SOLID & Design Patterns Interview Question #114

What is the Mapper pattern and when is mapping useful?

Architectural Patterns, Application Boundaries & Distributed Design Patterns Senior Advanced

Quick Interview Answer

Mapping translates data between models that serve different responsibilities, such as API DTOs, application models, domain objects, and persistence representations. It prevents those boundaries from becoming the same model accidentally.

Detailed Explanation

Mapping can be manual or automated. Manual mapping is often clearer for important domain transitions, while mapping libraries can reduce repetitive property-copying when mappings remain simple and explicit.

Code Example

public static OrderDto ToDto(Order order)
{
    return new OrderDto(
        order.Id,
        order.Customer.Name,
        order.Total.Amount,
        order.Status.ToString());
}