How can I get actual child collection, when adding new one in separated transactional method, while updating parent.
I have spring boot app with hibernate/jpa and one-to-many unidirectional model:
parent:
#Entity
public class Deal {
private UUID id;
#OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
private List<Rate> rates;
....
}
child:
#Entity
public class Rate {
private UUID id;
....
}
And I have non transactional method for do some business logic by rest call:
public Deal applyDeal(UUID dealId) {
dealService.apply(dealId);
return dealService.getById(dealId);
}
Method apply in DealService has several methods in separate transactions (all methods doLogic() annotated with #Transactional(Propagation.REQUIRES_NEW):
public void apply(UUI dealId) {
someService1.do1Logic(...);
someService2.do2Logic(...);
someService3.do3Logic(...);
}
In do2Logic() I have some logic that adding new Rate entity to my parent entity with dealId and direct call of save method for Deal object.
#Transactional(Propagation.REQUIRES_NEW)
publid void do2Logic(...) {
...
var deal = dealService.getById(...);
deal.getRates().add(new Rate());
dealService.save(deal);
}
But when I get response from root method applyDeal the new child entity is absent.
If after that I will try to get this parent in separate rest call (getDeal) I get actual parent entity with new child in collection.
How to get actual child collection in parent response of applyDeal method?
I tried to make all logic in one #Transactional but it doesn't works.
I also don't understand why when I am try to get deal instance to return in applyDeal I get old data.
Thank you.
I guess you are running MySQL or MariaDB? These two database by default use the repeatable read transaction isolation level, which can cause this behavior. Try configuring the read committed isolation level instead, and/or remove the REQUIRES_NEW propagation if possible, since that will suspend an already running transaction to start a second one.
Related
I need to store normalized (i.e. without special characters etc.) variants of some of the String fields of some entities.
An example:
#Entity
public class Car {
#Id
private Long id;
private String make;
private String model;
#OneToMany(cascade = CascadeType.ALL, orphanRemoval = true)
#JoinColumn(name = "CAR_ID")
private Set<NormalizedField> normalizedFields = new HashSet();
private Set<NormalizedField> createNormalizedFields(Car car) {
Set<NormalizedField> normalized = normalize(car);
this.normalizedFields.clear();
this.normalizedFields.addAll(normalized);
}
// I would use this approach, but it doesn't allow
// changes to related entities.
// #PreCreate
// public void onCreate() {
// createNormalizedFields();
// }
}
#Entity
public class NormalizedField {
#Id
private Long id;
private String fieldName;
private String normalizedValue;
}
It would be convenient if the normalized values were automatically (re)created whenever the Car entity is persisted. Is there a way to trigger the creation method automatically?
Using #PrePersist, #PreUpdate... is obviously not an option as it doesn't allow changes to related entities.
Spring AOP is not used in the project, so I would rather avoid introducing it for now. But it's an option anyways.
The application is huge, and managing the normalized values 'manually' would require quite a bit of work, hence I leave it as the last option.
Going to post this half-answer here ('half' because it provides a workaround with restrictions).
In some cases org.hibernate.Interceptor can be used to manage child entities whenever the parent entity is changed.
But there are restrictions: the javadoc says Session is not to be used in the Interceptor. JPA repository methods, JPQL or HQL calls are intercepted by the same Interceptor in a loop. Even native queries get intercepted unless you set FlushMode.COMMIT or FlushMode.MANUAL (and maybe some other).
The above means you'll probably have to use the datasource directly. I don't remember exactly how, but Spring provides means to execute queries using datasource directly and within current transaction. In my case it was enough as I had to manage some technical child entities that didn't need a representation as an Entity.
I have a set of simple models like this (getters and setters omitted for brevity):
#Entity
public class Customer {
#Id
private Integer id;
}
#Entity
public class Order {
#Id
private Integer id;
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "customer_id")
private Customer customer;
}
I am trying to load an Order using a Spring JPA repository with a findById method, including the customer.
First I tried this:
#Transactional
Optional<Order> findById(Integer id) {
return repository.findById(id);
}
But when I tried to access Customer I got a LazyInitializationException: could not initialize proxy - no Session. So after referring to some other questions, I updated my method to be a bit uglier, but to explicitly call Hibernate.initialize:
#Transactional
Optional<Order> findById(Integer id) {
return repository.findById(id)
.map( order -> {
Hibernate.initialize(order.getCustomer());
return order;
);
}
But I still get org.hibernate.LazyInitializationException: could not initialize proxy - no Session. repository is a regular CrudRepository which provides the findById method out-of-the-box.
How can I initialize this lazily loaded child entity? My understanding is that the #Transactional indicates that I should still be within the transaction for the entirety of this method call. The only thing further downstream is the repository itself, which is just an interface, so I'm not sure how else to go about forcing the load of this child entity.
The Order entity and everything else in it is retrieved properly from the database; it's only when I try to get the lazy-loaded child entities that we start having issues.
The only way I managed to get this working was to write a custom hql method in the Repository using a left join fetch. While that works, it clutters up my repository with a method that is pretty much a duplicate of another and which I'm pretty sure I'm not actually supposed to need (so I would rather not do it this way.)
Spring-Boot 2.1.4.RELEASE, Spring 5.1.6.RELEASE, Hibernate 5.3.7.Final.
You have to define the method as public. See "Method visibility and #Transactional" in the spring docs.
This should work:
#Transactional
public Optional<Order> findById(Integer id) {
Optional<Order> order = repository.findById(id);
order.ifPresent(o -> Hibernate.initialize(o.getCustomer()));
return order;
}
I have a Spring Boot App with Spring Data JPA with hibernate and MySQL as the data store.
I have 3 layers in my application:
API Service
Application Service
Domain Service ( with Repository)
The role of Application Service is to convert hibernate-backed POJOs to DTOs given some business logic.
POJO
SchoolClass.java
#Column
Long id;
#Column
String name;
#OneToMany(fetch = FetchType.LAZY, mappedBy = "schoolClass")
List<Book> books;
#OneToMany(fetch = FetchType.LAZY, mappedBy = "schoolClass")
List<Student> students;
#OneToMany(fetch = FetchType.LAZY, mappedBy = "schoolClass")
List<Schedule> schedules;
Domain Service - My transaction boundary is at the Domain Service layer.
SchoolClassService.java
#Autowired
private SchoolClassRepository repository;
#Transactional(readOnly = true)
public SchoolClass getClassById(Long id) {
return repository.findById(id);
}
Application Service
SchoolClassAppService.java
#Autowired
private SchoolClassService domainService;
public SchoolClassDto getClassById(Long id) {
SchoolClass schoolClass = domainService.getClassById(id);
// convert POJO to DTO;
return SchoolClassDto;
}
My problem is that at times the child entities on SchoolClass are empty when I try to access them in SchoolClassAppService. Not all of them, but out of the three, two would work fine but the third one would be empty. I tried to mark the children lists to be eagerly fetched, but apparently only two collections can be eagerly fetched before Hibernate starts throwing exceptions and it also does not sound like good practice to always load all the objects. I do not get LazyInitializationException, just the list is empty.
I have tried to just call the getter on all lists in the domain service method before returning it just to load all data for the POJO but that does not seem like a clean practice.
Are there any patterns available which keep the transaction boundaries as close to the persistence layer as possible while still make it viable to process the data even after the transaction has been closed?
Not sure why your collections are sometimes empty, but maybe that just how the data is?
I created Blaze-Persistence Entity Views for exactly that use case. You essentially define DTOs for JPA entities as interfaces and apply them on a query. It supports mapping nested DTOs, collection etc., essentially everything you'd expect and on top of that, it will improve your query performance as it will generate queries fetching just the data that you actually require for the DTOs.
The entity views for your example could look like this
#EntityView(SchoolClass.class)
interface SchoolClassDto {
String getName();
List<BookDto> getBooks();
}
#EntityView(Book.class)
interface BookDto {
// Whatever data you need from Book
}
Querying could look like this
List<SchoolClassDto> dtos = entityViewManager.applySetting(
EntityViewSetting.create(SchoolClassDto.class),
criteriaBuilderFactory.create(em, SchoolClass.class)
).getResultList();
Just keep in mind that DTOs shouldn't just be copies your entities but should be designed to fit your specific use case.
I am currently in the middle of migrating my REST-Server to GraphQL (at least partly). Most of the work is done, but i stumbled upon this problem which i seem to be unable to solve: OneToMany relationships in a graphql query, with FetchType.LAZY.
I am using:
https://github.com/graphql-java/graphql-spring-boot
and
https://github.com/graphql-java/graphql-java-tools for the integration.
Here is an example:
Entities:
#Entity
class Show {
private Long id;
private String name;
#OneToMany(mappedBy = "show")
private List<Competition> competition;
}
#Entity
class Competition {
private Long id;
private String name;
#ManyToOne(fetch = FetchType.LAZY)
private Show show;
}
Schema:
type Show {
id: ID!
name: String!
competitions: [Competition]
}
type Competition {
id: ID!
name: String
}
extend type Query {
shows : [Show]
}
Resolver:
#Component
public class ShowResolver implements GraphQLQueryResolver {
#Autowired
private ShowRepository showRepository;
public List<Show> getShows() {
return ((List<Show>)showRepository.findAll());
}
}
If i now query the endpoint with this (shorthand) query:
{
shows {
id
name
competitions {
id
}
}
}
i get:
org.hibernate.LazyInitializationException: failed to lazily initialize
a collection of role: Show.competitions, could not initialize proxy -
no Session
Now i know why this error happens and what it means, but i don't really know were to apply a fix for this. I don't want to make my entites to eagerly fetch all relations, because that would negate some of the advantages of GraphQL. Any ideas where i might need to look for a solution?
Thanks!
My prefered solution is to have the transaction open until the Servlet sends its response. With this small code change your LazyLoad will work right:
import javax.servlet.Filter;
import org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter;
#SpringBootApplication
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
/**
* Register the {#link OpenEntityManagerInViewFilter} so that the
* GraphQL-Servlet can handle lazy loads during execution.
*
* #return
*/
#Bean
public Filter OpenFilter() {
return new OpenEntityManagerInViewFilter();
}
}
I solved it and should have read the documentation of the graphql-java-tools library more carefully i suppose.
Beside the GraphQLQueryResolver which resolves the basic queries i also needed a GraphQLResolver<T> for my Showclass, which looks like this:
#Component
public class ShowResolver implements GraphQLResolver<Show> {
#Autowired
private CompetitionRepository competitionRepository;
public List<Competition> competitions(Show show) {
return ((List<Competition>)competitionRepository.findByShowId(show.getId()));
}
}
This tells the library how to resolve complex objects inside my Showclass and is only used if the initially query requests to include the Competitionobjects. Happy new Year!
EDIT 31.07.2019: I since stepped away from the solution below. Long running transactions are seldom a good idea and in this case it can cause problems once you scale your application. We started to implement DataLoaders to batch queries in an async matter. The long running transactions in combination with the async nature of the DataLoaders can lead to deadlocks: https://github.com/graphql-java-kickstart/graphql-java-tools/issues/58#issuecomment-398761715 (above and below for more information). I will not remove the solution below, because it might still be good starting point for smaller applications and/or applications which will not need any batched queries, but please keep this comment in mind when doing so.
EDIT: As requested here is another solution using a custom execution strategy. I am using graphql-spring-boot-starter and graphql-java-tools:
Create a Bean of type ExecutionStrategy that handles the transaction, like this:
#Service(GraphQLWebAutoConfiguration.QUERY_EXECUTION_STRATEGY)
public class AsyncTransactionalExecutionStrategy extends AsyncExecutionStrategy {
#Override
#Transactional
public CompletableFuture<ExecutionResult> execute(ExecutionContext executionContext, ExecutionStrategyParameters parameters) throws NonNullableFieldWasNullException {
return super.execute(executionContext, parameters);
}
}
This puts the whole execution of the query inside the same transaction. I don't know if this is the most optimal solution, and it also already has some drawbacks in regards to error handling, but you don't need to define a type resolver that way.
Notice that if this is the only ExecutionStrategy Bean present, this will also be used for mutations, contrary to what the Bean name might suggest. See https://github.com/graphql-java-kickstart/graphql-spring-boot/blob/v11.1.0/graphql-spring-boot-autoconfigure/src/main/java/graphql/kickstart/spring/web/boot/GraphQLWebAutoConfiguration.java#L161-L166 for reference. To avoid this define another ExecutionStrategy to be used for mutations:
#Bean(GraphQLWebAutoConfiguration.MUTATION_EXECUTION_STRATEGY)
public ExecutionStrategy queryExecutionStrategy() {
return new AsyncSerialExecutionStrategy();
}
For anyone confused about the accepted answer then you need to change the java entities to include a bidirectional relationship and ensure you use the helper methods to add a Competition otherwise its easy to forget to set the relationship up correctly.
#Entity
class Show {
private Long id;
private String name;
#OneToMany(cascade = CascadeType.ALL, mappedBy = "show")
private List<Competition> competition;
public void addCompetition(Competition c) {
c.setShow(this);
competition.add(c);
}
}
#Entity
class Competition {
private Long id;
private String name;
#ManyToOne(fetch = FetchType.LAZY)
private Show show;
}
The general intuition behind the accepted answer is:
The graphql resolver ShowResolver will open a transaction to get the list of shows but then it will close the transaction once its done doing that.
Then the nested graphql query for competitions will attempt to call getCompetition() on each Show instance retrieved from the previous query which will throw a LazyInitializationException because the transaction has been closed.
{
shows {
id
name
competitions {
id
}
}
}
The accepted answer is essentially
bypassing retrieving the list of competitions through the OneToMany relationship and instead creates a new query in a new transaction which eliminates the problem.
Not sure if this is a hack but #Transactional on resolvers doesn't work for me although the logic of doing that does make some sense but I am clearly not understanding the root cause.
For me using AsyncTransactionalExecutionStrategy worked incorrectly with exceptions. E.g. lazy init or app-level exception triggered transaction to rollback-only status. Spring transaction mechanism then threw on rollback-only transaction at the boundary of strategy execute, causing HttpRequestHandlerImpl to return 400 empty response. See https://github.com/graphql-java-kickstart/graphql-java-servlet/issues/250 and https://github.com/graphql-java/graphql-java/issues/1652 for more details.
What worked for me was using Instrumentation to wrap the whole operation in a transaction: https://spectrum.chat/graphql/general/transactional-queries-with-spring~47749680-3bb7-4508-8935-1d20d04d0c6a
I am assuming that whenever you fetch an object of Show, you want all the associated Competition of the Show object.
By default the fetch type for all collections type in an entity is LAZY. You can specify the EAGER type to make sure hibernate fetches the collection.
In your Show class you can change the fetchType to EAGER.
#OneToMany(cascade=CascadeType.ALL,fetch=FetchType.EAGER)
private List<Competition> competition;
You just need to annotate your resolver classes with #Transactional. Then, entities returned from repositories will be able to lazily fetch data.
(Please feel free to edit the title after reading this question)
I have quite simple #ManyToOne bidirectional mapping between entities Parent and Child.
The list of children Collection<Child> children in Parent is never initialized so it should be null.
When using EntityManager.find(...) for previously persisted Parent and then getting the list from that Parent gives ArrayList even there are no children yet with this Parent and it is fine.
However if persisting or merging a new Parent in the same transaction collection of children will be null even if the persisted/merged Parent is fetched again with EntityManager.find(...).
So i wonder this different behavior and if it is happening only in my environment.
I assume it has something to do with the caching of entities: entity is found from cache and it is returned instead of fetching it from db AND the initialization of empty collections will happen only when fetched from db, maybe depending on the JPA implementation.
Is my assumption even near the truth and if not what is the reason ?
Entities and test cases below. My test environment listed in tags.
// using lombok
#Slf4j
#RunWith(Arquillian.class)
public class NoPersistTest {
#PersistenceContext
private EntityManager em;
#Deployment
public static final WebArchive deploy() {
WebArchive wa = ShrinkWrap.create(WebArchive.class, "test.war")
.addAsWebInfResource("test-persistence.xml", "persistence.xml").addClasses(Parent.class, Child.class);
return wa;
}
#Test
#Transactional
public void testWithPreviouslyPersistedParent() {
Parent parent = em.find(Parent.class, 1); // has no children in db
// before
Child child = new Child();
child.setParent(parent);
parent.getChildren().add(child);
log.info("type of Collection<Child> is {}", parent.getChildren().getClass().getName());
// above logs "type of Collection<Child> is
// org.apache.openjpa.util.java$util$ArrayList$proxy"
}
#Test(expected = NullPointerException.class)
#Transactional
public void testPersistingParentInSameTransaction() {
Parent parent = new Parent();
em.persist(parent);
Parent parent2 = em.find(Parent.class, parent.getId());
Child child = new Child();
child.setParent(parent2);
log.info("Collection<Child> is {}", parent2.getChildren());
// above logs Collection<Child> is null
parent2.getChildren().add(child);
}
#Test(expected = NullPointerException.class)
#Transactional
public void testMergingParentInSameTransaction() {
Parent parent = new Parent();
parent = em.merge(parent);
Parent parent2 = em.find(Parent.class, parent.getId());
Child child = new Child();
child.setParent(parent2);
log.info("Collection<Child> is {}", parent2.getChildren());
// logs Collection<Child> is null
parent2.getChildren().add(child);
}
}
#Entity #Getter #Setter
public class Parent {
#Id #GeneratedValue(strategy=GenerationType.IDENTITY)
private Long id;
#OneToMany(mappedBy="parent", cascade=CascadeType.ALL, orphanRemoval=true)
private Collection<Child> children;
private Date created = new Date(); // just to have something to persist
}
#Entity #Getter #Setter
public class Child {
#Id #GeneratedValue(strategy=GenerationType.IDENTITY)
private Long id;
private Date created = new Date(); // just to have something to persist
#ManyToOne(optional=false)
private Parent parent;
}
If you create the Parent the collection is not initialized because you don't do it. And also when persisting the Parent JPA will leave the collection as it is.
But when you read the Parent with Hibernate the collection will contain a proxy because toMany relationships are fetched LAZY and this proxy is used to fetch the children on demand.
My recommendation is to always initialize collection to avoid NullPointerExceptions. That's good programming style.
The answer below is correct, I'd just like to add some more information as I was asked to in a comment elsewhere.
JPA uses caching to avoid database hits where possible, and where a database hit is still required, caching avoids the cost of rebuilding objects and allows maintaining Identity - ensuring you get back the same A instance when traversing A->B->A circular references.
When you persist an entity, you are placing it in the EntityManager cache as a managed entity - calling find on that EntityManager will return you the same exact instance you just passed in.
A initialA = new A();
A managedA = em.persist(initialA);
managedA==initialA
The persist call itself will not change anything within your entity (except possibly the ID if a sequence that allows preallocation to be used), so any null references will still be null.
Eventually the transaction commits and depending on your provider, entities can be cached in a second level cache. I'll assume you aren't using it for the sake of brevity; unless you force the EM to refresh this instance (flush first if its a new one!) or read it in a separate EntityManager, you will always get that same instance back with any null references.
If you refresh it or otherwise cause it to be reloaded, your JPA provider is required to set everything in the object as it is in the database, according to your mappings. Since null isn't a persistable state for a collection mapping, that means it will either eagerly fetch your references, or place proxies in there for lazy relationships, causing you to find an empty collection.