[c#] Return list using select new in LINQ

This is my method which gives me error.

public List<Project> GetProjectForCombo()
{
    using (MyDataContext db = new MyDataContext (DBHelper.GetConnectionString()))
    {
        var query = from pro in db.Projects
                    select new { pro.ProjectName, pro.ProjectId };

        return query.ToList();
    }
}

If i change it with this:

public List<Project> GetProjectForCombo()
{
    using (MyDataContext db = new MyDataContext (DBHelper.GetConnectionString()))
    {
        var query = from pro in db.Projects
                    select pro;

        return query.ToList();
    }
}

Then it works fine with no errors.

Can you please let me know that how I can return only ProjectId and ProjectNam?

You can do it as following:

class ProjectInfo
{
    public string Name {get; set; }
    public long Id {get; set; }

    ProjectInfo(string n, long id)
    {
        name = n;   Id = id;
    }
}

public List<ProjectInfo> GetProjectForCombo()
{
    using (MyDataContext db = new MyDataContext (DBHelper.GetConnectionString()))
    {
         var query = from pro in db.Projects
                    select new ProjectInfo(pro.ProjectName,pro.ProjectId);

         return query.ToList<ProjectInfo>();
    }
}

Your method's return value has to be a List<Project>.

Using select new you are creating an instance of an anonymous type, instead of a Project.

try this solution for me its working

     public List<ProjectInfo> GetProjectForCombo()
      {
    using (MyDataContext db = new MyDataContext 
    (DBHelper.GetConnectionString()))
         {
        return  (from pro in db.Projects
                    select new { query  }.query).ToList();
        }
      }

public List<Object> GetProjectForCombo()
{
   using (MyDataContext db = new MyDataContext (DBHelper.GetConnectionString()))
   {
     var query = db.Project
     .Select<IEnumerable<something>,ProjectInfo>(p=>
                 return new ProjectInfo{Name=p.ProjectName, Id=p.ProjectId);       

     return query.ToList<Object>();
   }

}

You're creating a new type of object therefore it's anonymous. You can return a dynamic.

public dynamic GetProjectForCombo()
{
    using (MyDataContext db = new MyDataContext (DBHelper.GetConnectionString()))
    {
        var query = from pro in db.Projects
                select new { pro.ProjectName, pro.ProjectId };

        return query.ToList();
    }
}

What is being returned is an anonymous type so create a new class with 2 fields

class BasicProjectInfo {
   string name;
   string id;
}

and return new BasicProjectInfo(pro.ProjectName, pro.ProjectId);. You method in this case will return a List<BasicProjectInfo>

public List<Object> GetProjectForCombo()
{
    using (MyDataContext db = new MyDataContext (DBHelper.GetConnectionString()))
     {
         var query = from pro in db.Projects
                     select new {pro.ProjectName,pro.ProjectId};

         return query.ToList<Object>();
    }
}

You cannot return anonymous types from a class... (Well, you can, but you have to cast them to object first and then use reflection at the other side to get the data out again) so you have to create a small class for the data to be contained within.

class ProjectNameAndId
{
    public string Name { get; set; }
    public string Id { get; set; }
}

Then in your LINQ statement:

select new ProjectNameAndId { Name = pro.ProjectName, Id = pro.ProjectId };