not getting child category when returning parent category in linq entity framework - linq

Question

I want to return the parent category along with the subcategory. There is a self join in my table. This is my class:
public partial class CategoryMaster
{
public int Id { get; set; }
public string Name { get; set; }
public Nullable<int> ParentId { get; set; }//parentid is link to Id
public virtual ICollection<CategoryMaster> CategoryMaster1 { get; set; }
public virtual CategoryMaster CategoryMaster2 { get; set; }
}
I use this query to return the parent category and the child category:
var GetallCategories = context.CategoryMaster.Include("CategoryMaster1")
.Where(d => d.ParentId == null)
.OrderBy(d => d.Name)
.Select(d => new SelectListItem { Text = d.Name,
Value = d.Id.ToString()
})
.ToList();
The problem is that it is just returning parent category. Whats wrong with my query?

Answer 1

The first problem is your where clause. You told it to ONLY bring back CategoryMasters with a null parent. So you won't get any children out of the DB.
We have a more rigid (read: slower) pattern we follow where I work with our EF queries, so I've never done exactly what you're doing here, but I think all you have to do is move the where clause, like this:
var GetallCategories = context.CategoryMaster.Include("CategoryMaster1")
.OrderBy(d => d.Name)
.ToList();
.Where(d => d.ParentId == null)
.Select(d => new SelectListItem { Text = d.Name,
Value = d.Id.ToString()
})
The ToList forces a DB call and then the where and select after it get processed after it comes back from the DB, at which point, it's gotten all the data with no where clause. If I understand correctly, you do want all the data, you just want your list to contain only the parents at the top level and then drill down to get to the children.
So if you add any where clause before the tolist, it's going to restrict what comes back from the DB before it even tries to build the hierarchy of objects. If you look at the actual sql generated by EF, you can see this. This means that if you legitimately need a where clause - say you want to bring back all parents with a lastname of "Smith" plus their children - you have to make it more complex. If you need a meaningful where caluse to filter parents in the DB (which you might for performance) and you have to allow for an unknown number of generations of children, this becomes VERY difficult to do with EF includes.