如何使用实体框架将属性映射到不同的表

Question

My database looks something like the following:

dbo.Products Table:

Id        | int
Status    | tinyint

dbo.ProductNames Table:

ProductId | int
Name      | nvarchar(4000)

And a simplifed version of the code would be:

public class Product{
    public int Id { get; set; }
    public string Name { get; set; }
    public ObjectStatus Status { get; set; }
}

public class ProductEntityConfiguration : EntityConfiguration<Product> {
    public ProductEntityConfiguration() {
        ToTable("Products");
        HasKey(p => p.Id);
        Property(p => p.Id).HasColumnName("Id");
        Property(p => p.Status).HasColumnName("Status");
    }
}

How can I map the product name, which exists in a different table as a normal property, so that if someone requests it, EF must join the two tables by the Id?

Answer 1

I think you have to use entity splitting in this case. You have one entity (Product) and you want to split it into two tables (Products and ProductNames). Try to use the following mapping:

  public class ProductEntityConfiguration : EntityConfiguration<Product> 
  {
      public ProductEntityConfiguration() 
      {
         Map(m => 
         { 
            m.Property(t => t.ProductId).HasColumnName("MyIdChanged");
            m.Property(t => t.Status).HasColumnName("Status");                
            m.ToTable("Product")
         }) 
         .Map(m => 
         { 
            m.Property(t => t.ProductId).HasColumnName("MyProductIdChanged");
            m.Property(t => t.Name).HasColumnName("MyProductName");
            m.ToTable("ProductNames"); 
         });
      }
  }

This will configure the appropriate primary keys and foreign keys and do the joins automatically.

Answer 2

I know this is super late, but I was researching the same issue and I find the accepted answer is a little too complicated to my liking (I need to join 3 tables), and I prefer my code to be simpler.

So I chose to use [NotMapped] property instead, which makes the code simpler.

Here is a sample solution based on the question above.

public class Product{
    public int Id { get; set; }    
    public ObjectStatus Status { get; set; }

    // Foreign keys
    public int ProductNameId { get; set; }
    public virtual ProductName ProductName { get; set; }

    [NotMapped]
    public string Name => ProductName?.Name;    
}

public class ProductEntityConfiguration : EntityConfiguration<Product> {
    public ProductEntityConfiguration() {
        ToTable("Products");
        HasKey(p => p.Id);
        Property(p => p.Id).HasColumnName("Id");
        Property(p => p.Status).HasColumnName("Status");

        Property(p => p.ProductNameId).HasColumnName(@"ProductNameId").HasColumnType("int").IsRequired();
        HasRequired(a => a.ProductName).WithMany(b => b.Products).HasForeignKey(c => c.ProductNameId);
    }
}

This solution may 'look' complicated than the accepted answer because I am adding a foreign key here. But I bet most people already have these foreign keys anyway, so all you need to do is add the NotMapped property and you are done. It would be just a 1 line change.