实体框架代码优先于隐含组合键的可选一对多关系

Question

Update : Created a sample project on GitHub.

In my existing database I have a generic audit table that has no keys, but I'd like to insert into this audit table with EF code first.

Existing reports pull audits based on AffectedId and EntityId where EntityId is hardcoded in a bunch of places.
I reversed engineered the database, but there is no explicit relationship between these tables...so here are the base POCO objects (I can't make a relationship either, its an existing system)

public class Audit
{
    public int Id { get; set; }
    public int EntityId { get; set; }
    public string AffectedId { get; set; }       
    public string NewValue { get; set; }
}

public class Action1
{
    public int Id { get; set; }
    public string Desc { get; set; }
}   

public class Action2
{
    public int Id { get; set; }
    public string Desc { get; set; }
}

I think I want the POCO objects to look like this

public class Audit
{
    public int Id { get; set; }
    public int EntityId { get; set; }
    public string AffectedId { get; set; }       
    public string NewValue { get; set; }
    public virtual Action1 Action1 { get; set; } // but I don't want this to change audit table
    public virtual Action2 Action2 { get; set; } // but I don't want this to change audit table
}

public class Action1
{
    public Action1() {this.Audits = new List<Audit>();}
    public int Id { get; set; }
    public string Desc { get; set; }
    public virtual ICollection<Audit> Audits { get; set; }
}   

public class Action2
{
    public Action2() {this.Audits = new List<Audit>();}
    public int Id { get; set; }
    public string Desc { get; set; }
    public virtual ICollection<Audit> Audits { get; set; }
}

But I can't seem to get the fluent mapping to allow me to insert an Action (1 or 2) that has populated AffectedId's in the Audit. This is what I was thinking on the mapping objects, but can't seem to get the hardcoded EntityId key to work correctly.

public class AuditMap : EntityTypeConfiguration<Audit>
{
    public AuditMap()
    {
        // Primary Key
        this.HasKey(t => t.Id);


        this.HasOptional(t => t.Action1)
            .WithMany(t => t.Audits)
            .HasForeignKey(t => new {EntityId = 3, AffectedId = t.Id});

        this.HasOptional(t => t.Action2)
            .WithMany(t => t.Audits)
            .HasForeignKey(t => new {EntityId = 5, AffectedId = t.Id});
    }
}

public class Action1 : EntityTypeConfiguration<Action1>
{
    public Action1Map()
    {
        // Primary Key
        this.HasKey(t => t.Id);
    }
}

public class Action2 : EntityTypeConfiguration<Action2>
{
    public Action2Map()
    {
        // Primary Key
        this.HasKey(t => t.Id);
    }
}

Any suggestions on how to change the C# and not the SQL would be appreciated.

Answer 1

Mapping will not handle this scenario, but you can modify your domain model and business rules to do so. And having an enum for your magic values for EntityId will be much better.

public class Audit
{
    public int Id { get; set; }
    public int EntityId { get; set; }
    public string AffectedId { get; set; }       
    public string NewValue { get; set; }
}

public abstract class AuditableAction{

    public AuditableAction() {this.Audits = new List<Audit>();}

    public int Id { get; set; }
    public string Desc { get; set; }
    public virtual IList<Audit> Audits { get; set; }

    public void Audit(string description){
        this.Audits.Add(new Audit(){
            EntityId = this.GetEntityId(),
            AffectedId = this.Id,
            NewValue = description
        });
    }

    public abstract int GetEntityId();
}

public class Action1 : AuditableAction
{
    public override int GetEntityId(){
        return AuditCode.Magic3.GetHashCode();
    }
}   

public class Action2 : AuditableAction
{
    public override int GetEntityId(){
        return AuditCode.Magic5.GetHashCode();
    }
}

public enum AuditCode{
    Magic3 = 3,
    Magic5 = 5
}

Usage based on GitHub code dump

using (var context = new yunoworkContext())
{
    var a = new Action1() {Id = 4, Desc = Guid.NewGuid().ToString()};

    // This audit should insert an audit with EntityId = 3 and AffectedId = {primary key of the assiciated Action1}
    a.Audit("Console!");
    context.SaveChanges();
}