Question

An existing DB schema has unique, non-primary, keys, and some foreign keys that rely on them.

Is it possible to define unique keys, which are not primary keys, in Entity Framework v4? How?

Answer 1

I’ve tried defining the following tables:

• Orders [Id (primary, identity), ClientName, FriendlyOrderNum (unique)]
• OrderItems [Id (primary, identity), FriendlyOrderNum (unique), ItemName]

And a foreign key mapping from OrderItems.FriendlyOrderNum (Mant) to Orders.FriendlyOrderNum (one).

If unique non-primary keys are possible the following SSDL should work:

<Schema Namespace="EfUkFk_DbModel.Store" Alias="Self" Provider="System.Data.SqlClient" ProviderManifestToken="2008" xmlns:store="http://schemas.microsoft.com/ado/2007/12/edm/EntityStoreSchemaGenerator" xmlns="http://schemas.microsoft.com/ado/2009/02/edm/ssdl">
    <EntityContainer Name="EfUkFk_DbModelStoreContainer">
      <EntitySet Name="OrderItems" EntityType="EfUkFk_DbModel.Store.OrderItems" store:Type="Tables" Schema="dbo" />
      <EntitySet Name="Orders" EntityType="EfUkFk_DbModel.Store.Orders" store:Type="Tables" Schema="dbo" />
    </EntityContainer>
    <EntityType Name="OrderItems">
      <Key>
        <PropertyRef Name="RowId" />
      </Key>
      <Property Name="RowId" Type="bigint" Nullable="false" StoreGeneratedPattern="Identity" />
      <Property Name="OrderNum" Type="char" Nullable="false" MaxLength="5" />
      <Property Name="ItemName" Type="varchar" MaxLength="100" />
    </EntityType>
    <!--Errors Found During Generation:
  warning 6035: The relationship 'FK_OrderItems_Orders' has columns that are not part of the key of the table on the primary side of the relationship. The relationship was excluded.
  -->
    <EntityType Name="Orders">
      <Key>
        <PropertyRef Name="RowId" />
      </Key>
      <Property Name="RowId" Type="bigint" Nullable="false" StoreGeneratedPattern="Identity" />
      <Property Name="ClientName" Type="varchar" MaxLength="100" />
      <Property Name="OrderNum" Type="char" Nullable="false" MaxLength="5" />
    </EntityType>

  <!-- AsafR -->
    <Association Name="FK_OrderItems_Orders">
      <End Role="Orders" Type="EfUkFk_DbModel.Store.Orders" Multiplicity="1">
      </End>
      <End Role="OrderItems" Type="EfUkFk_DbModel.Store.OrderItems" Multiplicity="*" />
      <ReferentialConstraint>
        <Principal Role="Orders">
          <PropertyRef Name="OrderNum" />
        </Principal>
        <Dependent Role="OrderItems">
          <PropertyRef Name="OrderNum" />
        </Dependent>
      </ReferentialConstraint>
    </Association>
  </Schema></edmx:StorageModels>

It doesn’t. There’s also no possibility for adding more <key> elements in an <EntityType>.

My conclusion is that non-primary unique keys are not support in EF 4.