Table Splitting

Your Customer entity has 47 properties. Most queries only need the basic information: name, email, and contact details. But every time you load a customer, EF Core pulls all 47 columns from the database, including the large ProfileData JSON blob that’s rarely used.

This is where table splitting can help: split your large entity into multiple classes that map to the same table, loading only what you need when you need it.

But table splitting is a double-edged sword. Use it wrong, and you’ll make performance worse, not better.

Understanding Table Splitting

Table splitting maps multiple entity classes to the same database table:

// Single table with many columns
CREATE TABLE Customers (
    Id int PRIMARY KEY,
    Name nvarchar(100),
    Email nvarchar(200),
    Phone nvarchar(20),
    -- Frequently accessed columns above
    
    ProfileData nvarchar(max),
    Preferences nvarchar(max), 
    MarketingMetadata nvarchar(max),
    LastLoginDetails nvarchar(max),
    -- Rarely accessed columns below
    CreatedAt datetime2,
    ModifiedAt datetime2
);

Instead of one large entity, you create multiple focused entities:

// Frequently accessed data
public class Customer
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Email { get; set; }
    public string Phone { get; set; }
    
    // Navigation to extended data
    public CustomerExtended Extended { get; set; }
}

// Infrequently accessed data
public class CustomerExtended
{ …