Question

I’m having a problem getting some data since I’m just starting to use LINQToEntities, Entity Framework and Lambda Expressions.

Let me explain my case:

I have a database with 4 tables as shown here:

when I generate the model from database in Visual Studio (2010) the result is this:

I searched for some info and turns out that since the table t_user_role only has the ids from its two parent tables, it gets abstracted in the model, and you have to use the navigation properties instead.

I had some problem getting the role info for a user on a given system (as the next function does)

    public t_role GetRoleForUser(string userId, string sysId)
    {
        entities = new secfinEntities(); //context from the model

        t_role userRole = entities.t_role.Where(r => r.t_user.Any(u => u.uid == userId) & r.sys_id == sysId).First();

        return userRole;
    }

Now I have to implement a simple search function that will look users that contain the provided string and return the user’s id and name (uid, user_name) and their role’s info (role_id, role_name) on a given system (the system info i have beforehand), so basically I wanna turn this next SQL Query into Lambda Expressions (keeping in mind that in the model the table t_user_role has been abstracted)

SELECT U.uid, U.user_name, R.role_id, R.role_name
FROM t_user U
    INNER JOIN t_user_role UR ON U.uid = UR.uid
    INNER JOIN t_role R ON UR.role_id = R.role_id
WHERE R.sys_id = @p0 -- first parameter
    AND U.user_name LIKE '%' + @p1 + '%' -- second parameter

Also, I would like to store the results of that in a List of a type I have defined as follows:

public class UserRole
{
    public string UserId { get; set; }
    public string UserName { get; set; }
    public string RoleId { get; set; }
    public string RoleName { get; set; }

    public UserRole(string uid, string uname, string rid, string rname)
    {
        UserId = uid;
        UserName = uname;
        RoleId = rid;
        RoleName = rname;
    }
}

So after explaining what I have done and what I’m trying to do first question is: how can that be done?, second: can the same be accomplished through the verbose form instead of Lambda expressions? if yes, how?

Thanks a lot in advance for your time.

Answer 1

This T-SQL:

SELECT U.uid, U.user_name, R.role_id, R.role_name 
FROM t_user U 
    INNER JOIN t_user_role UR ON U.uid = UR.uid 
    INNER JOIN t_role R ON UR.role_id = R.role_id 
WHERE R.sys_id = @p0 -- first parameter 
    AND U.user_name LIKE '%' + @p1 + '%' -- second parameter 

given your model translates to this verbose syntax (including the requirement to use your new model):

var results = (from u in entities.t_user
              from r in u.t_role
              where r.sys_id == sysIdVariable && u.user_name.Contains(userNameVariable)
              select new UserRole(u.uid, u.user_name, r.role_id, r.role_name))

I know you didn’t ask for it, but a lambda version might look like:

var results = entities.t_user.Join(entities.t_role, 
                                   x => x.t_role_id, 
                                   x => x.role_id, 
                                  (u, r) => new UserRole(u.uid, 
                                                         u.user_name, 
                                                         r.role_id, 
                                                         r.role_name))