How to solve the failed to lazily initialize a collection of role Hibernate exception

Question

I have this problem      org hibernate LazyInitializationException  failed to lazily initialize a collection of role  mvc3 model Topic comments  no session or session was closed   Here is the model      Entity  Table name    T TOPIC   public class Topic         Id      GeneratedValue strategy GenerationType AUTO      private int id        ManyToOne      JoinColumn name  USER ID       private User author        Enumerated EnumType STRING          private Tag topicTag       private String name      private String text        OneToMany mappedBy    topic   cascade   CascadeType ALL      private Collection lt Comment gt  comments   new LinkedHashSet lt Comment gt                   public Collection lt Comment gt  getComments                return comments             The controller  which calls model looks like the following    Controller  RequestMapping value     topic   public class TopicController         Autowired     private TopicService service       private static final Logger logger   LoggerFactory getLogger TopicController class          RequestMapping value     details  topicId    method   RequestMethod GET      public ModelAndView details  PathVariable value  topicId   int id                     Topic topicById   service findTopicByID id               Collection lt Comment gt  commentList   topicById getComments                 Hashtable modelData   new Hashtable                modelData put  topic   topicById               modelData put  commentList   commentList                return new ModelAndView   topic details   modelData                The jsp-page looks li the following    lt   page import  com epam mvc3 helpers Utils   gt   lt    page language  java  contentType  text html  charset UTF-8  pageEncoding  UTF-8   gt   lt    taglib uri  http   java sun com jsp jstl core  prefix  c    gt   lt    page session  false    gt   lt html gt   lt head gt         lt title gt View Topic lt  title gt   lt  head gt   lt body gt    lt ul gt   lt c forEach items    commentList   var  item  gt   lt jsp useBean id  item  type  mvc3 model Comment   gt   lt li gt   item getText    lt  li gt    lt  c forEach gt   lt  ul gt   lt  body gt   lt  html gt    Exception is rised  when viewing jsp  In the line with c forEach loop

User · Answer

To get rid of lazy initialization exception you should not call for lazy collection when you operate with detached object.

From my opinion, best approach is to use DTO, and not entity. In this case you can explicitly set fields which you want to use. As usual it's enough. No need to worry that something like jackson ObjectMapper, or hashCode generated by Lombok will call your methods implicitly.

For some specific cases you can use @EntityGrpaph annotation, which allow you to make eager load even if you have fetchType=lazy in your entity.

User · Answer

The problem is caused because the code is accessing a lazy JPA relation when the  connection  to the database is closed  persistence context is the correct name in terms of Hibernate JPA    A simple way of solving it in Spring Boot is by defining a service layer and using the  Transactional annotation  This annotation in a method creates a transaction that propagates into the repository layer and keeps open the persistence context until the method finish  If you access the collection inside the transactional method Hibernate JPA will fetch the data from the database   In your case  you just need to annotate with  Transactional the method findTopicByID id  in your TopicService and force the fetch of the collection in that method  for instance  by asking its size         Transactional readOnly   true      public Topic findTopicById Long id            Topic topic   TopicRepository findById id  orElse null           topic getComments   size            return topic

User · Answer

Not the best solution  but for those who are facing LazyInitializationException especially on Serialization this will help  Here you will check lazily initialized properties and setting null to those  For that create the below class  public class RepositoryUtil       public static final boolean isCollectionInitialized Collection lt   gt  collection            if  collection instanceof PersistentCollection              return   PersistentCollection  collection  wasInitialized            else              return true               Inside your Entity class which you are having lazily initialized properties add a method like shown below  Add all your lazily loading properties inside this method   public void checkLazyIntialzation         if   RepositoryUtil isCollectionInitialized yourlazyproperty             yourlazyproperty  null          Call this checkLazyIntialzation   method after on all the places where you are loading data       YourEntity obj  entityManager find YourEntity class 1L     obj checkLazyIntialzation

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By using the hibernate  Transactional annotation  if you get an object from the database with lazy fetched attributes  you can simply get these by fetching these attributes like this     Transactional public void checkTicketSalePresence UUID ticketUuid  UUID saleUuid            Optional lt Ticket gt  savedTicketOpt   ticketRepository findById ticketUuid           savedTicketOpt ifPresent ticket - gt                Optional lt Sale gt  saleOpt   ticket getSales   stream   filter sale - gt  sale getUuid      saleUuid  findFirst                assertThat saleOpt  isPresent                    Here  in an Hibernate proxy-managed transaction  the fact of calling ticket getSales   do another query to fetch sales because you explicitly asked it

User · Answer

The reason is you are trying to get the commentList on your controller after closing the session inside the service   topicById getComments      Above will load the commentList only if your hibernate session is active  which I guess you closed in your service   So  you have to get the commentList before closing the session

User · Answer

In my case following code was a problem   entityManager detach topicById   topicById getComments      exception thrown   Because it detached from the database and Hibernate no longer retrieved list from the field when it was needed  So I initialize it before detaching   Hibernate initialize topicById getComments     entityManager detach topicById   topicById getComments      works like a charm

User · Answer

If you are trying to have a relation between a entity and a Collection or a List of java objects  for example Long type   it would like something like this    ElementCollection fetch   FetchType EAGER      public List lt Long gt  ids

User · Answer

The reason is that when you use lazy load  the session is closed   There are two solutions    Don t use lazy load   Set lazy false in XML or Set  OneToMany fetch   FetchType EAGER  In annotation  Use lazy load    Set lazy true in XML or Set  OneToMany fetch   FetchType LAZY  In annotation   and add OpenSessionInViewFilter filter in your web xml   Detail See my POST

User · Answer

The problem is caused by accessing an attribute with the hibernate session closed  You have not a hibernate transaction in the controller   Possible solutions    Do all this logic  in the service layer   with the  Transactional   not in the controller  There should be the right place to do this  it is part of the logic of the app  not in the controller  in this case  an interface to load the model   All the operations in the service layer should be transactional  i e   Move this line to the TopicService findTopicByID method   Collection commentList   topicById getComments    Use  eager  instead of  lazy   Now you are not using  lazy     it is not a real solution  if you want to use lazy  works like a temporary  very temporary  workaround  use  Transactional in the Controller  It should not be used here  you are mixing service layer with presentation  it is not a good design  use OpenSessionInViewFilter  many disadvantages reported  possible instability    In general  the best solution is the 1

User · Answer

The collection comments in your model class Topic is lazily loaded  which is the default behaviour if you don t annotate it with fetch   FetchType EAGER specifically   It is mostly likely that your findTopicByID service is using a stateless Hibernate session  A stateless session does not have the first level cache  i e   no persistence context  Later on when you try to iterate comments  Hibernate will throw an exception   org hibernate LazyInitializationException  failed to lazily initialize a collection of role  mvc3 model Topic comments  no session or session was closed   The solution can be    Annotate comments with fetch   FetchType EAGER   OneToMany fetch   FetchType EAGER  mappedBy    topic   cascade   CascadeType ALL     private Collection lt Comment gt  comments   new LinkedHashSet lt Comment gt      If you still would like comments to be lazily loaded  use Hibernate s stateful sessions  so that you ll be able to fetch comments later on demand

User · Answer

I found out that declaring  PersistenceContext as EXTENDED also solves this problem    PersistenceContext type   PersistenceContextType EXTENDED

User · Answer

your list is lazy loading  so the list wasn t loaded  call to get on the list is not enough  use in Hibernate initialize in order to init the list  If dosnt work run on the list element and call Hibernate initialize for each   this need to be before you return from the transaction scope  look at this post  search for  -   Node n         get the node Hibernate initialize n      initializes  parent  similar to getParent  Hibernate initialize n getChildren        pass the lazy collection into the session

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Hi All posting quite late hope it helps others  Thanking in advance to  GMK for this post  Hibernate initialize object   when Lazy  true   Set lt myObject gt  set null  hibernateSession open set hibernateSession getMyObjects    hibernateSession close      now if i access  set  after closing session it throws exception   My solution    Set lt myObject gt  set new HashSet lt myObject gt     hibernateSession open set addAll hibernateSession getMyObjects     hibernateSession close      now i can access  set  even after closing Hibernate Session

User · Answer

Two things you should have for fetch   FetchType LAZY    Transactional   and  Hibernate initialize topicById getComments

User · Answer

In my case  I had the mapping b w A and B like   A has    OneToMany mappedBy    a   cascade   CascadeType ALL  Set lt B gt  bs    in the DAO layer  the method needs to be annotated with  Transactional if you haven t annotated the mapping with Fetch Type - Eager

User · Answer

Yet another way to do the thing  you can use TransactionTemplate to wrap around the lazy fetch  Like   Collection lt Comment gt  commentList   this transactionTemplate execute  status - gt  topicById getComments

User · Answer

it was the problem i recently faced which i solved with using    lt f attribute name  collectionType  value  java util ArrayList    gt    more detailed decription here and this saved my day

User · Answer

To solve the problem in my case it was just missing this line   lt tx annotation-driven transaction-manager  myTxManager    gt    in the application-context file   The  Transactional annotation over a method was not taken into account   Hope the answer will help someone

User · Answer

Transactional annotation on controller is missing   Controller  RequestMapping       Transactional public class UserController

User · Answer

One of the best solutions is to add the following in your application properties file  spring jpa properties hibernate enable lazy load no trans true

User · Answer

I know it s an old question but I want to help  You can put the transactional annotation on the service method you need  in this case findTopicByID id  should have   Transactional propagation Propagation REQUIRED  readOnly true  noRollbackFor Exception class    more info about this annotation can be found here  About the other solutions   fetch   FetchType EAGER    is not a good practice  it should be used ONLY if necessary   Hibernate initialize topics getComments       The hibernate initializer binds your classes to the hibernate technology  If you are aiming to be flexible is not a good way to go   Hope it helps

User · Answer

The origin of your problem   By default hibernate lazily loads the collections  relationships  which means whenver you use the collection in your code here comments field in Topic class  the hibernate gets that from database  now the problem is that you are getting the collection in your controller  where the  JPA session is closed  This is the line of code that causes the exception  where you are loading the comments collection         Collection lt Comment gt  commentList   topicById getComments      You are  getting  comments  collection  topic getComments    in your controller where JPA session has ended  and that causes the exception  Also if you had got  the comments collection in your jsp file like this instead of getting it in your controller      lt c forEach items  topic comments  var  item  gt    some code  lt  c forEach gt    You would still have the same exception for the same reason   Solving the problem   Because you just can have only two collections with the FetchType Eager eagerly fetched collection  in an Entity class and because lazy loading is more efficient than eagerly loading  I think this way of solving your problem is better than just changing the FetchType to eager   If you want to have collection lazy initialized  and also make this work  it is better to add this snippet of code to your web xml     lt filter gt       lt filter-name gt SpringOpenEntityManagerInViewFilter lt  filter-name gt       lt filter-class gt org springframework orm jpa support OpenEntityManagerInViewFilter lt  filter-class gt   lt  filter gt   lt filter-mapping gt       lt filter-name gt SpringOpenEntityManagerInViewFilter lt  filter-name gt       lt url-pattern gt    lt  url-pattern gt   lt  filter-mapping gt    What this code does is that it will increase the length of your JPA session or as the documentation says  it is used  to allow for lazy loading in web views despite the original transactions already being completed   so  this way the JPA session will be open a bit longer and because of that you can lazily load collections in your jsp files and controller classes

User · Answer

Controller  RequestMapping value     topic    Transactional   i solve this problem by adding  Transactional i think this can make session open

User · Answer

For those working with Criteria  I found that   criteria setFetchMode  lazily fetched member   FetchMode EAGER     did everything I needed had done   Initial fetch mode for collections is set to FetchMode LAZY to provide performance  but when I need the data  I just add that line and enjoy the fully populated objects

User · Answer

The best way to handle the LazyInitializationException is to fetch it upon query time  like this  select t from Topic t left join fetch t comments  You should ALWAYS avoid the following anti-patterns   FetchType EAGER OSIV  Open Session in View  hibernate enable lazy load no trans Hibernate configuration property  Therefore  make sure that your FetchType LAZY associations are initialized at query time or within the original  Transactional scope using Hibernate initialize for secondary collections

User · Answer

There are multiple solution for this Lazy Initialisation issue -   1  Change the association Fetch type from LAZY to EAGER but this is not a good practice because this will degrade the performance   2  Use FetchType LAZY on associated Object and also use Transactional annotation in your service layer method so that session will remain open and when you will call topicById getComments    child object comments  will get loaded   3  Also  please try to use DTO object instead of entity in controller layer  In your case  session is closed at controller layer  SO better to convert entity to DTO in service layer

User · Answer

i resolved using List instead of Set   private List lt Categories gt  children   new ArrayList lt Categories gt

User · Answer

In order to lazy load a collection there must be an active session   In a web app there are two ways to do this   You can use the Open Session In View pattern  where you use an interceptor to open the session at the beginning of the request and close it at the end   The risk there is that you have to have solid exception handling or you could bind up all your sessions and your app could hang     The other way to handle this is to collect all the data you need in your controller  close your session  and then stuff the data into your model   I personally prefer this approach  as it seems a little closer to the spirit of the MVC pattern   Also if you get an error from the database this way you can handle it a lot better than if it happens in your view renderer   Your friend in this scenario is Hibernate initialize myTopic getComments      You will also have to reattach the object to the session  since you re creating a new transaction with every request   Use session lock myTopic LockMode NONE  for that

User · Answer

If you know that you ll want to see all Comments every time you retrieve a Topic then change your field mapping for comments to    OneToMany fetch   FetchType EAGER  mappedBy    topic   cascade   CascadeType ALL  private Collection lt Comment gt  comments   new LinkedHashSet lt Comment gt       Collections are lazy-loaded by default  take a look at this if you want to know more

User · Answer

From my experience  I have the following methods to solved the famous LazyInitializationException    1  Use Hibernate initialize  Hibernate initialize topics getComments        2  Use JOIN FETCH  You can use the JOIN FETCH syntax in your JPQL to explicitly fetch the child collection out  This is some how like EAGER fetching    3  Use OpenSessionInViewFilter  LazyInitializationException often occur in view layer  If you use Spring framework  you can use OpenSessionInViewFilter  However  I do not suggest you to do so  It may leads to performance issue if not use correctly

[java] How to solve the “failed to lazily initialize a collection of role” Hibernate exception

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