(pr,r) => new {pr.p,r})
.Where(a=>a.r.Role.Description=="Student")
        .Select(p=> new {p.p});

查询结果：

SELECT [t0].[personId] AS [PersonId], [t0].[description] AS [Description]
FROM [Persons] AS [t0]
INNER JOIN [personlocations] AS [t1] ON [t0].[personId] = [t1].[personid]
INNER JOIN [Locations] AS [t2] ON [t2].[locationid] = [t1].[locationid]
INNER JOIN [PersonRoles] AS [t3] ON [t0].[personId] = [t3].[personid]
INNER JOIN [Roles] AS [t4] ON [t4].[roleid] = [t3].[roleid]
WHERE ([t4].[description] = @p0) AND ([t2].[description] = @p1)

您可能希望测试大数据的速度更快。

祝你好运。

Giuliano Lemes

Answer 3

发现更多信息，实体处理多对多的方式和原因：

ASP.NET Blog - Many to Many Mappings in Entity Framework

Answer 4

好的，就我所知，LINQ没有任何规定。 Lambda表达式适用于任何（）。

实体框架和多对多查询无法使用？

4 个答案: