# A Note on Data Transfer Objects (DTO)s

Data Transfer Objects (DTOs) are introduced to decouple (JPA) entities from the UI
    DTOs are also motivated by their typesafe nature
    Lacking typesafety, JSON-P JsonObjects are not used as DTOs
    Most DTOs are exposed as HTTP/JSON
    Often 3rd party libraries are used to map a DTO into a JSON
    Sometimes DTOs are called Value Objects
    The vast majority of DTOs remains identical to entities over the entire lifecycle of a project
    Copying data between DTOs and entities requires series of getter-setter invocations
    DTOs are growing, the mapping logic is extracted into dedicated "mappers"
    DTOs and mappers introduce a significant amount of untested code, which disturbs the code coverage statistics
    Getters and setters, constructor tests are written to increase the code coverage
    Now: structural JPA entity code changes, affect DTOs, mappers and the corresponding unit tests


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