Create a entity framework LINQ group join query to return a subset of properties from DTO and a list of another DTO, ASP.net core - asp.net

Question

So, I tried searching and couldn't really find an answer that was explicit enough and guided me to my solution so I thought I would add my problem and ultimately my solution for others to benefit.
Pardon my newness to SO (consider this my start of getting my reputation up), let me know if I do anything incorrect or forget anything.
I am trying to:
Create a controller that queries a database for all the users and their roles.
Return the list of unique users id's and email address with a List of roles.
The email address and roles are in separate tables and the pkey/fkey is the user id
The roles are returned as a list containing my AllUserInRolesDto
Every example I looked at on SO or other sites only provided examples of returning anonymous data objects back. I don't have a lot of LINQ query syntax so had me stuck for an hour or so.
Here is my DTO
namespace Lib.Dtos
{
public class AllUserInRolesDto
{
public string FullName { get; set; }
public string Email { get; set; }
public List<RoleDto> Roles { get; set; }
}
public class RoleDto
{
public string RoleName { get; set; }
}
}
I have a business layer that defines the LINQ query
public List<AllUserInRolesDto> UserAllRolesGet()
{
List<AllUserInRolesDto> getAllUsersRoles = (from u in _context.Users
join r in _context.UserInRoles on u.UserId equals r.UserId
into ur
select new Lib.Dtos.AllUserInRolesDto()
{
FullName = u.Fullname,
Email = u.Email,
Roles = ur //this was the problem line and what the docs were describing
}).ToList();
return getAllUsersRoles;
}
...and my controller
[HttpGet("GetAllUserRolesList")]
public IActionResult GetAllUserRolesList()
{
List<Lib.Dtos.AllUserInRolesDto> allUsers = _userBL.UserAllRolesGet();
return new JsonResult(allUsers);
}
my solution
After taking a step back for a second I realized I actually wasn't returning the right object back to my roles property...and so need to iterate over my roles and create a list from them. Here is what worked.
public List<AllUserInRolesDto> UserAllRolesGet()
{
List<AllUserInRolesDto> getAllUsersRoles = (from u in _Context.Users
join r in _context.UserInRoles on u.UserId equals r.UserId
into ur
select new Lib.Dtos.AllUserInRolesDto()
{
FullName = u.Fullname,
Email = u.Email,
Roles = .Select(x => new Lib.Dtos.RoleDto() { RoleName = x.RoleName }).ToList() //Changed to this
}).ToList();
return getAllUsersRoles;
}
Anyway, probably a pretty dumb mistake, but had me stuck for a bit. Maybe this helps someone in my same position or if someone has a comment of how I could have improved this or used a different approach I am open to hearing suggestions.

Answer 1

I assume you're using Entity Framework, and that you have your DB model defined with relationships. This means you don't need to use explicit JOINs in your queries: you can use navigation properties instead.
Your "business layer" (note that you don't necessarily always need a business layer) should only work with Entity types and should not use DTOs (as DTOs belong to your web-service, in the same way that View-Models belong to a web-application).
If your "business layer" just consists of predefined queries, I recommend defining them as static extension methods for your DbContext and returning IQueryable<T> instead of as materialized List<T> as this enables your consumers to perform further operations on them (such as additional filtering or sorting and paging).
I recommend doing it like this instead:
// Queries methods (i.e. "business layer" queries)
public static class QueriesExtensions
{
public static IQueryable<User> GetAllUsersAndTheirRoles( this MyDbContext db )
{
// I assume `UserInRoles` is a linking table for a many-to-many relationship:
return db
.UserInRoles
.Include( uir => uir.User )
.Include( uir => uir.Role )
.Select( uir => uir.User );
}
}
// Web-service controller:
[HttpGet("GetAllUserRolesList")]
[Produces(typeof(List<AllUserInRolesDto>)]
public async Task<IActionResult> GetAllUserRolesList()
{
List<User> usersList = await this.db
.GetAllUsersAndTheirRoles()
.ToListAsync();
List<Lib.Dtos.AllUserInRolesDto> usersListDto = usersList
.Select( u => ToDto( u ) )
.ToList();
return new JsonResult( usersListDto );
}
// Entity-to-DTO mapping functions (if you have a lot of DTOs and entities, consider using AutoMapper to reduce the tedium)
private static AllUserInRolesDto ToDto( User user )
{
return new AllUserInRolesDto()
{
FullName = user.FullName,
Email = user.Email,
Roles = user.Roles.Select( r => ToDto( r ) ).ToList()
};
}
private static RoleDto ToDto( Role role )
{
return new RoleDto()
{
RoleName = role.RoleName
};
}