I am currently wondering whether a particular use case could be elegantly addressed by using a default interface method inside a JPA repository.
Suppose we have the following entity and supporting types:
public enum Status {
STATUS_1,
STATUS_2,
STATUS_3
}
#Entity
#Getter // from lombok
#Setter // from lombok
public class SomeEntity {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;
#Column(name = "status")
private Status status;
}
I need to be able to query a list of SomeEntity based on combination of Status enumeration values.
With Spring JPA, its respective repository could look like this:
#Repository
public interface SomeRepository extends JpaRepository<SomeEntity, Integer> {
#Query("select s.id, ... from SomeEntity s where s.status in (:statuses)")
List<SomeEntity> getByStatuses(#Param("statuses") List<Status> statuses);
}
The particular combinations of statuses that must be passed, however is very much dependent on the domain of SomeEntity, and I'd like to "bake-in" those statuses in the repository call. Why in the repository -- currently the same repository is used from multiple services, and SomeEntity is updated as part of transactions dealing with other entities updated together according to the service's specifics. The particular getByStatuses calls are the same for all services, and we have duplicated code fragments looking roughly like this:
List<Status> statuses = Arrays.asList(Status.STATUS_1, Status.STATUS_3);
List<SomeEntity> entities = someRepository.getByStatuses(statueses);
....
I was wondering if I could extract the above fragment in a default method inside the repository and change my services to use that method instead:
#Repository
public interface SomeRepository extends JpaRepository<SomeEntity, Integer> {
#Query("select s.id, ... from SomeEntity s where s.status in (:statuses)")
List<SomeEntity> getByStatuses(#Param("statuses") List<Status> statuses);
default List<SomeEntity> getByRelevantStatuses() {
List<Status> relevantStatuses = Arrays.asList(Status.STATUS_1, Status.STATUS_3);
return this.getByStatuses(relevantStatuses);
}
}
My concerns are the "magic" behind the scenes which Spring will do, could it cause issues with an approach like the above?
It appears that the default interface method usage in the described scenario is working. I tried it and so far I have not seen any problems.
I'll still be happy to know if there are things to worry about, and if I find anything useful myself, I will update this post.
Related
I am currently building a REST service with Micronaut Data. I have defined two JPA entities, bounded by a bidirectional #OneToMany relationship, and lazy loading.
#Entity
#Getter
#Setter
public class ScoringEntity {
#Id
private String id;
#OneToMany(mappedBy = "scoring", fetch = FetchType.LAZY)
private Set<ContributionEntity> contributions;
}
#Entity
#Getter
#Setter
public class ContributionEntity {
#Id
private String id;
#ManyToOne(fetch = FetchType.LAZY)
#MapsId
private ScoringEntity scoring;
}
#Repository
public interface ScoringRepository extends GenericRepository<ScoringEntity, String> {
Page<ScoringEntity> findAll(Pageable pageable);
}
In the controller, I return a Mono which is set to call the repository, then perform a mapping to a DTO (Scoring).
#Get
public Mono<Page<Scoring>> getScoring(Pageable pageable) {
return Mono.fromCallable(() -> scoringRepository.findAll(pageable))
.map(scoringEntities -> scoringEntities.map(scoringMapper::mapScoring));
}
Everything works fine in the findAll() method, but things go south when the mapper
tries to access the contributions set :
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: ScoringEntity.contributions, could not initialize proxy - no Session
While I understand why this happens (the transaction probably ends with the repository method), I can't find a satisfying solution. Setting the relationship to eager loading works, but it
significantly decreases performance (and I've read elsewhere it would be a code smell, which I tend to believe).
Besides I can't imagine that reactive streams be incompatible with hibernate and lazy loading.
What would be the best practice in this situation ?
There are a few options:
Add #Join("contributions") annotation to your repository method
Add #EntityGraph ... annotation to your repository method
Do fetching and mapping in one method annotated #ReadOnly or #Transactional so the session is open when the mapper is called
In this case, having reactive streams doesn't make much sense. Just return Page from the controller annotated #ExecuteOn(TaskExecutors.IO).
Mapping the association as EAGER is usually a code smell. But if you have situations where you always need to load an association, you can do it via a query.
Instead of findAll, you would call:
#Repository
public interface ScoringRepository extends GenericRepository<ScoringEntity, String> {
#Query("select se from ScoringEntity se left fetch join se.contributions")
Page<ScoringEntity> findScoringWithContributions(Pageable pageable);
}
Besides I can't imagine that reactive streams be incompatible with hibernate and lazy loading.
In this case the problem is that you are trying to lazy load the association after the session has been closed.
I have an entity as
#Getter
#Setter
#Entity
#Table(name = "feature")
#JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})
public class Feature {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
#Column(name = "name")
private String name;
#Column(name = "description")
private String description;
#OneToMany(mappedBy = "featureId", fetch = FetchType.LAZY)
private transient Collection<FeatureComponent> components;
}
While in its Repository(Dao) file, I have
public interface FeatureDao extends JpaRepository<Feature, Integer> {
#Query("SELECT e FROM Feature e")
public List<Feature> getAll();
#Query("SELECT e FROM Feature e LEFT JOIN e.components fc WHERE e.id= :id")
public Feature getWithDetail(#Param("id") Integer id);
}
When I'm calling featureDao.getAll(); it returns all features but including components list filled and because of that, my response it being too large to load on client-side.
I'm unable to understand why it is happening when I'm using Lazy fetch mode and didn't mentioned joining with components in my getAll method.
Please help to resolve that issue,
Thanks in advance.
Just like #spOOm already mentioned I also suspect this is the side effect of Jackson Feature entity serialization into JSON triggering the load of all the components.
That is why using DTOs instead of plain Entities is usually advisable when returning data via a Controller. With DTOs, you clearly define whatever you want to include in the response to the caller. You can even reorganize your model so that it fits better the needs of the clients. You decouple your inner model and the model your API consumers know, making it possible to rework your inner model and still keep the same public model. You could have the following DTO.
public class FeatureSimpleDto {
private Integer id;
private String name;
private String description;
}
Then, in your Controller or Service (here you can find different opinions) you would basically convert your Feature entity into a FeatureSimpleDto that would be returned by your Controller. Here you can use mapping libraries such as MapStruct or you can do it on your own (I usually tend to prefer doing it on my own, one less dependency to rely on).
Using Lombok may be a problem, depending on the relationship between tables, try to create getters manually in entity classes.
Thanks to everyone for providing workarounds... But every work item requires lots of changes which were not possible for me...
Luckily I found a solution that is working fine for me... Better to post here...
Step-1: Add dependency in pom.xml file
<dependency>
<groupId>com.fasterxml.jackson.datatype</groupId>
<artifactId>jackson-datatype-hibernate5</artifactId>
</dependency>
Step-2: Add a 'Bean' for Hibernate Module
We can add bean in any file having #Configuration annotation... Even, we can add in Springboot main application file(where we have main method).
#Bean
public Module datatypeHibernateModule() {
return new Hibernate5Module();
}
That's it, Happy Coding...
I have a large entity-class with many, many fields and a projection-class which should be a part of the large one.
Everything works fine, except the #OneToMany field. The #OneToMany field should be a list of addresses, but when converting it to the projection-class I always get the error "Unable to locate appropriate constructor [...] Expected arguments are: long, [...], ***.entity.Address".
The converter is searching for a single address Object instead of a List of Address Objects, and I don't understand why. I use lombok #Data and #AllArgsConstructor, so Getter and Setter should be there.
#Entity
#Data
public class House implements Serializable {
#Id
#Column(name = "ID", precision = 5)
private Long id;
#OneToMany
#JoinColumn(name = "HouseID")
private List<Address> identAdressen;
}
/// ----------------
#Data
#AllArgsConstructor
public class HouseView {
private Long objnr;
private List<Address> identAdressen;
}
When I remove the "List" in the HouseView-class it works as long as there are only single addresses, but when there are multiple it crashes too.
I don't get it why he tries to find a HouseView-Constructor with an single address-object, when in both classes there are Lists of Addresses.
Let trying not using lombok and see if it works
Spring Data Projections do not support collections but I think this is a perfect use case for Blaze-Persistence Entity Views.
I created the library to allow easy mapping between JPA models and custom interface or abstract class defined models, something like Spring Data Projections on steroids. The idea is that you define your target structure(domain model) the way you like and map attributes(getters) via JPQL expressions to the entity model.
A DTO model for your use case could look like the following with Blaze-Persistence Entity-Views:
#EntityView(House.class)
public interface HouseView {
#IdMapping
Long getObjnr();
Set<AddressView> getIdentAddressen();
#EntityView(Address.class)
interface AddressView {
#IdMapping
Long getId();
String getName();
}
}
Querying is a matter of applying the entity view to a query, the simplest being just a query by id.
HouseView a = entityViewManager.find(entityManager, HouseView.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
Page<HouseView> findAll(Pageable pageable);
The best part is, it will only fetch the state that is actually necessary!
What you can do is to write custom query on HouseRepository as
#Query("SELECT new com.packagename.HouseView(hos) from House hos")
then house view class can be as follows
public class HouseView {
private Long objnr;
private List<Address> identAdressen;
public HouseView(House house) {
identAdressen = house.identAdressen;
}
}
Hope it will work :) You can add more fields into constructor from join tables if required. It might help others coming late on post.
So I've been using Spring Data Repositories most of the time. But I've reached a use-case where I cannot use my Spring Repository to retrieve the entity that I need to return to the client.
So I have my class ResourceEntity which is a Spring Data Entity. And I'd like to return this entity as a ResourceProjectioninterface.
#Getter
#Setter
#NoArgsConstructor
#Entity
public class ResourceEntity{
private Long id;
private String name;
private String anotherFieldThatIsNotInTheProjection;
}
public interface ResourceProjection {
Long getId();
String getName();
}
Usually with a Spring Repository, I'd define something like that :
public interface ResourceRepository extends PagingAndSortingRepository<ResourceEntity, Long> {
Optional<ResourceProjection> getById(Long id);
}
In this case I can't use the "automatic proxy" generated by Spring Data to automatically implement my projection with the entity's data.
So my question is : Is there a way to "manually" convert the entity to the projection ?
Another solution I thought of is returning the entity and using Jackson annotations like #JsonIgnore to prevent some of my data to be returned, but that is not optimal with the way my code was written.
Otherwise I can always create a DTO class that will fill up with the data from the Entity. But as I have already created my projection for other purposes, I would like avoid creating a second "DTO".
You can do the projection programmatically in this way:
import org.springframework.data.projection.ProjectionFactory;
import org.springframework.data.projection.SpelAwareProxyProjectionFactory;
//...
resourceEntity = //find resource
ProjectionFactory pf = new SpelAwareProxyProjectionFactory();
ResourceProjection rp = pf.createProjection(ResourceProjection.class, resourceEntity)
This is a perfect use case for Blaze-Persistence Entity Views.
I created the library 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.
A mapping for your model could look as simple as the following
#EntityView(ResourceEntity.class)
interface ResourceProjection {
#IdMapping
Long getId();
String getName();
}
Querying is a matter of applying the entity view to a query, the simplest being just a query by id.
ResourceProjection dto = entityViewManager.find(entityManager, ResourceProjection.class, id);
But 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
Implementing interface projection using native sql query
1. OurResourceEntity.java class
#Getter
#Setter
#NoArgsConstructor
#Entity
public class ResourceEntity{
private Long id;
private String name;
}
2. Creating projection Interface name ProjectedResource.java, which maps data collected by the SQL query from repository layer method
public interface ProjectedResource {
Long getId();
String getName();
String getAnotherProperty();
}
3. Creating Repository layer method: getProjectedResources()
We are considering the database table name is resource.
We are only fetching id and name here.But using interface projection we can change the properties name according to our desire.
#Query(name="select id, name, anotherProperty from resource", nativeQuery=true)
List<ProjectedResource> getProjectedResources();
Hope the issue will be resolved!
I was trying to learn Spring Framework and ran into a problem with saving entities into CRUD Repository. I had few Entities with automatic numeric ID generation and they work just fine, but then I tried to make a class with String being a primary key just like this:
#Entity
#Table(name = "USERS")
#Builder
public class User {
#Id
#Column(name = "USER_NAME", nullable = false)
#Getter #Setter
private String name;
#Column(name = "USER_PASS", nullable = false)
#Getter #Setter
private String pass;
}
First I was getting exceptions about this class not having a default constructor:
org.springframework.orm.jpa.JpaSystemException: No default constructor for entity: : com.company.Model.User; nested exception is org.hibernate.InstantiationException: No default constructor for entity: : com.company.Model.User
Already weird, but still I decided to change #Builder annotation into 2 constructors, one with both arguments and second with none. I tried to save the entity instance into CRUD Repository userDAO (which is nothing more than interface extending CRUDRepository) by the typical test:
User admin = new User("admin", "6aDcZ72k");
...
#Test
public void saveUserAndFindById() {
admin = userDAO.save(admin);
assertThat(userDAO.findById(admin.getName())).isEqualTo(admin);
}
The result was assertion failed because the saved entity had "Optional" type:
org.junit.ComparisonFailure:
Expected :com.company.Model.User#2c06b113
Actual :Optional[com.company.Model.User#2c06b113]
I know I'm doing something really wrong but can't figure this out. Or maybe there is a way to just prevent making it optional? There must be few other entities with the reference on this class, but these references obviously don't work because of the above issue.
First of all,jpa require the entity has a No Arguments Constructor cause it will create a instance first and then populate it.The easiest way is to add #NoArgumentsConstructor that offered by lombok on the entity class.
And then,Optional is used by spring data jpa in order to avoid NullPointException and in fact it be is useful actually.If you want to use the interface that Spring-data-jpa offered,then you have to use Optional too.You cloud look here for more info about Optional:link1,link2
By the way,I usually use it like:
ExampleEntity example=exampleRepository.findById(id).orElseThrow(()->new ExampleNotFoundException());
In this way,you dont need to deal with Optional or think about NullPointException.
or:
ExampleEntity example=exampleRepository.findById(id).orElse(null);
In this way if you cant find the target entity,then it will be null.So dont forget to check if the entity is null.
Hope it could help~~~
It is not your save(...) that is returning Optional but userDAO.findById(admin.getName(). According to the documentation, CrudReposiotry provides a findById() whose return type is Optional<T>.
public interface CrudRepository<T, ID extends Serializable>
extends Repository<T, ID> {
Optional<T> findById(ID primaryKey);
}
If you do not want Optional as return type, You will need to provide your own method to do that. For example:
public interface PeronRepository extends CrudRepository<Person, String> {
Person findById(String personId);
}