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map DTO to Backend Entities

I am developing a rest application where the data in DB is loaded in Entities then some transformations are made on the data while being filled in corresponding DTOs then returned back to the consumer.
According to the consumer and some other parameters, a different subset of the data should be returned to the user, for example if user is inquiring on his personal info, level of details returning will be different than if a manager is inquiring on the data of his employees, etc ...
My question:
Is there any framework to handle this custom mapping (i.e. an xml based file that determines which field in which BE Entity should be mapped to which DTO in which condition ? instead of making a custom code in each case? thanks in advance.
I am using spring rest + hibernate

About XML file mapping, I do not know any. But what I find really useful and very customizable is MapStruct. It is a very useful library and the docs and examples are very good.
A simple example:
#Mapper
public interface CarMapper {
CarMapper INSTANCE = Mappers.getMapper( CarMapper.class );
#Mapping(source = "numberOfSeats", target = "seatCount") // Here is one of the functionalities that you wanted...
CarDto carToCarDto(Car car);
}
And there is IDE and Lombok support also.

Converting Request body to DTO with different fields structure in Spring Web app

Spring Web works perfectly in scenarios when rest controller takes a custom object, entity or dto, as parameter of handler method. You just need to annotate it with #RequestBody annotation. But how can I handle cases when the object has different field names or structure? I.e. for request json like
{"name":"FirstName", "address" : { "city" : "Rome" }}
to 'flattened' structure like
class Person { private String name; private String city; }
Is it possible to create a custom converter like HttpConverter, but for specific controller handler method only?

I think the easies way is to make a DTO matching the structure of the incomming json so Spring can map the json to this DTO. Then you can map this DTO to your Person class in your controller.
If your mapping is simple it is easiest to just write the mapping yourself. If not you can use a mapping tool like https://github.com/mapstruct/mapstruct or http://modelmapper.org/.
Please let me know if this is usefull.

DDD implementation with Spring Data and JPA + Hibernate problem with identities

So I'm trying for the first time in a not so complex project to implement Domain Driven Design by separating all my code into application, domain, infrastructure and interfaces packages.
I also went with the whole separation of the JPA Entities to Domain models that will hold my business logic as rich models and used the Builder pattern to instantiate. This approach created me a headache and can't figure out if Im doing it all wrong when using JPA + ORM and Spring Data with DDD.
Process explanation
The application is a Rest API consumer (without any user interaction) that process daily through Scheduler tasks a fairly big amount of data resources and stores or updates into MySQL. Im using RestTemplate to fetch and convert the JSON responses into Domain objects and from there Im applying any business logic within the Domain itself e.g. validation, events, etc
From what I have read the aggregate root object should have an identity in their whole lifecycle and should be unique. I have used the id of the rest API object because is already something that I use to identify and track in my business domain. I have also created a property for the Technical id so when I convert Entities to Domain objects it can hold a reference for the update process.
When I need to persist the Domain to the data source (MySQL) for the first time Im converting them into Entity objects and I persist them using the save() method. So far so good.
Now when I need to update those records in the data source I first fetch them as a List of Employees from data source, convert Entity objects to Domain objects and then I fetch the list of Employees from the rest API as Domain models. Up until now I have two lists of the same Domain object types as List<Employee>. I'm iterating them using Streams and checking if an objects are not equal() between them if yes a collection of List items is created as a third list with Employee objects that need to be updated. Here I've already passed the technical Id to the domain objects in the third list of Employees so Hibernate can identify and use to update the records that are already exists.
Up to here are all fairly simple stuff until I use the saveAll() method to update the records.
Questions
I alway see Hibernate using INSERT instead of updating the list of
records. So If Im correct Hibernate session is not recognising the
objects that Im throwing into it because I have detached them when I
used the convert to domain object?
Does anyone have a better idea how can I implement this differently or fix
this problem?
Or should I stop using this approach as two different objects and continue use
them as rich Entity models?
Simple classes to explain it with code
EmployeeDO.java
#Entity
#Table(name = "employees")
public class EmployeeDO implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
public EmployeeDO() {}
...omitted getter/setters
}
Employee.java
public class Employee {
private Long persistId;
private Long employeeId;
private String name;
private Employee() {}
...omitted getters and Builder
}
EmployeeConverter.java
public class EmployeeConverter {
public static EmployeeDO serialize(Employee employee) {
EmployeeDO target = new EmployeeDO();
if (employee.getPersistId() != null) {
target.setId(employee.getPersistId());
}
target.setName(employee.getName());
return target;
}
public static Employee deserialize(EmployeeDO employee) {
return new Country.Builder(employee.getEmployeeId)
.withPersistId(employee.getId()) //<-- Technical ID setter
.withName(employee.getName())
.build();
}
}
EmployeeRepository.java
#Component
public class EmployeeReporistoryImpl implements EmployeeRepository {
#Autowired
EmployeeJpaRepository db;
#Override
public List<Employee> findAll() {
return db.findAll().stream()
.map(employee -> EmployeeConverter.deserialize(employee))
.collect(Collectors.toList());
}
#Override
public void saveAll(List<Employee> employees) {
db.saveAll(employees.stream()
.map(employee -> EmployeeConverter.serialize(employee))
.collect(Collectors.toList()));
}
}
EmployeeJpaRepository.java
#Repository
public interface EmployeeJpaRepository extends JpaRepository<EmployeeDO, Long> {
}

I use the same approach on my project: two different models for the domain and the persistence.
First, I would suggest you to don't use the converter approach but use the Memento pattern. Your domain entity exports a memento object and it could be restored from the same object. Yes, the domain has 2 functions that aren't related to the domain (they exist just to supply a non-functional requirement), but, on the other side, you avoid to expose functions, getters and constructors that the domain business logic never use.
For the part about the persistence, I don't use JPA exactly for this reason: you have to write a lot of code to reload, update and persist the entities correctly. I write directly SQL code: I can write and test it fast, and once it works I'm sure that it does what I want. With the Memento object I can have directly what I will use in the insert/update query, and I avoid myself a lot of headaches about the JPA of handling complex tables structures.
Anyway, if you want to use JPA, the only solution is to:
load the persistence entities and transform them into domain entities
update the domain entities according to the changes that you have to do in your domain
save the domain entities, that means:
reload the persistence entities
change, or create if there're new ones, them with the changes that you get from the updated domain entities
save the persistence entities
I've tried a mixed solution, where the domain entities are extended by the persistence ones (a bit complex to do). A lot of care should be took to avoid that domain model should adapts to the restrictions of JPA that come from the persistence model.
Here there's an interesting reading about the splitting of the two models.
Finally, my suggestion is to think how complex the domain is and use the simplest solution for the problem:
is it big and with a lot of complex behaviours? Is expected that it will grow up in a big one? Use two models, domain and persistence, and manage the persistence directly with SQL It avoids a lot of caos in the read/update/save phase.
is it simple? Then, first, should I use the DDD approach? If really yes, I would let the JPA annotations to split inside the domain. Yes, it's not pure DDD, but we live in the real world and the time to do something simple in the pure way should not be some orders of magnitude bigger that the the time I need to to it with some compromises. And, on the other side, I can write all this stuff in an XML in the infrastructure layer, avoiding to clutter the domain with it. As it's done in the spring DDD sample here.

When you want to update an existing object, you first have to load it through entityManager.find() and apply the changes on that object or use entityManager.merge since you are working with detached entities.
Anyway, modelling rich domain models based on JPA is the perfect use case for Blaze-Persistence Entity Views.
Blaze-Persistence is a query builder on top of JPA which supports many of the advanced DBMS features on top of the JPA model. I created Entity Views on top of it to allow easy mapping between JPA models and custom interface defined models, something like Spring Data Projections on steroids. The idea is that you define your target structure the way you like and map attributes(getters) via JPQL expressions to the entity model. Since the attribute name is used as default mapping, you mostly don't need explicit mappings as 80% of the use cases is to have DTOs that are a subset of the entity model.
The interesting point here is that entity views can also be updatable and support automatic translation back to the entity/DB model.
A mapping for your model could look as simple as the following
#EntityView(EmployeeDO.class)
#UpdatableEntityView
interface Employee {
#IdMapping("persistId")
Long getId();
Long getEmployeeId();
String getName();
void setName(String name);
}
Querying is a matter of applying the entity view to a query, the simplest being just a query by id.
Employee dto = entityViewManager.find(entityManager, Employee.class, id);
The Spring Data integration allows you to use it almost like Spring Data Projections: https://persistence.blazebit.com/documentation/entity-view/manual/en_US/index.html#spring-data-features and it can also be saved back. Here a sample repository
#Repository
interface EmployeeRepository {
Employee findOne(Long id);
void save(Employee e);
}
It will only fetch the mappings that you tell it to fetch and also only update the state that you make updatable through setters.
With the Jackson integration you can deserialize your payload onto a loaded entity view or you can avoid loading alltogether and use the Spring MVC integration to capture just the state that was transferred and flush that. This could look like the following:
#RequestMapping(path = "/employee/{id}", method = RequestMethod.PUT, consumes = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<String> updateEmp(#EntityViewId("id") #RequestBody Employee emp) {
employeeRepository.save(emp);
return ResponseEntity.ok(emp.getId().toString());
}
Here you can see an example project: https://github.com/Blazebit/blaze-persistence/tree/master/examples/spring-data-webmvc

hibernate DTO with a deviant database

I am building a spring boot application which uses REST services to deliver content to the front-end
But my DTO does not correspond to my database.
Here is a diagram of the database
And my DTO should look something like this
public class GlobeEntity extends BaseEntity {
// for all definition years
private List<Instance> instances;
class Instance {
// CountryInstance.definitionYear
private String definitionYear;
// for all countries
private List<Country> countries;
class Country {
// Country.countryId
String id;
// Country.externalIdentifier
String externalIdentifier;
// CountryInstanceCompatibility.total
String com;
// CountryInstanceUtility.total
String uti;
}
}
}
Is this possible to do with hibernate annotations?

For the DTO, what is turned into JSON when you return that class from a controller depends on your JSON serializer you have configured in Spring. Then you make use of the JSON annotations to have more control over what is returned.
Depending on how you do things, you may just choose to convert between an entity and a DTO, and have a class for each. Although this is a bit annoying because it does add allot of overhead of having more classes and other classes depending on the two, it can be come a real real mess if you use the same class for both DTO and Entity representations when they are very different. For instance if you use a method in your controller, it's not clear wether this is an entity or a DTO. There are many cases when you have a controller you return a response which is not a resource in a database.

Specify MongoDb collection name at runtime in Spring boot

I am trying to reuse my existing EmployeeRepository code (see below) in two different microservices to store data in two different collections (in the same database).
#Document(collection = "employee")
public interface EmployeeRepository extends MongoRepository<Employee, String>
Is it possible to modify #Document(collection = "employee") to accept runtime parameters? For e.g. something like #Document(collection = ${COLLECTION_NAME}).
Would you recommend this approach or should I create a new Repository?

This is a really old thread, but I will add some better information here in case someone else finds this discussion, because things are a bit more flexible than what the accepted answer claims.
You can use an expression for the collection name because spel is an acceptable way to resolve the collection name. For example, if you have a property in your application.properties file like this:
mongo.collection.name = my_docs
And if you create a spring bean for this property in your configuration class like this:
#Bean("myDocumentCollection")
public String mongoCollectionName(#Value("${mongo.collection.name}") final String collectionName) {
return collectionName
}
Then you can use that as the collection name for a persistence document model like this:
#Document(collection = "#{#myDocumentCollection}")
public class SomeModel {
#Id
private String id;
// other members and accessors/mutators
// omitted for brevity
}

It shouldn't be possible, the documentation states that the collection field should be collection name, therefore not an expression:
http://docs.spring.io/spring-data/data-mongodb/docs/current/api/org/springframework/data/mongodb/core/mapping/Document.html
As far as your other question is concerned - even if passing an expression was possible, I would recommend creating a new repository class - code duplication would not be bad and also your microservices may need to perform different queries and the single repository class approach would force you to keep query methods for all microservices within the same interface, which isn't very clean.
Take a look at this video, they list some very interesting approaches: http://www.infoq.com/presentations/Micro-Services

I used #environment.getProperty() to read from my application.yml. Like so :
application.yml:
mongodb:
collections:
dwr-suffix: dwr
Model:
#Document("Log-#{#environment.getProperty('mongodb.collections.dwr-suffix')}")
public class Log {
#Id
String logId;
...