How does Entity Framework work with recursive hierarchies? Include() seems not to work with it

Question

I have an Item. Item has a Category.

Category has ID, Name, Parent

Answer 1

Use this extension method which calls the hard-coded version of Include, to achieve a dynamic depth level of inclusion, it works great.

namespace System.Data.Entity
{
  using Linq;
  using Linq.Expressions;
  using Text;

  public static class QueryableExtensions
  {
    public static IQueryable Include(this IQueryable source,
      int levelIndex, Expression> expression)
    {
      if (levelIndex < 0)
        throw new ArgumentOutOfRangeException(nameof(levelIndex));
      var member = (MemberExpression)expression.Body;
      var property = member.Member.Name;
      var sb = new StringBuilder();
      for (int i = 0; i < levelIndex; i++)
      {
        if (i > 0)
          sb.Append(Type.Delimiter);
        sb.Append(property);
      }
      return source.Include(sb.ToString());
    }
  }
}

Usage:

var affiliate = await DbContext.Affiliates
  .Include(3, a => a.Referrer)
  .SingleOrDefaultAsync(a => a.Id == affiliateId);

Anyway, meanwhile, join the discussion about it on the EF repo.