Best practices for using DTOs (Data Transfer Objects) in a clean architecture

What are DTOs and why use them?

Data Transfer Objects (DTOs) are objects that transport data between processes. They are often used in applications to transfer data between the presentation layer and the service layer or between microservices. The use of DTOs is a common practice in clean architectures as it allows for the separation of concerns, ensuring that parts of the application are not tightly coupled with one another. Additionally, DTOs help simplify communication between different parts of a system, making it more flexible and easier to maintain.

Advantages of DTOs in a Clean Architecture

DTOs offer a number of advantages in a clean architecture, which can be crucial for improving the efficiency and maintainability of your code:

• Reduced Coupling: By using DTOs, the presentation layer does not need to know the structure of the domain entities, which reduces coupling and makes the application more flexible to changes.
• Data Validation: DTOs can be used to validate data before it is sent to the service layer, ensuring that only valid data is processed. This helps avoid errors and inconsistencies in the data.
• Ease of Serialization: DTOs are structured in a way that facilitates serialization and deserialization, especially when interacting with APIs, where communication between systems may require specific formats such as JSON or XML (WARREN and WAGNER, 2024).
• Performance: In some situations, using DTOs can improve application performance by transferring only the necessary data and avoiding the sending of unnecessary information.
• Documentation: DTOs can serve as a form of API documentation, as they clearly define what data is expected and returned, facilitating integration with other systems.

Best Practices for Creating DTOs

The creation of DTOs should follow some best practices to ensure the efficiency and maintainability of the code. The main practices include:

• Clear Naming: DTO names should be self-explanatory, clearly reflecting the purpose of the object. For example, a DTO for a user can be called UserDTO, while a DTO for a transaction can be called TransactionDTO.
• Immutable Properties: Whenever possible, use immutable properties to ensure that data is not accidentally changed after being created. This increases the security and predictability of the code.
• Avoid Business Logic: DTOs should be simple and not contain business logic. They should be used only for data transport, keeping the responsibility of business logic in service or domain classes.
• Limit Responsibility: Each DTO should have a clear purpose and not be a "catch-all" for data. This helps maintain cohesion and facilitates maintenance.
• Documentation and Annotations: Use comments and annotations to document the properties of the DTO, facilitating understanding and maintenance by other developers.

Example of DTO in C#

Below is a simple example of a DTO in C# for a user registration scenario:

public class UserDTO
{
    public readonly string FirstName;
    public readonly string LastName;
    public readonly string Email;
    
    public UserDTO(string firstName, string lastName, string email)
    {
        FirstName = firstName;
        LastName = lastName;
        Email = email;
    }
}
    

Mapping Between Entities and DTOs

An important aspect when working with DTOs is the mapping between domain entities and DTOs. This can be done manually or using libraries like AutoMapper (BOGARD, 2024). Here is an example of manual mapping:

public class User
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Email { get; set; }
    public UserDTO MapToDTO()
    {
        return new UserDTO(this.FirstName, this.LastName, this.Email);
    }
}
    

Using AutoMapper for DTO Mapping

The AutoMapper library can simplify the mapping process between entities and DTOs. Here’s how to configure it:

var config = new MapperConfiguration(cfg => {
    cfg.CreateMap();
});

IMapper mapper = config.CreateMapper();
User user = new User { FirstName = "John", LastName = "Doe", Email = "john@example.com" };
UserDTO userDTO = mapper.Map(user);
    

DTOs and Data Validation

DTOs can also be used for data validation. You can use data annotation attributes to validate the properties of a DTO. Here’s an example:

using System.ComponentModel.DataAnnotations;

public class UserDTO
{
    [Required]
    public string FirstName { get; set; }
    
    [Required]
    public string LastName { get; set; }
    
    [EmailAddress]
    public string Email { get; set; }
}
    

When to Use DTOs

Although DTOs are extremely useful, it is important to know when to use them. They are most appropriate in the following situations:

• The presentation layer needs a data structure different from the domain entity, thereby allowing for greater decoupling between parts of the system.
• You are dealing with operations where the amount of data transferred needs to be reduced, such as API calls that require efficiency in bandwidth usage.
• You want to add a layer of validation between user input and business logic, ensuring that only valid data is processed.
• When integrating different systems, where data structures may vary, DTOs help standardize communication between them.

Potential Disadvantages of DTOs

Despite the advantages, the use of DTOs can also present disadvantages, such as:

• Additional Complexity: The introduction of DTOs can increase code complexity, especially if not managed properly. Creating multiple DTOs can lead to an increase in the number of classes and difficulty in navigating the code.
• Maintenance: Maintaining multiple classes (entities and DTOs) can be a challenge, especially in large applications. It is important to have a clear process for updating both entities and DTOs when needs change.
• Mapping Overhead: The mapping between entities and DTOs can introduce overhead, especially if done manually, which can impact application performance if not optimized.

Conclusion

The use of DTOs in a clean architecture is a recommended practice that can improve the organization and maintainability of the code. By following the best practices mentioned above, you can ensure that your DTOs are efficient and easy to use. Always remember to assess the need for DTOs in your project, balancing their advantages and disadvantages to achieve a robust and scalable architecture. The adoption of DTOs should be a conscious decision, considering the context and specific needs of your system.