POCO vs. DTO: When Should You Use Plain Old CLR Objects Instead of Data Transfer Objects?

POCO vs. DTO: Distinguish between plain old CLR objects and data transfer objects

In software development, the terms "POCO" and "DTO" are often used interchangeably, but they represent different concepts.

Plain Old CLR Object (POCO)

POCO follows the principles of object-oriented programming and has both state (properties) and behavior (methods). The emergence of POCO is a response to the complexity of Enterprise JavaBeans (EJB), which emphasizes the use of simple, lightweight objects.

Data Transfer Object (DTO)

Unlike POCO, the sole purpose of DTO is to transfer data between different layers of the application. They have no behavior and are designed to be lightweight and easily serializable.

Key differences

The key difference between POCOs and DTOs is their intended role:

• POCO: Represents an object-oriented programming approach that focuses on domain modeling and business logic.
• DTO: Implements a pattern for efficient data transfer between layers.

The pitfall of treating POCO as a DTO

While it may be tempting to use POCOs as DTOs, this results in an anemic domain model that lacks the richness and complexity required for effective business logic. Furthermore, DTOs should prioritize data transfer capabilities rather than representing the true structure of the domain, leading to potential structural mismatches.

Best Practices

In complex fields, it is recommended to separate the field POCO from the DTO. This approach adheres to domain-driven design principles and uses an anti-corrosion layer to cleanly isolate these two types of objects. By maintaining this distinction, developers can take advantage of POCOs and DTOs while ensuring the integrity of their domain model.

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