Entity Framework: Inheritance and Include

Question

Assume the following hierarchy:

class Department { EntityCollection<Employee> Employees; } class Employee { string Name; } class RemoteEmployee : Employee { Country Location; EntityReference<Country> CountryReference; }

So, department contains a list of employees. There is a hierarchy of employee types, some types reference other entities. Let's suppose we need to load department with its employees. OK, not a problem:

dataContext.Departments.Include("Employees")

This returns concrete employee types (i.e. RemoteEmployee for Remote ones). Now we need to load Location with Remote employees.

dataContext.Departments.Include("Employees").Include("Employees.Location") - Error: no such property in Employee dataContext.Departments.Include("Employees").Include("RemoteEmployees.Location") - Error: no such property in Department

What should I specify in Include to load Location with RemoteEmployee?

What's wrong with ALex's solution. Why don't you accept it so he can get reward from it ? — VdesmedT
– VdesmedT, Commented Jun 4, 2011 at 5:14

Alex James · Accepted Answer · 2009-06-04 00:39:21Z

I'm pretty sure what CatZ suggests doesn't work.

I don't think you can do this using Include, but you can achieve the same effect using a projection trick see this How to Sort Relationships in the Entity Framework

What you need to do is something like this:

var results = from d in ctx.Departments select new { d, employees = d.Employees.Select( e => new { e, location = e is RemoteEmployee ? (e as RemoteEmployee).Location : null } ) }; foreach (var result in results) { var re = result.d.Employees.First() as RemoteEmployee; Console.WriteLine("{0} {1} works from {2}", re.Firstname, re.Surname, re.Location.Name); }

Notice that you don't need to use the anonymous types to get the data, essentially doing the projection has a side-effect of filling the collections on you department because of a feature of the Entity Framework called fixup.

Hope this helps Alex

Thanks, that helps. I can't say I'm happy with this solution. Now I just manually load required properties using this: department.Employees.OfType<RemoteEmployee>.ForEach(re => re.LocationReference.Load()); It seems like more readable but at the speed cost.
I am trying to implement the above solution, but in the above example where you have d.Employees.Select( my navigation property is not a collection because of the multiplicity, so it does not have a Select( method. If it was instead a single employee like d.Employee and I wanted to check and see if Employee was a certain derived type, and if so then load it's navigation properties.

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