Projections: Interface, DTO, Dynamic

JPA projections fetch only the columns your API needs – interface-based uses a proxy with getter methods, DTO-based uses a constructor expression (fastest), and dynamic lets the caller choose the projection at runtime.

Interface projections support SpEL @Value for computed fields and nested interfaces for associations; DTO projections are the fastest with no proxy overhead; dynamic projections let the caller choose the shape at runtime.

Projections fetch only the columns you need as lightweight read models, far cheaper than loading full entities.

Interface projection is a proxy over selected getters, DTO/class projection is a constructor expression or record (fastest), and dynamic projection takes a Class<T> so the caller chooses the shape at runtime.