Table-per-type inheritance uses a separate table in the database to maintain data for non-inherited properties and key properties for each type in the inheritance hierarchy.
Table per Type is about representing inheritance relationships as relational foreign key associations.
Every class and subclass including abstract classes has its own table.
The table for subclasses contains columns only for each non-inherited property along with a primary key that is also a foreign key of the base class table.
By default, EF Core maps an inheritance hierarchy of .NET types to a single database table. This is known as table-per-hierarchy (TPH) mapping. EF Core 5.0 also allows mapping each .NET type in an inheritance hierarchy to a different database table; known as table-per-type (TPT) mapping.
Let's consider the following simple model with a mapped hierarchy.
public class Person
{
public int Id { get; set; }
public string FullName { get; set; }
}
public class Student : Person
{
public DateTime EnrollmentDate { get; set; }
}
public class Teacher : Person
{
public DateTime HireDate { get; set; }
}
Here is the context class implementation without any additional configuration.
public class EntityContext : DbContext
{
protected override void OnConfiguring(DbContextOptionsBuilder opBuilder)
{
opBuilder.UseSqlServer("Data Source=(localdb)\\ProjectsV13;Initial Catalog=PeopleContextDb;");
}
public DbSet<Person> People { get; set; }
public DbSet<Student> Students { get; set; }
public DbSet<Teacher> Teachers { get; set; }
}
By default, EF Core will map this to a single table.
In the TPT mapping pattern, all the types are mapped to individual tables. Properties that belong solely to a base type or derived type are stored in a table that maps to that type.
Entity types can be mapped to different tables using mapping attributes.
[Table("People")]
public class Person
{
public int Id { get; set; }
public string FullName { get; set; }
}
[Table("Students")]
public class Student : Person
{
public DateTime EnrollmentDate { get; set; }
}
[Table("Teachers")]
public class Teacher : Person
{
public DateTime HireDate { get; set; }
}
However, mapping each entity type to a different table will instead result in one table per type.
