Entity Framework Core 2 – Table splitting

Entity Framework Core 2 was released on August 14th. It brought new features.

On this article I will explain one of them : Table splitting

Table carving looks like owned types, but it’s not the same thing.
But an SQL table can be projected in several entities (and not a simple class like the possessed types).
Each entity must have the same primary key, and each entity must be configured and configured separately.

Example:

We will project this table in 2 entities, Product and ProductDetails:

public class Product
{
   public int ProductID { get; set; }
   public string Name { get; set; }
   public decimal Cost { get; set; }

   public ProductDetail Details { get; set; }
}

public class ProductDetail
{
   public int ProductID { get; set; }
   public decimal ListPrice { get; set; }
   public string Size { get; set; }
   public decimal? Weight { get; set; }

   public Product Product { get; set; }
}

Then let’s configure these 2 entities

• A navigation property from Product to ProductDetails
• A navigation property from ProductDetails to Product

It will we configured as a one to one relationship :

public class ProductConfiguration : IEntityTypeConfiguration<Product>
{
   public void Configure(EntityTypeBuilder<Product> builder)
   {
      builder.HasKey(x => x.ProductID);
      builder.HasOne(e => e.Details).WithOne( o=> o.Product).HasForeignKey<ProductDetail>(e => e.ProductID);
      builder.ToTable("Product");
   }
}

public class ProductDetailConfiguration : IEntityTypeConfiguration<ProductDetail>
{
   public void Configure(EntityTypeBuilder<ProductDetail> builder)
   {
      builder.HasKey(x=> x.ProductID);
      builder.HasOne(e => e.Product).WithOne(o => o.Details).HasForeignKey<Product>(e => e.ProductID);
      builder.ToTable("Product");
   }
}

It’s identical to two sql tables linked by a one to one relationship.

If you want to get ProductDetails when you quert a Product you must add .Include(“ProductDetails”) extension method to the query, like two sql tables linked by a one to one relationship as well.

Example:

public List<Product> GetProductsWithDetails()
{
   var query = _context.Products.Include(p=> p.Details).ToList();
}

This feature would be commonly used to get from database data you only want to query, it avoids developers to make multiple versions of a same entity, each one used depending the data you want, especially for performance reasons.

So it’s a great feature ?I love it! 🙂