Most efficient method of self referencing tree using Entity Framework

Question

So I have a SQL table which is basically

ID, ParentID, MenuName, [Lineage, Depth]

The last two columns are auto-computed to help with sear

Answer 1

I knew that there must be something wrong with this solution. It is not simple. Using this solution, EF6 require another package of hacks to manage a simple tree (fe. deletions). So finally I've found a simple solution but combined with this approach.

First of all leave entity simple: just Parent and list of Children is enough. Also mapping should be simple:

 HasOptional(x => x.Parent)
    .WithMany(x => x.Children)
    .Map(m => m.MapKey("ParentId"));

 HasMany(x => x.Children)
    .WithOptional(x => x.Parent);

Then add migration (code first: migrations: package console: Add-Migration Hierarchy) or in other ways a stored procedure:

CREATE PROCEDURE [dbo].[Tree_GetChildren] (@Id int) AS
BEGIN
WITH Hierachy(ChildId, ParentId) AS (
    SELECT ts.Id, ts.ParentId 
        FROM med.MedicalTestSteps ts
    UNION ALL 
    SELECT h.ChildId, ts.ParentId 
        FROM med.MedicalTestSteps ts
        INNER JOIN Hierachy h ON ts.Id = h.ParentId
) 
SELECT h.ChildId
    FROM Hierachy h
    WHERE h.ParentId = @Id
END

Then when you will try to receive your tree nodes from database just do it in two steps:

//Get children IDs
var sql = $"EXEC Tree_GetChildren {rootNodeId}";
var children = context.Database.SqlQuery(sql).ToList();

//Get root node and all it's children
var rootNode = _context.TreeNodes
                    .Include(s => s.Children)
                    .Where(s => s.Id == id || children.Any(c => s.Id == c))
                    .ToList() //MUST - get all children from database then get root
                    .FirstOrDefault(s => s.Id == id);

It all. This query helps you to get a root node and load all children. Without playing with introducing Ancestors and Descendants.

Remember also when you will try to save sub-node, then do it just this way:

var node = new Node { ParentId = rootNode }; //Or null, if you want node become a root
context.TreeNodess.Add(node);
context.SaveChanges();

Do it that way, not by adding children to root node.