Dapper Many-to-Many Query

Question

I am trying to write a query to get a user in the system with all of his/her roles. There is a many-to-many relationship between users and roles. The joiner table is SystemUserUserRole with columns UserId and RoleId. My models are below:

SystemUser Model

[Key]
public int UserId { get; set; }

[Required]
[MaxLength(75)]
public string FirstName { get; set; }

[Required]
[MaxLength(75)]
public string LastName { get; set; }

[Required]
[MaxLength(15)]
public string Phone { get; set; }

[Required]
[MaxLength(250)]
public string Email { get; set; }

public virtual List<UserRole> UserRoles { get; set; }

UserRole Model

[Key]
public int RoleId { get; set; }

[Required]
[MaxLength(250)]
public string RoleName { get; set; }

public virtual List<SystemUser> SystemUsers { get; set; }

I am trying to do something below with no luck. Any suggestions on what I am doing wrong.

string query = "SELECT u.*, r.* FROM SystemUser u INNER JOIN SystemUserUserRole ur ON u.UserId = ur.UserId INNER JOIN UserRole r on ur.RoleId = r.RoleId WHERE Email = @email AND IsActive = true;";

SystemUser user = con.Query<SystemUser, UserRole, SystemUser>(query, (SystemUser, UserRole) => { SystemUser.UserRoles = UserRole; return SystemUser; }).First();

Answer 1

This will work:

In the SystemUser class, add a constructor that initialises the list:

public SystemUser()
{
    UserRoles = new List<UserRole>();
}

Then tell Dapper that for each joined row, the UserRole should be added to the SystemUser.UserRoles:

SystemUser user = con.Query<SystemUser, UserRole, SystemUser>(query,
    (SystemUser, UserRole) =>
    {
        SystemUser.UserRoles.Add(UserRole);
        return SystemUser;
    },
    splitOn: "RoleId").First();

Note that the final piece is adding the splitOn parameter, because Dapper expects identity columns to be named Id, otherwise you need to tell it the column name explicitly.