What is a Data Transfer Object DTO

Question

What is a Data Transfer Object   In MVC are the model classes DTO  and if not what are the differences and do we need both

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Data transfer object  DTO  describes    an object that carries data between processes     Wikipedia  or an    object that is used to encapsulate data  and send it from one subsystem of an application to another     Stack Overflow answer

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A DTO is a dumb object - it just holds properties and has getters and setters  but no other logic of any significance  other than maybe a compare   or equals   implementation   Typically model classes in MVC  assuming  net MVC here  are DTOs  or collections aggregates of DTOs

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The principle behind Data Transfer Object is to create new Data Objects that only include the necessary properties you need for a specific data transaction  Benefits include  Make data transfer more secure Reduce transfer size if you remove all unnecessary data  Read More  https   www codenerd co za what-is-data-transfer-objects

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The definition for DTO can be found on Martin Fowler s site   DTOs are used to transfer parameters to methods and as return types   A lot of people use those in the UI  but others inflate domain objects from them

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In general Value Objects should be Immutable  Like Integer or String objects in Java  We can use them for transferring data between software layers  If the software layers or services running in different remote nodes like in a microservices environment or in a legacy Java Enterprise App  We must make almost exact copies of two classes  This is the where we met DTOs    -----------                                                     --------------    SERVICE 1  -- gt  Credentials DTO  gt -------- gt  Credentials DTO  gt --   AUTH SERVICE    -----------                                                     --------------    In legacy Java Enterprise Systems DTOs can have various EJB stuff in it   I do not know this is a best practice or not but I personally use Value Objects in my Spring MVC Boot Projects like this            ------------           ------------------                               ------------  - gt  Form                - gt  Form                      - gt  Entity                                            Controller             Service   Facade                                 Repository    lt - View                 lt - View                       lt - Entity   Projection View                         ------------           ------------------                               ------------    Controller layer doesn t know what are the entities are  It communicates with Form and View Value Objects  Form Objects has JSR 303 Validation annotations  for instance  NotNull  and View Value Objects have Jackson Annotations for custom serialization   for instance  JsonIgnore   Service layer communicates with repository layer via using Entity Objects  Entity objects have JPA Hibernate Spring Data annotations on it  Every layer communicates with only the lower layer  The inter-layer communication is prohibited because of circular cyclic dependency   User Service ---- gt  XX CANNOT CALL XX ---- gt  Order Service   Some ORM Frameworks have the ability of projection via using additional interfaces or classes  So repositories can return View objects directly  There for you do not need an additional transformation   For instance this is our User entity    Entity public final class User       private String id      private String firstname      private String lastname      private String phone      private String fax      private String address         Accessors         But you should return a Paginated list of users that just include id  firstname  lastname  Then you can create a View Value Object for ORM projection   public final class UserListItemView       private String id      private String firstname      private String lastname         Accessors         You can easily get the paginated result from repository layer  Thanks to spring you can also use just interfaces for projections   List lt UserListItemView gt  find Pageable pageable     Don t worry for other conversion operations BeanUtils copy method works just fine

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To me the best answer to the question what is a DTO is that DTO s are simple objects that should not contain any business logic or methods implementation that would require testing  Normally your model  using the MVC pattern  are intelligent models  and they can contain a lot of some  methods that do some different operations for that model specifically  not business logic  this should be at the controllers   However  when you transfer data  eg  calling a REST  GET POST whatever  endpoint from somewhere  or consuming a webservice using SOA  etc     you do not want to transmit the big sized object with code that is not necessary for the endpoint  will consume data  and slow down the transfer

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DefN  A DTO is a hardcoded data model  It only solves the problem of modeling a data record handled by a hardcoded production process  where all fields are known at compile-time and therefore accessed via strongly typed properties   In contrast  a dynamic model or  property bag  solves the problem of modeling a data record when the production process is created at runtime   The Cvar  A DTO can be modeled with fields or properties  but someone invented a very useful data container called the Cvar  It is a reference to a value  When a DTO is modeled with what I call reference properties  modules can be configured to share heap memory and thereby collaboratively work on it  This completely eliminates parameter passing and O2O communication from your code  In other words  DTOs having reference properties allow code to achieve zero coupling       class Cvar              class Cvar lt T gt    Cvar               public T Value   get  set               class MyDTO               public Cvar lt int gt  X   get  set            public Cvar lt int gt  Y   get  set            public Cvar lt string gt  mutableString   get  set        gt            Source   http   www powersemantics com   Dynamic DTOs are a necessary component for dynamic software  To instantiate a dynamic process  one compiler step is to bind each machine in the script to the reference properties the script defines  A dynamic DTO is built by adding the Cvars to a collection          a dynamic DTO     class CvarRegistry   Dictionary lt string  Cvar gt        Contentions  Note   because Wix labeled the use of DTOs for organizing parameters as an  anti-pattern   I will give an authoritative opinion       return View model       MVC disagrees   My collaborative architecture replaces design patterns  Refer to my web articles   Parameters provide immediate control of a stack frame machine  If you use continuous control and therefore do not need immediate control  your modules do not need parameters  My architecture has none  In-process configuration of machines  methods  adds complexity but also value  performance  when the parameters are value types  However  reference type parameters make the consumer cause cache misses to get the values off the heap anyway -- therefore  just configure the consumer with reference properties  Fact from mechanical engineering   reliance on parameters is a kind of preoptimization  because processing  making components  itself is waste  Refer to my W article for more information  http   www powersemantics com w html   Fowler and company might realize the benefits of DTOs outside of distributed architecture if they had ever known any other architecture  Programmers only know distributed systems  Integrated collaborative systems  aka production aka manufacturing  are something I had to claim as my own architecture  because I am the first to write code this way   Some consider the DTO an anemic domain model  meaning it lacks functionality  but this assumes an object must own the data it interacts with  This conceptual model then forces you to deliver the data between objects  which is the model for distributed processing  However on a manufacturing line  each step can access the end product and change it without owning or controlling it  That s the difference between distributed and integrated processing  Manufacturing separates the product from operations and logistics   There s nothing inherently wrong with modeling processing as a bunch of useless office workers who e-mail work to one another without keeping an e-mail trail  except for all the extra work and headache it creates in handling logistics and return problems  A properly modeled distributed process attaches a document  active routing  to the product describing what operations it came from and will go to  The active routing is a copy of the process source routing  which is written before the process begins  In the event of a defect or other emergency change  the active routing is modified to include the operation steps it will be sent to  This then accounts for all the labor which went into production

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A Data Transfer Object is an object that is used to encapsulate data  and send it from one subsystem of an application to another   DTOs are most commonly used by the Services layer in an N-Tier application to transfer data between itself and the UI layer  The main benefit here is that it reduces the amount of data that needs to be sent across the wire in distributed applications  They also make great models in the MVC pattern   Another use for DTOs can be to encapsulate parameters for method calls  This can be useful if a method takes more than 4 or 5 parameters   When using the DTO pattern  you would also make use of DTO assemblers  The assemblers are used to create DTOs from Domain Objects  and vice versa   The conversion from Domain Object to DTO and back again can be a costly process  If you re not creating a distributed application  you probably won t see any great benefits from the pattern  as Martin Fowler explains here

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With MVC data transfer objects are often used to map domain models to simpler objects that will ultimately get displayed by the view   From Wikipedia      Data transfer object  DTO   formerly known as value objects or VO  is   a design pattern used to transfer data between software application   subsystems  DTOs are often used in conjunction with data access   objects to retrieve data from a database

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