带有组合键的一对一实体框架代码优先映射

Question

Is it possible to create a one-to-one relationship on already defined entity properties? I've got the following entities:

public class Asset
{
    public int AssetId { get; set; }
    public int OwningCustomerId { get; set; }
    public virtual Customer OwningCustomer { get; set; }
}

public class CustomerAsset
{
    public int CustomerId { get; set; } // Primary key 0
    public int AssetId { get; set; }    // Primary key 1
    public int CustomerAssetStatusId { get; set; }
    public string Name { get; set; }

    public virtual Customer Customer { get; set; }
    public virtual Asset Asset { get; set; }
}

CustomerAsset represents various states of ownership of an asset. Although the same AssetId can exist multiple times in this table, there will only ever be one instance where CustomerAssetStatusId = 1. In order to have quick access to the asset's current owner, I also maintain OwningCustomerId in the Asset table.

I would like to have a navigation property from Asset to CustomerAsset called OwningCustomerAsset. This is a one-to-one relationship. Unfortunately, I don't know how to define it since the foreign key fields are already defined in Asset. Typically, I would create a relationship like this on Asset:

HasRequired(e => e.OwningCustomerAsset).WithRequiredDependent().Map(m => m.MapKey("OwningCustomerId", "AssetId"));

Of course this results in the following error: "Each property name in a type must be unique. Property name 'OwningCustomerId' was already defined."

How can I tell EF that OwningCustomerId/AssetId is the foreign key to CustomerAsset?

Answer 1

If you can modify your schema, I suggest making asset ownership a property of the asset itself and not of the customer-asset relationship. Having a non-nullable FK field from Asset to Customer (eg Owner_CustomerID ) enforces the "one owner only" constraint and the owner can be easily loaded from CustomerAsset.Asset.Owner (or whatever you choose to name it). This schema change will greatly simplify your queries.

Furthermore, this will allow you to add a navigation property to Customer that references all owned assets; Customer.OwnedAssets , for example

Update:

Also add navigation property Asset.OwningCustomerAsset (or whatever you wish) from Asset to CustomerAsset using the new Owner_CustomerID field by way of compound FK ( AssetId, Owner_CustomerId ) and resulting navigation property

Answer 2

Since I came down this road needing a navigation property on the other end (which I don't need anymore), I was stuck with the one-to-one mindset. The following gets me what I want:

HasRequired(e => e.OwningCustomerAsset).WithMany().HasForeignKey(e =>  new { e.OwningCustomerId, e.AssetId });