DbSet include extension method looping - linq

Question

I've added the following extension method
/// <summary>
/// Provides a statically typed interface for db includes
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="set">The set.</param>
/// <param name="includes">The includes.</param>
/// <returns>DbSet<T>.</returns>
public static DbSet<T> Include<T>(this DbSet<T> set, params Expression<Func<T, object>>[] includes) where T : class
{
if (includes != null)
{
foreach (var expression in includes)
{
set.Include(expression);
}
}
return set;
}
This is based on the repository code I found here
https://github.com/carbonrobot/FullStackEF/tree/master/src
However, when I utilise this with the following
public ServiceResponse<Town> Get(int id)
{
Func<Patient> func = delegate
{
using (var context = _contextFactory())
{
return context.Get<Town>(id, x => x.County);
}
};
return this.Execute(func);
}
Where the town class contains a County entity.
I am getting a infinite loop as its calling the extension method rather than the base include?
Any ideas what I am doing wrong here?

Answer 1

There a several mistakes in that method.
The DbExtensions.Include method has the following signature:
public static IQueryable<T> Include<T, TProperty>(
this IQueryable<T> source,
Expression<Func<T, TProperty>> path
)
where T : class
As you can see, it receives IQueryable<T> and returns another IQueryable<T> which has to be assigned to a variable and returned instead of the original in order to has effect, which the code is not doing.
Also, since the method calls Include on the set variable of type DbSet<T> which is more concrete than the IQueryable<T>, and the argument matches the signature of the custom method, the compiler simply calls the same method, hence the StackOverflowException.
With that being said, here is the correct custom method signature and implementation:
public static IQueryable<T> Include<T>(this DbSet<T> set, params Expression<Func<T, object>>[] includes)
where T : class
{
var result = set.AsQueryable();
if (includes != null)
{
foreach (var expression in includes)
{
result = result.Include(expression);
}
}
return result;
}