Abstract domain model base class when using EntityTypeConfiguration<T>

Question

Is there some trick to getting a central mapping of Base object properties? Is there some simple pattern for abstract classes when using EntityTypeConfiguration.
ANy tips much appreciated. Im unable to declare a class

Public class BaseEntityConfig<T> : EntityTypeConfiguration<T>

Similar issues, where i couldnt get the answers to work How to create and use a generic class EntityTypeConfiguration<TEntity> and Dynamic way to Generate EntityTypeConfiguration : The type 'TResult' must be a non-nullable value type

public  abstract class BosBaseObject
{
  public virtual Guid Id { set; get; }
  public virtual string ExternalKey { set; get; }
  public byte[] RowVersion { get; set; }
}
  public class News : BosBaseObject
{
    public String Heading { set; get; }
}


public class NewsMap : EntityTypeConfiguration<News>
{
    public NewsMap()
    {
      //Base Object Common Mappings
      // How can we use a central mapping for all Base Abstract properties  


     }
 }
// Something like this but very open to any suggestion....
public class BosBaseEntityConfig<T> : EntityTypeConfiguration<T>
{
  public void BaseObjectMap( )
    { 
        // Primary Key
        this.HasKey(t => t.Id);

        // Properties
        this.Property(t => t.Id).HasDatabaseGeneratedOption(databaseGeneratedOption: DatabaseGeneratedOption.None);

        this.Property(t => t.RowVersion)
            .IsRequired()
            .IsFixedLength()
            .HasMaxLength(8)
            .IsRowVersion();

        //Column Mappings
        this.Property(t => t.Id).HasColumnName("Id");
    }
}

Answer 1

public class BaseEntityTypeConfiguration<T> : IEntityTypeConfiguration<T> where T : BaseEntity
{
    public virtual void Configure(EntityTypeBuilder<T> entity)
    {
        entity.HasKey(e => e.Id);
    }
}


public class NewsEntityTypeConfiguration : BaseEntityTypeConfiguration<News>
{
    public override void Configure(EntityTypeBuilder<News> entity)
    {
        base.Configure(entity);
        entity.ToTable("News");
    }
}

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.ApplyConfiguration(new NewsEntityTypeConfiguration());
}

Answer 2

Sorry I cannot comment but I would do as you are doing only swap these two lines around

      modelBuilder.Configurations.Add( conf );  // this has base mapping now
      var newsConf = new NewsConfiguration(conf); // now the Object specific properties stuff
   to
       new NewsConfiguration(conf); // now the Object 
       modelBuilder.Configurations.Add( conf );  // this has base mapping now

This helps EF with specialised fields.

Answer 3

The answer above definitely works, though this may be slight cleaner and has the advantage of working the same when registering the configurations in the DbContext.

public abstract class BaseEntity
{
    public int Id { get; set; }
}

public class Company : BaseEntity
{
    public string Name { get; set; }
}

internal class BaseEntityMap<T> : EntityTypeConfiguration<T> where T : BaseEntity
{
    public BaseEntityMap()
    {
        // Primary Key
        HasKey(t => t.Id);
    }
}

internal class CompanyMap : BaseEntityMap<Company>
{
    public CompanyMap()
    {
        // Properties
        Property(t => t.Name)
            .IsRequired()
            .HasMaxLength(256);
    }
}

public class AcmeContext : DbContext
{
    public DbSet<Company> Companies { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Configurations.Add(new CompanyMap());
    }
}

Above solution arrived at by Christian Williams and myself early one morning...

Answer 4

After 6 hrs I cracked it. I think it is a reasonably clean outcome. The trick is to forget doing every inside a class derived from EntityTypeConfiguration and build a custom BaseConfig and then to take this instance and add the specifics for this class. Hope it helps others doing code first with abstracts...

public  abstract class BosBaseObject
{
  public virtual Guid Id { set; get; }
  public virtual string ExternalKey { set; get; }
  public byte[] RowVersion { get; set; }
}
 public abstract class BosObjectDateManaged   :  BosBaseObject
{
    public DateTimeOffset ValidFrom { set; get; }
    public DateTimeOffset ValidTo { set; get; }
}
public class News : BosObjectDateManaged
{
    public String Heading { set; get; }
}



protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        var conf = new BosBaseEntityConfiguration<News>();//Construct config for Type
        modelBuilder.Configurations.Add( conf );  // this has base mapping now
        var newsConf = new NewsConfiguration(conf); // now the Object specific properties stuff

    }

}
public class BosBaseEntityConfiguration<T> : EntityTypeConfiguration<T> where T : BosBaseObject
{
   public BosBaseEntityConfiguration()
   {
       // Primary Key
       this.HasKey(t => t.Id);

       //// Properties
       this.Property(t => t.Id).HasDatabaseGeneratedOption(databaseGeneratedOption: DatabaseGeneratedOption.None);

       this.Property(t => t.RowVersion)
           .IsRequired()
           .IsFixedLength()
           .HasMaxLength(8)
           .IsRowVersion();

       //Column Mappings
       this.Property(t => t.Id).HasColumnName("Id");
   }
}
 public class NewsConfiguration  
{
    public  NewsConfiguration(BosBaseEntityConfiguration<News> entity)
    {
        // Table Specific & Column Mappings
        entity.ToTable("News2");
        entity.Property(t => t.Heading).HasColumnName("Heading2");
    }
}