C# : Domain Objects, Entities, DTOs, and Models - Same same but different

 

In C# development, we often encounter various types of classes that represent different concepts within our applications. Understanding the distinctions between domain objects, entities, DTOs (Data Transfer Objects), and models is crucial for designing robust and maintainable systems. In this blog post, we'll delve into each of these concepts, explore their roles, and provide practical examples in C# to illustrate their usage.

1. Domain Objects:

Definition: Domain objects represent real-world entities or concepts within the problem domain of an application. They encapsulate business logic and behaviors related to specific aspects of the domain.

Example:

public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
    public decimal Price { get; set; }

    public bool IsInStock()
    {
        // Business logic to determine if the product is in stock
    }
}

2. Entities:

Definition: Entities are objects that have a distinct identity and lifecycle within an application. They are typically persisted to a database and represent the core data structures of the application.

Example:

public class Customer
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Email { get; set; }
    // Other properties and methods
}

3. DTOs (Data Transfer Objects):

Definition: DTOs are lightweight objects used to transfer data between different layers of an application, such as between the presentation layer and the business logic layer. They often mirror the structure of domain objects or entities but may contain only the necessary data for a specific operation.

Example:

public class OrderDto
{
    public int OrderId { get; set; }
    public DateTime OrderDate { get; set; }
    public decimal TotalAmount { get; set; }
    // Other properties as needed
}

4. Models:

Definition: Models are objects that represent the structure and state of data within an application. They may include a combination of domain objects, entities, DTOs, or other data structures.

Example:

public class ProductViewModel
{
    public int Id { get; set; }
    public string Name { get; set; }
    public decimal Price { get; set; }
    // Other properties as needed
}

Real-time Order Processing Example: Understanding Use Cases

Let's consider a real-world scenario of an e-commerce platform processing orders in real-time. We'll examine different aspects of the order processing workflow and categorize them according to domain objects, entities, DTOs (Data Transfer Objects), and models.

1. Domain Objects:

Domain objects represent key entities or concepts within the e-commerce domain, encapsulating business logic and behaviors.

• Product: Represents individual products available for purchase, including properties such as name, price, and availability.
• Order: Represents a customer's order, containing details such as order ID, customer information, and order items.
• Customer: Represents a registered customer, including properties like name, email, and shipping address.

2. Entities:

Entities are objects that have a distinct identity and are persisted to a database.

• OrderEntity: Represents the order data stored in the database, mapping to the order table and containing properties like order ID, customer ID, and order status.
• ProductEntity: Represents the product data stored in the database, mapping to the product table and containing properties like product ID, name, and price.
• CustomerEntity: Represents the customer data stored in the database, mapping to the customer table and containing properties like customer ID, name, and email.

3. DTOs (Data Transfer Objects):

DTOs are lightweight objects used for transferring data between different layers of the application.

• OrderDto: Contains a subset of order data used for transferring order information between the presentation layer and the business logic layer. It may include properties like order ID, customer name, and total amount.
• ProductDto: Contains product data used for transferring product information between layers, including properties like product ID, name, and price.
• CustomerDto: Contains customer data used for transferring customer information between layers, including properties like customer ID, name, and email.

4. Models:

Models represent the structure and state of data within the application, combining domain objects, entities, DTOs, or other data structures.

• OrderViewModel: Represents the order data used for presentation purposes, containing properties like order ID, customer name, order date, and order status.
• ProductViewModel: Represents product data used for presentation, including properties like product ID, name, price, and availability.
• CustomerViewModel: Represents customer data used for presentation, containing properties like customer ID, name, email, and shipping address.

Conclusion:

Understanding the distinctions between domain objects, entities, DTOs, and models is essential for designing well-structured and maintainable C# applications. Each type serves a specific purpose within the application architecture, whether it's encapsulating business logic, representing database entities, transferring data between layers, or modeling data for presentation. By using these concepts appropriately, developers can create robust and scalable applications that meet the requirements of their domain.