"lazy initialization" allows framework to lazily initialize dependencies, relationship or association lazily from database on need basis.
For example, if you are dealing with User object, which has relationship with Permission object like one user can have multiple permissions, then Hibernate may choose not to initialize the collection which holds all permissions at the time it initialized User object and instead returns a proxy object. At this point, if you close your session and letter tries to access an attribute from Permission object, you will get "org.hibernate.LazyInitializationException: could not initialize proxy - no Session in Hibernate".
hibernate needs to go database to initialize the proxy object, but connection is already closed.
org.hibernate.LazyInitializationException: could not initialize proxy - no Session. this error mainly comes when you have closed the connection and trying to access the proxy object which is no fully initialized.
1) Code tries to access a lazy initialized property or collection and session is not available.
Easy Solution
Use lazy=false in hibernate mapping file.
main disadvantage of this approach can be slow performance. Since dependent objects are loaded at the time of persistent object loading, it will increase loading time. Also since now object is fully initialized, there memory consumption would be very high. This can become more severe if your Collection classes are big list of other objects, which are not always accessed.
Better Solution :
The real problem is that you are trying to access a collection in an object that is detached or associated session is closed. You need to re-attach the object before accessing the collection to the current session. You can either reattach the object by calling session.update(object); Or you can move the code which access proxy object to the line before you close the session.
Hibernate with JPA Annotation
If you are using hibernate with JPA annotations and manually managing your transactions: In your service class there should be a setter for entity manager with @PersistenceContext. change this to @PersistenceContext(type = PersistenceContextType.EXTENDED). Then you can access lazy property in any where. By the way, its worth remember that, Spring EXTENDED persistence context type is for long conversation pattern, not the session-per-request pattern.
4) Application wide Solution
When we want an easy solution and doesn't care anything about performance e.g. for testing or prototyping purpose. In that case you can make following configuration change into your application to avoid this error, but remember the impact eager initialization can cause if this code makes its way to production.
if you are using XML configuration: add default-lazy="false" to your element
if you are using annotation configuration: add @Proxy(lazy=false) to all your entity classes.
Read full article from Dealing with org.hibernate.LazyInitializationException: could not initialize proxy - no Session in Hibernate Java
For example, if you are dealing with User object, which has relationship with Permission object like one user can have multiple permissions, then Hibernate may choose not to initialize the collection which holds all permissions at the time it initialized User object and instead returns a proxy object. At this point, if you close your session and letter tries to access an attribute from Permission object, you will get "org.hibernate.LazyInitializationException: could not initialize proxy - no Session in Hibernate".
hibernate needs to go database to initialize the proxy object, but connection is already closed.
org.hibernate.LazyInitializationException: could not initialize proxy - no Session. this error mainly comes when you have closed the connection and trying to access the proxy object which is no fully initialized.
1) Code tries to access a lazy initialized property or collection and session is not available.
Easy Solution
Use lazy=false in hibernate mapping file.
main disadvantage of this approach can be slow performance. Since dependent objects are loaded at the time of persistent object loading, it will increase loading time. Also since now object is fully initialized, there memory consumption would be very high. This can become more severe if your Collection classes are big list of other objects, which are not always accessed.
Better Solution :
The real problem is that you are trying to access a collection in an object that is detached or associated session is closed. You need to re-attach the object before accessing the collection to the current session. You can either reattach the object by calling session.update(object); Or you can move the code which access proxy object to the line before you close the session.
Hibernate with JPA Annotation
If you are using hibernate with JPA annotations and manually managing your transactions: In your service class there should be a setter for entity manager with @PersistenceContext. change this to @PersistenceContext(type = PersistenceContextType.EXTENDED). Then you can access lazy property in any where. By the way, its worth remember that, Spring EXTENDED persistence context type is for long conversation pattern, not the session-per-request pattern.
4) Application wide Solution
When we want an easy solution and doesn't care anything about performance e.g. for testing or prototyping purpose. In that case you can make following configuration change into your application to avoid this error, but remember the impact eager initialization can cause if this code makes its way to production.
if you are using XML configuration: add default-lazy="false" to your element
if you are using annotation configuration: add @Proxy(lazy=false) to all your entity classes.
Read full article from Dealing with org.hibernate.LazyInitializationException: could not initialize proxy - no Session in Hibernate Java
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