model如何在EDMX中建立非标准关系？

Question

I'm trying to model a somewhat non-standard relationship using .NET Entity Framework 4 for consumption over a RESTful WCF Data Service.

Consider the following simplified data structure where metadata is stored in a single table, but may be associated to different entities stored in different tables (identified by the TYPE column)

METADATA Table
--------------
ID      FK_ID   TYPE        VALUE
--      ----    -----       -----
1       100     PRODUCT     Foo
2       101     PRODUCT     Foo
3       101     SERVICE     Bar
4       102     SERVICE     Bar

PRODUCT Table
-------------
ID      Name
--      ----
100     A
101     B
102     C
103     D

SERVICE Table
-------------
ID      Name
--      ----
100     W
101     X   
102     Y
103     Z

The problem I am facing is that I want to create a property

Product.List<Metadata> 

for the Product object and the Service object. Since they are not associated with a single FK to a single table I don't know how I can model this relationship in an EDMX file.

My end goal is to be able to call a method on a WCF Data Service, and return a JSON response that has a Product serialized with a list of its Metadata included.

Answer 1

One way to do this would be to create either a computed column or a view with an additional column for each of the tables that has metadata and populate the additional column with the name of the table.

CREATE VIEW PRODUCT_VIEW AS
    Select ID, Name, "PRODUCT" as Type From PRODUCT

Or

CREATE TABLE PRODUCT(
  ID int,
  Name varchar(20),
  Type AS "PRODUCT"
)

Then you can have a FK relationship between PRODUCT_VIEW/PRODUCT and METADATA on the fields FK_ID and Type. These two fields could then be mapped as a complex type and a relationship between the METADATA table and PRODUCT_VIEW can be formed in EF.