Question

Quick question that requires a long explanation..

Say I have two tables – one is an item table (say ‘Users’) and another is a definition table – like ‘Custom Properties’. Many different items in the system (‘Users’, ‘Articles’, ‘Posts’, etc) can all have custom property defined to them, and these are stored in the ‘Custom Properties’ table. So, for example, the ‘Custom Properties’ table looks like:

CREATE TABLE [CUSTOMPROP_DEFINITION] (
    [ITEM_TYPE] INTEGER NOT NULL,
    [POSITION] INTEGER NOT NULL,
    [NAME] NVARCHAR(MAX) NOT NULL
)

Simple little table. Each item has a ‘item_type’ id (for example, a user is an item type of 1. Article would be an item type of 2, and so on), so this table could have multiple rows for each item. Essentially, this table’s metadata for the other tables.

I want to create a navigation property on my Users table, that will link to all the entries in the props table where ‘item_type’ == 1.

What’s the best way of going about this? From the way I see it, there are two options –
(1) Creating a navigation property through the EDMX and letting it populate it automagically. (This is preferred, but having troubles implementing..) or

(2) Creating a property in the partial class, and having that load everything manually.

The issue with #2 is that it would (could potentially?) be slower than having the entity framework handle loading.
The issue with #1 is that.. no matter what I try, I can’t get a NavigationProperty defined that will handle it. Because the primary key is a fixed number – i.e. It will always be ‘1’ for ALL Users, always be ‘2’ for all articles, etc.. – I haven’t been able to find a way to hook into that.

Thoughts?
–Mike.

Answer 1

What you’re describing isn’t really a “Navigation Property” in terms of what EF defines as a naviation property. A navigation property in EF terms follows a [usually] primary key – foreign key reference in the database schema itself. And, AFAIK, the only way to get that navigation property in the EDMX is for there to actually be a FK involved.

You could, obviously (and probably do) have a FK here, but that’s not entirely what you want, because that FK is going to return all instances of your custom properties for the given primary key. What you want is instances of only a particular type; and I don’t think there is a “off the shelf” way of doing this in EF.

What you probably want to do is implement a Stored Procedure, and bring that into your model; you could then implement this is a property (or probably more appropriately a method) on your entity.

Alternatively, you could just create the FK, have your entity load all of the custom properties, and then write “helper properties” that do simple LINQ based .Where() filters.