如何通过 OnModelCreating 方法动态创建外键

Question

On my EF6 model I have created certain base classes that contain properties/columns that I want to be inherited across several entities.

Here is a simple example of the concept:

public class Replaceable 
{
    [Column("REPLACING")]
    public int Replacing { get; set; }
}

[Table("PARTS")]
public class Part : Replaceable
{
    [Column("ID"), Key]
    public int Id { get; set; }

    [Column("PART_NUMBER")]
    public string PartNumber { get; set; }
}

So the REPLACING property & column will be inherited to Part-class/PARTS-table.

The REPLACING column is supposed to point towards an ID in the same table. For example if you replace a part you want to keep track of what replaced what.

What I want to do (if possible) through OnModelCreating is:

• Get all entities that inherit from Replaceable.
• Mark the column REPLACING as a foreign key and point it to the entity's Primary Key (PART_ID, COMPONENT_ID etc).

The trick here is how to get the name of the ID column of each entity's table since all of them are not called ID but PART_ID, COMPONENT_ID etc.

Is this even possible? An alternative practice is also welcome.

Answer 1

You can use a base configuration class:

public abstract class ReplaceableConfiguration<T> : EntityTypeConfiguration<T>
    where T : Replaceable
{
    public ReplaceableConfiguration()
    {
        this.Property(r => r.Replacing).HasColumnName(typeof(T).Name + "_ID");
    }
}

And derive as many concrete classes as you want.

public class PartConfiguration : ReplaceableConfiguration<Part>
{ }

public class ComponentConfiguration : ReplaceableConfiguration<Component>
{ }

I tried this with just two classes:

modelBuilder.Configurations.Add(new PartConfiguration());
modelBuilder.Configurations.Add(new ComponentConfiguration());

Which gave me this DDL:

CREATE TABLE [dbo].[PARTS] (
    [ID] [int] NOT NULL IDENTITY,
    [PART_NUMBER] [nvarchar](max),
    [Part_ID] [int] NOT NULL,
    CONSTRAINT [PK_dbo.PARTS] PRIMARY KEY ([ID])
)

CREATE TABLE [dbo].[COMPONENTS] (
    [ID] [int] NOT NULL IDENTITY,
    [COMPONENT_NUMBER] [nvarchar](max),
    [Component_ID] [int] NOT NULL,
    CONSTRAINT [PK_dbo.COMPONENTS] PRIMARY KEY ([ID])
)