CodeFirst EF Core - Implementing interfaces possible?

Question

I'm a little new to code-first in EF Core and I'm trying a few things out and I'm a little confused how to implement the below (or indeed whether it can be implemented or not).

In my model I have a class that maps entities to cases, with the following mapping class

public class CaseEntity
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int CaseEntityId { get; set; }
    
    public int CaseId { get; set; }
    public CaseModel Case { get; set; }
    public Guid EntityId { get; set; }
    public EntityModel Entity { get; set; }
}

I am now implementing the EntityModel object. However an entity can be either a Person or a Company. Both these have common properties, but there are some natural differences. What I wanted to do is create an IEntityModel interface and two classes as below

public class CaseEntity
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int CaseEntityId { get; set; }
    
    public int CaseId { get; set; }
    public CaseModel Case { get; set; }
    public Guid EntityId { get; set; }
    public IEntityModel Entity { get; set; }
}

public interface IEntityModel
{
    Guid EntityId { get; set; }
    PostalAddress PrincipalAddress { get; set; }
}

public class CompanyEntity : IEntityModel
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Guid EntityId { get; set; }
    public string CompanyName { get; set; }
    public PostalAddress PrincipalAddress { get; set; }
}

public class PersonEntity : IEntityModel
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Guid EntityId { get; set; }
    public PostalAddress PrincipalAddress { get; set; }
    public string FirstNames { get; set; }
    public string Surname { get; set; }
}

When I try to build this I get the error

The property 'CaseEntity.Entity' is of an interface type ('IEntityModel'). If it is a navigation, manually configure the relationship for this property by casting it to a mapped entity type.

Otherwise, ignore the property using the [NotMapped] attribute or 'EntityTypeBuilder.Ignore' in 'OnModelCreating'.

I'm not 100% certain I can do what I'm trying to do. Searching around has left me a little confused (is that a solution to implement kind of functionality like, or should I use implement an entity class that has all the properties need to support a Company or a Person?)

Serge · Accepted Answer · 2021-08-28 15:17:58Z

1

I think it would be better if you create a base class

public class EntityModel:IEntityModel
{
   [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
   public  int EntityId { get; set; }
   publlic  PostalAddress PrincipalAddress { get; set; }
}

CompanyEntity

public class CompanyEntity : EntityModel
{
    public string CompanyName { get; set; }
}

CaseEntity

public class CaseEntity
    
    {
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int CaseEntityId { get; set; }
    
    
    public int CaseId { get; set; }
    public CaseModel Case { get; set; }

    public int EntityId { get; set; }
    public virtual EntityModel EntityModel { get; set; }
    }

answered Aug 28, 2021 at 15:17

Serge

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2 Comments

Ian Boggs Over a year ago

This doesn't seem to create the CompanyEntity object in the database when it builds the database

Ian Boggs Over a year ago

Actually it is working now, I'd missed off some of the linking properties. It does make a bit of a mess of the Entities table in the database, as it adds all the properties from Company and Person models to the one table, with a Discriminator column, but I think I can work with that.

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