Projecting self referencing multi level Entities In Entity Framework 6

Question

Projecting self referencing multi level entities in Entity Framework 6.

Let\'s say that I have a Category entity as follows:

public clas         


        

Answer 1

I can't say if it's the best or elegant way, but it's pretty standard and efficient non recursive way of building such structure.

Start with loading all categories without parent / child object links using a simple projection:

var allCategories = db.Categories
    .Select(c => new CategoryView
    {
        Id = c.CategoryId,
        ParentCategoryId = c.ParentCategoryId,
        Name = c.Name,
        Description = c.Description,
        ProductCount = c.Products.Count()
    })
    .ToList();

then create a fast lookup data structure for finding CategoryView by Id:

var categoryById = allCategories.ToDictionary(c => c.Id);

then link the subcategories to their parents using the previously prepared data structures:

foreach (var category in allCategories.Where(c => c.ParentCategoryId != null))
{
    category.ParentCategory = categoryById[category.ParentCategoryId.Value];
    category.ParentCategory.SubCategories.Add(category);
}

At this point, the tree links are ready. Depending of your needs. either return the allCategories or the root categories if you need a real tree representation:

return allCategories.Where(c => c.ParentCategoryId == null);

P.S. Actually the allCategories list can be avoided, since categoryById.Values could serve the same purpose.