Make query with one join instead of two - nhibernate

Question

I've very simple data schema of two tables with many-to-many relationship:
CREATE TABLE Users
(
UserId int,
UserName varchar
)
CREATE TABLE Roles
(
RoleId int,
RoleName varchar
)
CREATE TABLE UserRoles
(
UserId int,
RoleId int
)
The data model and fluent mapping are also straightforward:
class UserEntity
{
public virtual int Id {get; set;}
public virtual string Name {get; set;}
public virtual IList<RoleEntity> Roles {get; set;}
}
class RoleEntity
{
public virtual int Id {get; set;}
public virtual string Name {get; set;}
public virtual IList<UserEntity> Users {get; set;}
}
class UserEntityMap : ClassMap<UserEntity>
{
public UserEntityMap()
{
Table("Users");
Id(x => x.Id).Column("UserId");
Map(x => x.Name).Column("UserName");
HasManyToMany(x => x.Roles)
.Table("dbo.UserRoles").ParentKeyColumn("UserId").ChildKeyColumn("RoleId");
}
}
class RoleEntityMap : ClassMap<RoleEntity>
{
public RoleEntityMap()
{
Table("Roles");
Id(x => x.Id).Column("RoleId");
Map(x => x.Name).Column("RoleName");
HasManyToMany(x => x.Users)
.Table("dbo.UserRoles").ParentKeyColumn("RoleId").ChildKeyColumn("UserId");
}
}
I like to query for all UserId that belong to role with RoleId 15 using NH Query. I do the following:
IList<int> list = Session.QueryOver<UserEntity>()
.Inner.JoinQueryOver<RoleEntity>(u => u.Roles)
.Where(r => r.Id == 15)
.Select(u => u.Id)
.List<int>();
The NHibernate Profiler shows that resulted SQL query is:
SELECT this_.UserId as y0_
FROM dbo.Users this_
inner join dbo.UserRoles userroles3_
on this_.UserId = userroles3_.UserId
inner join dbo.Roles user1_
on userroles3_.RoleId = user1_.RoleId
WHERE user1_.RoleId = 15 /* #p0 */
Please, advise how I can change the mapping or the query to have resulted SQL to have a single join, like this:
SELECT this_.UserId as y0_
FROM dbo.Users this_
inner join dbo.UserRoles userroles3_
on this_.UserId = userroles3_.UserId
WHERE userroles3_.RoleId = 15 /* #p0 */

Answer 1

I've found this post on StackOverflow that contains possible solution. The solution is to add an entity for UserRoles table and simply query over it like
IList<int> list = Session.QueryOver<UserRolesEntity>()
.Where(ur => ur.RoleId == 15)
.Select(ur => ur.UserId)
.List<int>();