Question

I’m trying EF out and I do a lot of filtering based on many to many relationships. For instance I have persons, locations and a personlocation table to link the two. I also have a role and personrole table.

EDIT: Tables:  Person (personid, name)  Personlocation (personid, locationid)  Location (locationid, description)  Personrole (personid, roleid)  Role (roleid, description) 

EF will give me persons, roles and location entities. EDIT: Since EF will NOT generate the personlocation and personrole entity types, they cannot be used in the query.

How do I create a query to give me all the persons of a given location with a given role?

In SQL the query would be

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' 

I’ve looked, but I can’t seem to find a simple solution.

Answer 1

In 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)); 

query result:

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) 

Using 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'))); 

query result:

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])     )) 

using 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}); 

Query Result:

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) 

You may want test wich one is faster with large data.

Good luck.

Giuliano Lemes