NHibernate Many to Many mapping Invalid Column arbitrary [table]_[id] - fluent-nhibernate

Question

Ok. I have read a lot of similar situations but all of them seems to be more related to one-to-many mappings.
long story short... Here is the code.
public class Roles
{
public virtual int RoleID { get; protected set; }
public virtual Guid RoleGUID { get; protected set; }
public virtual string RoleName { get; protected set; }
public virtual string RoleDescription { get; protected set; }
public virtual IList<User> Users { get; protected set; }
}
public class RolesMap:ClassMap<Roles>
{
public RolesMap()
{
Table("Web_Roles");
Id(x => x.RoleID);
Map(x => x.RoleDescription);
Map(x => x.RoleName);
Map(x => x.RoleGUID);
HasManyToMany(x => x.Users)
.Cascade.All()
.Inverse()
.Table("Web_UserRoles");
}
}
public class User
{
public virtual int UserID { get; protected set; }
public virtual string UserName { get; protected set; }
public virtual string Password { get; protected set; }
public virtual string Email { get; protected set; }
public virtual Guid UserGUID { get; protected set; }
public virtual IList<Roles> Roles { get; protected set; }
}
public class UserMap: ClassMap<User>
{
public UserMap()
{
Table("Web_User");
Id(x => x.UserID);
Map(x => x.UserName);
Map(x => x.Password);
Map(x => x.UserGUID);
Map(x => x.Email);
HasManyToMany(x => x.Roles)
.Cascade.All()
.Table("Web_UserRoles");
}
}
public class UserRoles
{
public virtual int RoleID { get; protected set; }
public virtual int UserID { get; protected set; }
}
So, that's the domain entities and their respectives mappings. Not biggie. Of course, no mapping for UserRoles since it's only a "mapping table".
When i get my User I get the following error.
could not initialize a collection: [FamilyDerm.AUTH.Domain.User.Roles#1][SQL: SELECT roles0_.UserID as UserID1_, roles0_.Roles_id as Roles4_1_, roles1_.RoleID as RoleID1_0_, roles1_.RoleDescription as RoleDesc2_1_0_, roles1_.RoleName as RoleName1_0_, roles1_.RoleGUID as RoleGUID1_0_ FROM Web_UserRoles roles0_ left outer join Web_Roles roles1_ on roles0_.Roles_id=roles1_.RoleID WHERE roles0_.UserID=?]
It doesn't take much to realize that the mapping is converting RoleID from my "mapping entity" UserRoles to Roles_id, which I don't understand why. I am following NHibernate exact "way" but i don't seem to get it straight.
If I replace in SQL Server Roles_id by RoleID, it works like a charm. Obviously I am having either a naming convention issue or a mapping issue itself.
As I write this, i see questions popping out to my right with similar concerns but none of them offer a solution to my problem.
Thank you.

Answer 1

Because you haven't explicitly declared the field names in the Web_UserRoles table nHibernate infers them by adding an _Id to the name of the child collection so
HasManyToMany(x => x.Users)
.Cascade.All()
.Inverse()
.Table("Web_UserRoles");
will infer a field named Users_Id in the Web_UserRoles table and likewise Roles_Id from your HasManyToMany Roles mapping.
Modifying your HasManyToMany definitions to explicitly define the Parent and Child Id columns from your ProductInProduct table should sort your issue:
HasManyToMany(x => x.Users)
.Cascade.All()
.Inverse()
.Table("Web_UserRoles")
.ParentKeyColumn("UserId")
.ChildKeyColumn("RoleId");
and
HasManyToMany(x => x.Roles)
.Cascade.All()
.Table("Web_UserRoles")
.ParentKeyColumn("RoleId")
.ChildKeyColumn("UserId");