How to fetch FetchType LAZY associations with JPA and Hibernate in a Spring Controller

Question

I have a Person class    Entity public class Person         Id      GeneratedValue     private Long id        ManyToMany fetch   FetchType LAZY      private List lt Role gt  roles         etc     With a many-to-many relation that is lazy   In my controller I have   Controller  RequestMapping   person   public class PersonController        Autowired     PersonRepository personRepository        RequestMapping   get       public  ResponseBody Person getPerson             Person person   personRepository findOne 1L           return person            And the PersonRepository is just this code  written according to this guide  public interface PersonRepository extends JpaRepository lt Person  Long gt        However  in this controller I actually need the lazy-data  How can I trigger its loading   Trying to access it will fail with      failed to lazily initialize a collection of role    no dusken momus model Person roles  could not initialize proxy - no   Session   or other exceptions depending on what I try   My xml-description  in case needed   Thanks

User · Answer

I think you need OpenSessionInViewFilter to keep your session open during view rendering  but it is not too good practice

User · Answer

Spring Data JpaRepository  The Spring Data JpaRepository defines the following two methods    getOne  which returns an entity proxy that is suitable for setting a  ManyToOne or  OneToOne parent association when persisting a child entity  findById  which returns the entity POJO after running the SELECT statement that loads the entity from the associated table   However  in your case  you didn t call either getOne or findById   Person person   personRepository findOne 1L     So  I assume the findOne method is a method you defined in the PersonRepository  However  the findOne method is not very useful in your case  Since you need to fetch the Person along with is roles collection  it s better to use a findOneWithRoles method instead   Custom Spring Data methods  You can define a PersonRepositoryCustom interface  as follows   public interface PersonRepository     extends JpaRepository lt Person  Long gt   PersonRepositoryCustom        public interface PersonRepositoryCustom       Person findOneWithRoles Long id       And define its implementation like this   public class PersonRepositoryImpl implements PersonRepositoryCustom         PersistenceContext     private EntityManager entityManager        Override     public Person findOneWithRoles Long id              return entityManager createQuery                 select p              from Person p             left join fetch p roles             where p id    id                   Person class           setParameter  id   id           getSingleResult              That s it

User · Answer

You can do the same like this    Override public FaqQuestions getFaqQuestionById Long questionId        session   sessionFactory openSession        tx   session beginTransaction        FaqQuestions faqQuestions   null      try           faqQuestions    FaqQuestions  session get FaqQuestions class                  questionId           Hibernate initialize faqQuestions getFaqAnswers              tx commit            faqQuestions getFaqAnswers   size          finally           session close              return faqQuestions      Just use faqQuestions getFaqAnswers   size  nin your controller and you will get the size if lazily intialised list  without fetching the list itself

User · Answer

You will have to make an explicit call on the lazy collection in order to initialize it  common practice is to call  size   for this purpose   In Hibernate there is a dedicated method for this  Hibernate initialize     but JPA has no equivalent of that  Of course you will have to make sure that the invocation is done  when the session is still available  so annotate your controller method with  Transactional  An alternative is to create an intermediate Service layer between the Controller and the Repository that could expose methods which initialize lazy collections  Update  Please note that the above solution is easy  but results in two distinct queries to the database  one for the user  another one for its roles   If you want to achieve better performace add the following method to your Spring Data JPA repository interface  public interface PersonRepository extends JpaRepository lt Person  Long gt          Query  quot SELECT p FROM Person p JOIN FETCH p roles WHERE p id     id  quot       public Person findByIdAndFetchRolesEagerly  Param  quot id quot   Long id       This method will use JPQL s fetch join clause to eagerly load the roles association in a single round-trip to the database  and will therefore mitigate the performance penalty incurred by the two distinct queries in the above solution

User · Answer

it can only be lazily loaded whilst within a transaction  So you could access the collection in your repository  which has a transaction - or what I normally do is a get with association  or set fetchmode to eager

User · Answer

Though this is an old post  please consider using  NamedEntityGraph  Javax Persistence  and  EntityGraph  Spring Data JPA   The combination works   Example   Entity  Table name    Employee   schema    dbo   catalog    ARCHO    NamedEntityGraph name    employeeAuthorities               attributeNodes    NamedAttributeNode  employeeGroups    public class EmployeeEntity implements Serializable  UserDetails      your props     and then the spring repo as below   RepositoryRestResource collectionResourceRel    Employee   path    Employee   public interface IEmployeeRepository extends PagingAndSortingRepository lt EmployeeEntity  String gt                    EntityGraph value    employeeAuthorities   type   EntityGraphType LOAD      EmployeeEntity getByUsername String userName

User · Answer

You have some options   Write a method on repository that return a initialized entity as R J suggested     More work  best performance    Use OpenEntityManagerInViewFilter to keep session open for the entire request    Less work  usually acceptable in web enviroments    Use a helper class to initialize entities when required    Less work  useful when OEMIV is not at option  for example in a Swing application  but may be useful too on repository implementations to initialize any entity in one shot   For the last option  I wrote a utility class  JpaUtils to initilize entities at some deph   For example    Transactional public class RepositoryHelper         PersistenceContext     private EntityManager em       public void intialize Object entity  int depth            JpaUtils initialize em  entity  depth

[java] How to fetch FetchType.LAZY associations with JPA and Hibernate in a Spring Controller

Examples related to java

Examples related to spring

Examples related to hibernate

Examples related to jpa

Examples related to spring-data