Hibernate best practice to pull all lazy collections

Question

What I have    Entity public class MyEntity      OneToMany cascade   CascadeType ALL  fetch   FetchType LAZY  orphanRemoval   true     JoinColumn name    myentiy id     private List lt Address gt  addreses      OneToMany cascade   CascadeType ALL  fetch   FetchType LAZY  orphanRemoval   true     JoinColumn name    myentiy id     private List lt Person gt  persons               public void handle         Session session   createNewSession       MyEntity entity    MyEntity  session get MyEntity class  entityId      proceed session      FLUSH  COMMIT  CLOSE session      Utils objectToJson entity     TROUBLES  because it can t convert to json lazy collections     What a problem   The problem is that I can t pull lazy collection after session has been closed  But I also can t not close a session in proceed method    What a solution  coarse solution    a  Before session is closed  force hibernate to pull lazy collections  entity getAddresses   size    entity getPersons   size            b  Maybe more ellegant way is to use  Fetch FetchMode SUBSELECT  annotation  Question   What is a best practice common way more ellegant way to do it  Means convert my object to JSON

User · Answer

There are some kind of misunderstanding about lazy collections in JPA-Hibernate. First of all let's clear that why trying to read a lazy collection throws exceptions and not just simply returns NULL for converting or further use cases?.

That's because Null fields in Databases especially in joined columns have meaning and not simply not-presented state, like programming languages. when you're trying to interpret a lazy collection to Null value it means (on Datastore-side) there is no relations between these entities and it's not true. so throwing exception is some kind of best-practice and you have to deal with that not the Hibernate.

So as mentioned above I recommend to :

Detach the desired object before modifying it or using stateless session for querying
Manipulate lazy fields to desired values (zero,null,etc.)

also as described in other answers there are plenty of approaches(eager fetch, joining etc.) or libraries and methods for doing that, but you have to setting up your view of what's happening before dealing with the problem and solving it.

User · Answer

Place the Utils objectToJson entity   call before session closing   Or you can try to set fetch mode and play with code like this  Session s       DetachedCriteria dc   DetachedCriteria forClass MyEntity class  add Expression idEq id    dc setFetchMode  innerTable   FetchMode EAGER   Criteria c   dc getExecutableCriteria s   MyEntity a    MyEntity c uniqueResult

User · Answer

It s probably not anywhere approaching a best practice  but I usually call a SIZE on the collection to load the children in the same transaction  like you have suggested  It s clean  immune to any changes in the structure of the child elements  and yields SQL with low overhead

User · Answer

Try use Gson library to convert objects to Json  Example with servlets       List lt Party gt  parties   bean getPartiesByIncidentId incidentId           String json               try               json   new Gson   toJson parties             catch  Exception ex                ex printStackTrace                      response setContentType  application json            response setCharacterEncoding  UTF-8            response getWriter   write json

User · Answer

Use Hibernate initialize   within  Transactional to initialize lazy objects     start Transaction        Hibernate initialize entity getAddresses           Hibernate initialize entity getPersons      end Transaction    Now out side of the Transaction you are able to get lazy objects    entity getAddresses   size    entity getPersons   size

User · Answer

if you using jpa repository   set properties put  hibernate enable lazy load no trans  true   to jpaPropertymap

User · Answer

You can use the  NamedEntityGraph annotation to your entity to create a loadable query that set which collections you want to load on your query   The main advantage of this choice is that hibernate makes one single query to retrieve the entity and its collections and only when you choose to use this graph  like this   Entity configuration   Entity  NamedEntityGraph name    graph myEntity addresesAndPersons    attributeNodes          NamedAttributeNode value    addreses         NamedAttributeNode value    persons       Usage  public MyEntity findNamedGraph Object id  String namedGraph            EntityGraph lt MyEntity gt  graph   em getEntityGraph namedGraph            Map lt String  Object gt  properties   new HashMap lt  gt             properties put  javax persistence loadgraph   graph            return em find MyEntity class  id  properties

User · Answer

You can traverse over the Getters of the Hibernate object in the same transaction to assure all lazy child objects are fetched eagerly with the following generic helper class      HibernateUtil initializeObject myObject   my app model      package my app util   import java lang reflect InvocationTargetException  import java lang reflect Method  import java util HashSet  import java util Set   import org aspectj org eclipse jdt core dom Modifier  import org hibernate Hibernate   public class HibernateUtil    public static byte   hibernateCollectionPackage    org hibernate collection  getBytes     public static void initializeObject  Object o  String insidePackageName         Set lt Object gt  seenObjects   new HashSet lt Object gt         initializeObject  o  seenObjects  insidePackageName getBytes          seenObjects   null     private static void initializeObject  Object o  Set lt Object gt  seenObjects  byte   insidePackageName          seenObjects add  o         Method   methods   o getClass   getMethods        for   Method method   methods              String methodName   method getName                check Getters exclusively         if   methodName length    lt  3      get  equals  methodName substring  0  3                   continue              Getters without parameters         if   method getParameterTypes   length  gt  0               continue           int modifiers   method getModifiers                Getters that are public         if    Modifier isPublic  modifiers                 continue              but not static         if   Modifier isStatic  modifiers                 continue           try                   Check result of the Getter             Object r   method invoke  o                 if   r    null                   continue                  prevent cycles             if   seenObjects contains  r                     continue                  ignore simple types  arrays und anonymous classes             if    isIgnoredType  r getClass      amp  amp   r getClass   isPrimitive    amp  amp   r getClass   isArray    amp  amp   r getClass   isAnonymousClass                           ignore classes out of the given package and out of the hibernate collection                    package                 if    isClassInPackage  r getClass    insidePackageName    amp  amp   isClassInPackage  r getClass    hibernateCollectionPackage                           continue                                        initialize child object                 Hibernate initialize  r                        traverse over the child object                 initializeObject  r  seenObjects  insidePackageName                             catch   InvocationTargetException e                 e printStackTrace                return            catch   IllegalArgumentException e                 e printStackTrace                return            catch   IllegalAccessException e                 e printStackTrace                return                      private static final Set lt Class lt   gt  gt  IGNORED TYPES   getIgnoredTypes     private static boolean isIgnoredType  Class lt   gt  clazz         return IGNORED TYPES contains  clazz       private static Set lt Class lt   gt  gt  getIgnoredTypes         Set lt Class lt   gt  gt  ret   new HashSet lt Class lt   gt  gt         ret add  Boolean class        ret add  Character class        ret add  Byte class        ret add  Short class        ret add  Integer class        ret add  Long class        ret add  Float class        ret add  Double class        ret add  Void class        ret add  String class        ret add  Class class        ret add  Package class        return ret     private static Boolean isClassInPackage  Class lt   gt  clazz  byte   insidePackageName          Package p   clazz getPackage        if   p    null           return null       byte   packageName   p getName   getBytes         int lenP   packageName length      int lenI   insidePackageName length       if   lenP  lt  lenI           return false       for   int i   0  i  lt  lenI  i               if   packageName i     insidePackageName i                return false             return true

User · Answer

Not the best solution  but here is what I got   1  Annotate getter you want to initialize with this annotation     Retention RetentionPolicy RUNTIME  public  interface Lazy        2  Use this method  can be put in a generic class  or you can change T with Object class  on a object after you read it from database       public  lt T gt  void forceLoadLazyCollections T entity         Session session   getSession   openSession        Transaction tx   null      try            tx   session beginTransaction            session refresh entity           if  entity    null                throw new RuntimeException  Entity is null                       for  Method m   entityClass getMethods                   Lazy annotation   m getAnnotation Lazy class               if  annotation    null                    m setAccessible true                   logger debug   method invoke obj  arg1  arg2          field   m getName                     try                       Hibernate initialize m invoke entity                                      catch  Exception e                        logger warn  initialization exception   e                                                        finally           session close

User · Answer

With Hibernate 4 1 6 a new feature is introduced to handle those lazy association problems  When you enable hibernate enable lazy load no trans property in hibernate properties or in hibernate cfg xml  you will have no LazyInitializationException any more    For More refer   https   stackoverflow com a 11913404 286588

User · Answer

When having to fetch multiple collections  you need to    JOIN FETCH one collection Use the Hibernate initialize for the remaining collections    So  in your case  you need a first JPQL query like this one   MyEntity entity   session createQuery  select e from MyEntity e join fetch e addreses where e id     id   MyEntity class   setParameter  id   entityId   getSingleResult     Hibernate initialize entity persons     This way  you can achieve your goal with 2 SQL queries and avoid a Cartesian Product

[java] Hibernate: best practice to pull all lazy collections

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