Question

As it stands now, the CLR UDTs including HierarchyID aren’t supported in Entity Framework 4. HierarchyID.ToString() is useful, but breaks down once any item has 10+ siblings (the basic structure is /3/4/12/ or /3/4/2/ so the 12th node will sort before the 2nd node).

A little more about potential options:

• Bring back hierarchyID as a varbinary and implement my own binary sorter

• Bring back hierarchyID as a varbinary and implement my own hierarchyID.ToString() method which pads the numbers with zeros while building the string so the resulting string is sortable (i.e. “/0003/0004/0012/”). I disassebled Microsoft.SqlServer.Types.dll and looked at the implementation. It looks like the interals are based of a class called “OrdTree” and I could use that class as a basis for re-implementation.

• Write my own CLR type for SQL to work on the binary data and build its own string (a variation of option 2). Although, comes with an added deployment headache.

• Write a SQL udf to parse the hierarchy string and pad it on the DB layer. The lack of array processing/regex’s seems like the biggest issue here.

• Sort by hierarchyID on the database layer and use the ROW_NUMBER() function as a stand in for sort order.

• Write some helper methods on the .net layer which re-parse the hierarchyId.ToString() and generate a sortable string (i.e. “/0003/0004/0012/”).

So my question is has anyone worked around the limitation? Did you use any of the above strategies? If so, how?

Answer 1

Well, I seem to be getting views but no responses. I had some immediate needs to work with the hierarchy structure above SQL, so i put together a static helper class. I don’t consider this a complete solution, but so far it works relatively well. PadPath is really the critical function here.

public static class SQLHierarchyManipulatin {
    const int   DEFAULT_PAD_LEN     = 3;
    const char  DEFAULT_PAD_CHAR    = '0';

    public static string PadPath(string Hierarchy) {
        return PadPath (Hierarchy, DEFAULT_PAD_LEN);
    }       
    public static string PadPath(string Hierarchy, int padLen) {
        string[]    components  = Hierarchy.Split('/');

        for (var i = 0; i < components.Length; i++ ) {
            if (components[i] != "") {
                components[i] = components[i].PadLeft(padLen, DEFAULT_PAD_CHAR);
            }
        }
        return string.Join("/", components);
    }

    public static int CurrentNodeIndex(string Hierarchy) {
        string[]    components  = Hierarchy.Split('/');
        string      startItem   = components[components.Length - 2]; //one slot back from trailing slash

        return int.Parse(startItem);
    }

    public static string ParentPath (string Hierarchy) {
        return  Hierarchy.Substring(0, Hierarchy.TrimEnd('/').LastIndexOf('/') + 1);
    }

    public static string AppendChildWithPadding (string Hierarchy, int childIndex, int padLen) {
        return AppendChild(Hierarchy, childIndex, DEFAULT_PAD_LEN);
    }
    public static string AppendChildWithPadding (string Hierarchy, int childIndex) {
        return AppendChild(Hierarchy, childIndex, DEFAULT_PAD_LEN);
    }
    public static string AppendChild (string Hierarchy, int childIndex) {
        return AppendChild(Hierarchy, childIndex, DEFAULT_PAD_LEN);
    }
    public static string AppendChild (string Hierarchy, int childIndex, int padLen) {
        return Hierarchy + childIndex.ToString().PadLeft(padLen, DEFAULT_PAD_CHAR) + "/";
    }
}

Hope this helps someone! Although, I’d still like to hear from people.