C# Table Per Hierarchy Projection Union RRS feed

  • Question

  • I'm using table per hierarchy to project to model classes. When I use of type in Linq to Entities, all of my results are always the last type which was projected. What I mean is if I have these for domain models:

    public interface IPerson { string Name {get;set;} }
    public abstract class Person : IPerson { public string Name { get;set; } }
    public class Employee : Person{ }
    public class Manager : Person { }
    And I have a Person table with a Name and type column, and use table per hierarchy to yield me specific Entities (which I'll refer to as EmployeeEntity and ManagerEntity).

    When I use this code:

    IQueryable<IPerson> people = entities.OfType<ManagerEntity>().Select(x => new Manager 
    { Name = }).Concat(entities.OfType<EmployeeEntity>().Select(y => new Employee
    { Name = }));

    var projectedPeople = people.ToList();

    All of the types of objects in projectedPeople are Employee, even the the objects that should be of type Manager. If I remove the Concat call and run them individually, I get the correct type back (Manager or Employee).

    What am I doing wrong here? I wrote some test code that removed Linq from the equation by making dummy lists of objects and calling AsQueryable on them, followed by a projection, and that worked as it should. I've found that
    if I call ToList on the Manager Select (entities.OfType<ManagerEntity>().Select(x => new Manager { Name = })).ToList(), then it initializes the appropriate type of object correctly.
    Thursday, June 6, 2013 12:54 PM

All replies

  • Hi Robert,

    Thanks for your post.

    However I'm not able to get it work using your code:

    IQueryable<IPerson> people = entities.OfType<ManagerEntity>().Select(x => new Manager 
     { Name = }).Concat(entities.OfType<EmployeeEntity>().Select(y => new Employee
     { Name = }));

    I always get a compile-time error. According to the definition of the Concat extension method, the two sequences should have the same type(TSource). I think we cannot concatenate two sequences with different types.

    However, you may have a look at this thread about how to concat two different IQueryable<T>:

    Best regards,

    Chester Hong
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    Tuesday, June 11, 2013 1:39 AM
  • Hi Chester, 

    Thanks for your reply. I just typed this code up on a whim off my head as I don't want to paste my production code in - I have something similar compiling and running, but always returning 1 type instead of the correct types. It shouldn't be concating 2 different types because they're both being projected to types that implement IPerson. Try adding the type parameter of IPerson on your Concat call - I.E (both Manager and Employee are of type IPerson). I'm starting to wonder if it's a problem with the Entity Framework Queryable provider.

    IQueryable<IPerson> people = entities.OfType<ManagerEntity>().Select(x => new Manager 
     { Name = }).Concat<IPerson>(entities.OfType<EmployeeEntity>().Select(y => new Employee
     { Name = }));
    Friday, June 14, 2013 2:46 AM