Advertisement
Поиск  
Always will be ready notify the world about expectations as easy as possible: job change page
Mar 1, 2023

Inheritance strategies in Entity Framework Core 7

Автор:
Alper Ebiçoğlu
Источник:
Просмотров:
1797

In this article, I’ll show you all the object mapping strategies of EF Core and especially the new one: TPC Inheritance Mapping. TPC mapping is the new feature introduced with Entity Framework Core 7. It’s called Table Per Concrete type inheritance mapping. I’ll explain the EF Core’s inheritance mapping strategies with how the inherited entity and the specific information are saved into a relational database. I’ll also explain which strategy is best for your case.

By default, EF Core maps an inheritance hierarchy of .NET types to a single database table. And it’s called TPH (table-per-hierarchy) mapping.

In the previous versions EF Core , Table Per Hierarchy (TPH) or Table Per Type (TPT) were supported. And now TPC came!

To explain in a more clear way, I’ll use the following entity model. Car, Bus and Motorcylce are inherited from the Vehicle object.

public abstract class Vehicle
{
    public int Id { get; set; }
    public string VehicleModel { get; set; }
}

//////////////////////////////////////

public class Car : Vehicle
{
    public string Segment { get; set; }
}

//////////////////////////////////////

public class Bus : Vehicle
{
    public int? SeatCount { get; set; }
}

//////////////////////////////////////

public class Motorcycle : Vehicle
{
    public int CylinderCount { get; set; }
}

Here’s the list of available strategies to map Car, Bus and Motorcycle.

TPH (Table Per Hierarchy)

TPH maps an inheritance hierarchy of .NET types to a single database table. So a single table is created for all types. This is the default behavior of EF Core. If you explicitly want to use this strategy, you can write UseTphMappingStrategy() to the root entity in the OnModelCreating() method in the DbContext class. As you see from the following table, it adds an extra column, Discriminator to separate the Car, Bus and Motorcycle. This way of persistence is an unnormalized form.

CREATE TABLE [Vehicles] (
    [Id] int NOT NULL IDENTITY,   
    [Discriminator] nvarchar(max) NOT NULL,  -- "Car", "Bus", "Motorcylce"
    [VehicleModel] nvarchar(max) NOT NULL,
    [Segment] nvarchar(max) NULL,
    [SeatCount] int NULL,
    [CylinderCount] int NOT NULL
);

TPT (Table per Type)

With the TPT strategy, a different table is created for every type. The table itself is used to determine the type of the object saved, and each table contains only columns for the properties of that type. The data is saved in multiple tables, and this way of persistence is normalized form.

CREATE TABLE [Vehicles] (
    [Id] int NOT NULL IDENTITY,
    [VehicleModel] nvarchar(max) NOT NULL
);

CREATE TABLE [Car] (
    [Id] int NOT NULL,
    [Segment] nvarchar(max) NULL
);

CREATE TABLE [Bus] (
    [Id] int NOT NULL,
    [SeatCount] int NULL,
);

CREATE TABLE [Motorcycle] (
    [Id] int NOT NULL,
    [CylinderCount] int NOT NULL
);

If you explicitly want to use this strategy, you can write UseTptMappingStrategy() to the root entity in the OnModelCreating() method in the DbContext class.

TPC (Table Per Concrete type)

It’s the new strategy that has been introduced with EF Core 7. In this way, a different table is created for each concrete type. While in the TPT, the table itself indicates the type of the object saved, in TPC, each table contains columns for every property in the concrete type and its base types. As you see from the following tables, no Vehicles table is being created. The VehicleModel field is common in each table.

CREATE TABLE [Car] (
    [Id] int NOT NULL DEFAULT (NEXT VALUE FOR [VehicleIds]),
    [VehicleModel] nvarchar(max) NOT NULL, -- common field for each type
    [Segment] nvarchar(max) NULL
);

CREATE TABLE [Bus] (
    [Id] int NOT NULL DEFAULT (NEXT VALUE FOR [VehicleIds]),
    [VehicleModel] nvarchar(max) NOT NULL, -- common field for each type
    [SeatCount] int NULL
);

CREATE TABLE [Motorcycle] (
    [Id] int NOT NULL DEFAULT (NEXT VALUE FOR [VehicleIds]),
    [VehicleModel] nvarchar(max) NOT NULL, -- common field for each type
    [CylinderCount] int NOT NULL
);

This strategy maps each .NET type to a different database table. You write UseTpcMappingStrategy() to the root entity in the root entity in the OnModelCreating() method in the DbContext class.

How do you choose which mapping type is best for you?

  • TPH: In most cases, the TPH mapping is a good choice which is the default one. This way, the table columns increase because all the properties are saved in the same table, but it’s easy to query in a single table.
  • TPT In this form, data is persisted in a normalized form. For this reason, you can choose TPT, but generally, it’s not being used. But the disadvantage is when you filter by VehicleModel column, it must join Vehicles, Bus, Car, Motorcycle tables. So it's not a feasible fetching way.
  • TPC: This new strategy is similar to TPT but resolves some of the TPT problems. Because it stores the data in its own table, it doesn’t divide across multiple tables. This option can be chosen when the mapped hierarchy is large and has many concrete types, each with many properties.

For example, if Car, Bus, or Motorcycle have 20 properties for each type, then it's better to store them in a separate table, so we should use TPC. But if these entities have only 3-5 properties, then TPH is the way to go.

Похожее
Mar 15, 2023
Author: Alex Maher
1. JustDecompileJustDecompile is a free decompiler tool that allows you to easily decompile .NET assemblies into readable code. With this tool, you can quickly and easily analyze the code of any .NET application, even if you don’t have the original...
May 13, 2023
Author: Juan Alberto España Garcia
Introduction to Async and Await in C#Asynchronous programming has come a long way in C#. Prior to the introduction of async and await, developers had to rely on callbacks, events and other techniques like the BeginXXX/EndXXX pattern or BackgroundWorker.These methods...
Jul 10, 2021
Author: Sam Walpole
I've recently gotten into using Docker in my development cycle and I'm really enjoying how much of a wonderful tool it is. One thing that always used to be a pain was setting up a development server to run SQL...
Dec 20, 2023
Author: Fiodar Sazanavets
You can run a single monolithic instance of a server application only if the number of clients accessing your application doesn’t exceed a couple of thousand. But what if you expect hundreds of thousands, or even millions, of clients to...
Написать сообщение
Почта
Имя
*Сообщение


© 1999–2024 WebDynamics
1980–... Sergey Drozdov
Area of interests: .NET Framework | .NET Core | C# | ASP.NET | Windows Forms | WPF | HTML5 | CSS3 | jQuery | AJAX | Angular | React | MS SQL Server | Transact-SQL | ADO.NET | Entity Framework | IIS | OOP | OOA | OOD | WCF | WPF | MSMQ | MVC | MVP | MVVM | Design Patterns | Enterprise Architecture | Scrum | Kanban