CODEWITHSUNDEEP
c#linq
Kabi
Kabi

Reputation: 2045

Linq query results to List collection

I use the code below to get records from two tables but I want to have the result in a List. I used the code below, but this error occured:

Cannot implicitly convert type System.Collections.Generic.List<AnonymousType#1> to System.Collections.Generic.List<QuickRoutes.DAL.Route>

public List<Route> GetAllForUser(Guid userId)
{
    // var result = new List<Route>();
    aspnetdbDataContext aspdb = new aspnetdbDataContext();
    List<Route> result  = (from r in aspdb.Routes
                where r.UserId == userId
                join t in aspdb.TrackPoints on r.RouteId equals t.RouteFK
                select t.TrackPointId,t.RouteFK,t.TrackTime,t.Longitude,t.Latitude,t.Elevation, r.SourceName).ToList();
    return result;
}

EDIT:

I want to match my query with this class:

namespace QuickRoutes.Entities
{
    public enum RouteType
    {
        Route, Waypoints, Track
    }

    public sealed class Route
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public DateTime Time { get; set; }
        public List<TrackPoint> TrackPoints { get; set; }
        public Guid UserId { get; set; }
        public string GpxData { get; set; }
        public RouteType RouteType { get; set; }


        public Route(int id)
        {
            Id = id;
            TrackPoints = new List<TrackPoint>();
        }
......

but if I change my code to this one,It doesn't work too

List<Route> result = (from r in aspdb.RouteLinqs
                                  where r.UserId == userId
                                  join t in aspdb.TrackPointlinqs on r.RouteId equals t.RouteFK
                                  select r).ToList();

to be honest I want to change this function that is written with SQL to LINQ,have any better idee?

namespace QuickRoutes.Entities
{
    public enum RouteType
    {
        Route, Waypoints, Track
    }

    public sealed class Route
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public DateTime Time { get; set; }
        public List<TrackPoint> TrackPoints { get; set; }
        public Guid UserId { get; set; }
        public string GpxData { get; set; }
        public RouteType RouteType { get; set; }


        public Route(int id)
        {
            Id = id;
            TrackPoints = new List<TrackPoint>();
        }
......

Upvotes: 2

Views: 9345

Answers (3)

Dinesh
Dinesh

Reputation: 3770

I have faced the same. The issue here is that you are creating an anonymous type that contains fields from both the Route and aspdb.TrackPoints.

Hence you cannot cast this to List.

This is a mapping problem. To resolve this you need to create a newcustom class that contains all the fields/properties that you are getting out from the query.

Let's say you create a custom class say RouteMapper then map using code like

select new RouterMapper
{
     RouteMapper.TrackPointId = t.TrackPointId, RouteMapper.RouteFK=t.RouteFK,    RouteMapper.SourceName = r.SourceName
}

This way now you return List< RouteMapper>.

Upvotes: 1

Adi Lester
Adi Lester

Reputation: 25201

Since your query selects properties from two different tables, it obviously no longer returns objects of type Route, but a new type of object (an anonymous type).

If you want to return this new type, you need to define it explicitly, then return the data using this type.

public class MyClass
{
    public MyClass(int trackPointId, DateTime trackTime, ...)
    {
        TrackPointId = trackPointId;
        TrackTime = trackTime;
        ...
    }


    public int TrackPointId { get; set; }
    public DateTime TrackTime { get; set }
    ...
}

List<MyClass> result  = (from r in aspdb.Routes
              where r.UserId == userId
              join t in aspdb.TrackPoints on r.RouteId equals t.RouteFK
              select new MyClass(t.TrackPointId,t.RouteFK,t.TrackTime,t.Longitude,t.Latitude,t.Elevation, r.SourceName);

Upvotes: 1

Dave Bish
Dave Bish

Reputation: 19646

It's because your projection (what you're selecting) isn't the same as a Route (what you're trying to return);

If you wish to return a Route Change your select to:

select r

If you wish to return your joined projection, you'l have to create a new type, and return that:

e.g:

public class RouteTrack
{
    public TrackPointId ...
    public RouteFK ...
    public TrackTime ...
}

And return a List<RouteTrack> from your method, and change your select to:

select new RouteTrack { TrackPointId = t.TrackPointId .... }

Upvotes: 2

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