Entity Framework: How to use Entity Splitting with different PK?
Imagine you want to create an application which manages product stocks using Northwind but which doesn’t create products.
For this, we want two Entitysets: Product and Supplier with Supplier on read only.
We also want a read only product CategoryName property.
How to do this with the least possible amount of work?
To begin with, we will change all Supplier properties set visibility to private. For this, we will modify xml Setter attribute.
Of course, we can do this with EDM designer properties Window (from VS 2008 SP1 Beta).
Then, we will also change the Supplier Product property Setter visibility to private and change the Products Supplier property (get + set) visibility to private.
Next, we will remove Product CategoryID property.
At this point, you should have this csdl:
<!-- CSDL content -->
<edmx:ConceptualModels>
<Schema Namespace="NorthwindEFModel" Alias="Self" xmlns="http://schemas.microsoft.com/ado/2006/04/edm">
<EntityContainer Name="NorthwindEFEntities">
<EntitySet Name="Products" EntityType="NorthwindEFModel.Product" />
<EntitySet Name="Suppliers" EntityType="NorthwindEFModel.Supplier" />
<AssociationSet Name="FK_Products_Suppliers" Association="NorthwindEFModel.FK_Products_Suppliers">
<End Role="Suppliers" EntitySet="Suppliers" />
<End Role="Products" EntitySet="Products" />
</AssociationSet>
</EntityContainer>
<EntityType Name="Product">
<Key>
<PropertyRef Name="ProductID" />
</Key>
<Property Name="ProductID" Type="Int32" Nullable="false" />
<Property Name="ProductName" Type="String" Nullable="false" MaxLength="40" Unicode="true" FixedLength="false" />
<Property Name="QuantityPerUnit" Type="String" MaxLength="20" Unicode="true" FixedLength="false" />
<Property Name="UnitPrice" Type="Decimal" Precision="19" Scale="4" />
<Property Name="UnitsInStock" Type="Int16" />
<Property Name="UnitsOnOrder" Type="Int16" />
<Property Name="ReorderLevel" Type="Int16" />
<Property Name="Discontinued" Type="Boolean" Nullable="false" />
<NavigationProperty Name="Supplier" Relationship="NorthwindEFModel.FK_Products_Suppliers" FromRole="Products" ToRole="Suppliers" a:SetterAccess="Private" xmlns:a="http://schemas.microsoft.com/ado/2006/04/codegeneration" />
</EntityType>
<EntityType Name="Supplier">
<Key>
<PropertyRef Name="SupplierID" />
</Key>
<Property Name="SupplierID" Type="Int32" Nullable="false" />
<Property Name="CompanyName" Type="String" Nullable="false" a:SetterAccess="Private" xmlns:a="http://schemas.microsoft.com/ado/2006/04/codegeneration" />
<Property Name="ContactName" Type="String" Nullable="true" a:SetterAccess="Private" xmlns:a="http://schemas.microsoft.com/ado/2006/04/codegeneration" />
<Property Name="ContactTitle" Type="String" Nullable="true" a:SetterAccess="Private" xmlns:a="http://schemas.microsoft.com/ado/2006/04/codegeneration" />
<Property Name="Address" Type="String" Nullable="true" a:SetterAccess="Private" xmlns:a="http://schemas.microsoft.com/ado/2006/04/codegeneration" />
<Property Name="City" Type="String" Nullable="true" a:SetterAccess="Private" xmlns:a="http://schemas.microsoft.com/ado/2006/04/codegeneration" />
<Property Name="Region" Type="String" Nullable="true" a:SetterAccess="Private" xmlns:a="http://schemas.microsoft.com/ado/2006/04/codegeneration" />
<Property Name="PostalCode" Type="String" Nullable="true" a:SetterAccess="Private" xmlns:a="http://schemas.microsoft.com/ado/2006/04/codegeneration" />
<Property Name="Country" Type="String" Nullable="true" a:SetterAccess="Private" xmlns:a="http://schemas.microsoft.com/ado/2006/04/codegeneration" />
<Property Name="Phone" Type="String" Nullable="true" a:SetterAccess="Private" xmlns:a="http://schemas.microsoft.com/ado/2006/04/codegeneration" />
<Property Name="Fax" Type="String" Nullable="true" a:SetterAccess="Private" xmlns:a="http://schemas.microsoft.com/ado/2006/04/codegeneration" />
<Property Name="HomePage" Type="String" Nullable="true" a:SetterAccess="Private" xmlns:a="http://schemas.microsoft.com/ado/2006/04/codegeneration" />
<NavigationProperty Name="Products" Relationship="NorthwindEFModel.FK_Products_Suppliers" FromRole="Suppliers" ToRole="Products" a:SetterAccess="Private" xmlns:a="http://schemas.microsoft.com/ado/2006/04/codegeneration" a:GetterAccess="Private" />
</EntityType>
<Association Name="FK_Products_Suppliers">
<End Type="NorthwindEFModel.Supplier" Role="Suppliers" Multiplicity="0..1" />
<End Type="NorthwindEFModel.Product" Role="Products" Multiplicity="*" />
</Association>
</Schema>
</edmx:ConceptualModels>
Now, we just need to add Product CategoryName property.
How to do this? We can use a SQL view instead of Products table and use stored procedures for CUD operations. In the same way, we can also use ssdl view with ssdl functions (for more information, look at my EDM article). However, we want to do the least possible amount of work and, on this purpose, we can use a better approach.
We will define a partial ssdl view and we will use EntitySplitting to keep the Product part already generated by designer. With this approach, we won’t have to define ssdl CUD functions because we suppose Product CategoryName property is read only.
To do this, in SSDL part, we will define a new EntitySet:
<EntitySet Name="ProductCategoryName" EntityType="NorthwindEFModel.Store.ProductCategoryName">
<DefiningQuery>
SELECT P.ProductID, C.CategoryName
FROM Products AS P
INNER JOIN Categories as C ON C.CategoryID = P.CategoryID
</DefiningQuery>
</EntitySet>
And a new EntityType (also in SSDL):
<EntityType Name="ProductCategoryName">
<Key>
<PropertyRef Name="ProductID" />
</Key>
<Property Name="ProductID" Type="int" Nullable="false" StoreGeneratedPattern="Identity" />
<Property Name="CategoryName" Type="nvarchar" MaxLength="15" />
</EntityType>
Now, we can back to designer and add CategoryName Product property (of type string with setter private) and do EntitySplitting on Product EntityType.
That’s all, folks! 
You have a read only EntityType Supplier and an EntityType Product with a read only CategoryName property.
Isn’t it too easy to use Entity Framework?