How to fix org.hibernate.LazyInitializationException - could not initialize proxy - no Session

If you using Spring mark the class as @Transactional, then Spring will handle session management.

@Transactional
public class MyClass {
    ...
}

By using @Transactional, many important aspects such as transaction propagation are handled automatically. In this case if another transactional method is called the method will have the option of joining the ongoing transaction avoiding the "no session" exception.

WARNING If you do use @Transactional, please be aware of the resulting behavior. See this article for common pitfalls. For example, updates to entities are persisted even if you don't explicitly call save

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You can try to set

<property name="hibernate.enable_lazy_load_no_trans">true</property>

in hibernate.cfg.xml or persistence.xml

The problem to keep in mind with this property are well explained here

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What is wrong here is that your session management configuration is set to close session when you commit transaction. Check if you have something like:

<property name="current_session_context_class">thread</property>

in your configuration.

In order to overcome this problem you could change the configuration of session factory or open another session and only than ask for those lazy loaded objects. But what I would suggest here is to initialize this lazy collection in getModelByModelGroup itself and call:

Hibernate.initialize(subProcessModel.getElement());

when you are still in active session.

And one last thing. A friendly advice. You have something like this in your method:

for (Model m : modelList) {
    if (m.getModelType().getId() == 3) {
        model = m;
        break;
    }
}

Please insted of this code just filter those models with type id equal to 3 in the query statement just couple of lines above.

Some more reading:

session factory configuration

problem with closed session

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The best way to handle the LazyInitializationException is to use the JOIN FETCH directive:

Query query = session.createQuery("""
    select m
    from Model m
    join fetch m.modelType
    where modelGroup.id = :modelGroupId
    """
);

Anyway, DO NOT use the following Anti-Patterns as suggested by some of the answers:

Open Session in View

hibernate.enable_lazy_load_no_trans

Sometimes, a DTO projection is a better choice than fetching entities, and this way, you won't get any LazyInitializationException.

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if you use spring data jpa , spring boot you can add this line in application.properties

spring.jpa.properties.hibernate.enable_lazy_load_no_trans=true

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I was getting the same error for a one to many relationships for below annotation.

@OneToMany(mappedBy="department", cascade = CascadeType.ALL)

Changed as below after adding fetch=FetchType.EAGER, it worked for me.

@OneToMany(mappedBy="department", cascade = CascadeType.ALL, fetch=FetchType.EAGER)

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This exception because of when you call session.getEntityById(), the session will be closed. So you need to re-attach the entity to the session. Or Easy solution is just configure default-lazy="false" to your entity.hbm.xml or if you are using annotations just add @Proxy(lazy=false) to your entity class.

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I encountered the same issue. I think another way to fix this is that you can change the query to join fetch your Element from Model as follows:

Query query = session.createQuery("from Model m join fetch m.element where modelGroup.id = :modelGroupId")

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This means that the object which you are trying to access is not loaded, so write a query that makes a join fetch of the object which you are trying to access.

Eg:

If you are trying to get ObjectB from ObjectA where ObjectB is a foreign key in ObjectA.

Query :

SELECT objA FROM ObjectA obj JOIN FETCH obj.objectB objB

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Faced the same Exception in different use case.

https://i.stack.imgur.com/NuOKs.png

Use Case : Try to read data from DB with DTO projection.

Solution: Use get method instead of load.

Generic Operation

public class HibernateTemplate {
public static Object loadObject(Class<?> cls, Serializable s) {
    Object o = null;
    Transaction tx = null;
    try {
        Session session = HibernateUtil.getSessionFactory().openSession();
        tx = session.beginTransaction();
        o = session.load(cls, s); /*change load to get*/
        tx.commit();
        session.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
    return o;
}

}

Persistence Class

public class Customer {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "Id")
private int customerId;

@Column(name = "Name")
private String customerName;

@Column(name = "City")
private String city;

//constructors , setters and getters

}

CustomerDAO interface

public interface CustomerDAO 
     {
   public CustomerTO getCustomerById(int cid);
     }

Entity Transfer Object Class

public class CustomerTO {

private int customerId;

private String customerName;

private String city;

//constructors , setters and getters

}

Factory Class

public class DAOFactory {

static CustomerDAO customerDAO;
static {
    customerDAO = new HibernateCustomerDAO();
}

public static CustomerDAO getCustomerDAO() {
    return customerDAO;
}

}

Entity specific DAO

public class HibernateCustomerDAO implements CustomerDAO {

@Override
public CustomerTO getCustomerById(int cid) {
    Customer cust = (Customer) HibernateTemplate.loadObject(Customer.class, cid);
    CustomerTO cto = new CustomerTO(cust.getCustomerId(), cust.getCustomerName(), cust.getCity());
    return cto;
}

}

Retrieving data: Test Class

CustomerDAO cdao = DAOFactory.getCustomerDAO();
CustomerTO c1 = cdao.getCustomerById(2);
System.out.println("CustomerName -> " + c1.getCustomerName() + " ,CustomerCity -> " + c1.getCity());

Present Data

https://i.stack.imgur.com/1afXX.png

Query and output generated by Hibernate System

Hibernate: select customer0_.Id as Id1_0_0_, customer0_.City as City2_0_0_, customer0_.Name as Name3_0_0_ from CustomerLab31 customer0_ where customer0_.Id=?

CustomerName -> Cody ,CustomerCity -> LA

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There are several good answers here that handle this error in a broad scope. I ran into a specific situation with Spring Security which had a quick, although probably not optimal, fix.

During user authorization (immediately after logging in and passing authentication) I was testing a user entity for a specific authority in a custom class that extends SimpleUrlAuthenticationSuccessHandler.

My user entity implements UserDetails and has a Set of lazy loaded Roles which threw the "org.hibernate.LazyInitializationException - could not initialize proxy - no Session" exception. Changing that Set from "fetch=FetchType.LAZY" to "fetch=FetchType.EAGER" fixed this for me.

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This means you are using JPA or hibernate in your code and performing modifying operation on DB without making the business logic transaction. So simple solution for this is mark your piece of code @Transactional

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If you are using JPQL, use JOIN FETCH is the easiest way: http://www.objectdb.com/java/jpa/query/jpql/from#LEFT_OUTER_INNER_JOIN_FETCH_

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If you are using Grail's Framework, it's simple to resolve lazy initialization exception by using Lazy keyword on specific field in Domain Class.

For-example:

class Book {
    static belongsTo = [author: Author]
    static mapping = {
        author lazy: false
    }
}

Find further information here

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In my case a misplaced session.clear() was causing this problem.

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In Spring Application Just Add

@Transactional(readOnly = true)

on your Function.

Remind that import spring Transactional annotation import org.springframework.transaction.annotation.Transactional;

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Use @NamedEntityGraph. Eagar fetch will deteriorate the performance. Refer https://thorben-janssen.com/lazyinitializationexception/ for in-depth explanation.

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This happened to me when I was already using @Transactional(value=...) and was using multiple transaction managers.

My forms were sending back data that already had @JsonIgnore on them, so the data being sent back from forms was incomplete.

Originally I used the anti pattern solution, but found it was incredibly slow. I disabled this by setting it to false.

spring.jpa.properties.hibernate.enable_lazy_load_no_trans=false

The fix was to ensure that any objects that had lazy-loaded data that weren't loading were retrieved from the database first.

Optional<Object> objectDBOpt = objectRepository.findById(object.getId());

if (objectDBOpt.isEmpty()) {
    // Throw error
} else {
    Object objectFromDB = objectDBOpt.get();
}

In short, if you've tried all of the other answers, just make sure you look back to check you're loading from the database first if you haven't provided all the @JsonIgnore properties and are using them in your database query.

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All answers about adding JOIN FETCH (or left join fetch) are correct, I want only to add this: if you have converter be sure the getAsObject sub uses a "find" than includes in the sql the Join Fetch too. I lost much time to fix a similar problem, and the problem was in the converter.

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springBootVersion = '2.6.7'

hibernate = 5.6.8.Final'

For me i get the error in:

MyEntity myEntity = myEntityRepository.getById(id);

I change to this:

MyEntity myEntity = myEntityRepository.findById(id).orElse(null);

and i add @ManyToOne(fetch = FetchType.EAGER) in entity

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you could also solved it by adding lazy=false into into your *.hbm.xml file or you can init your object in Hibernate.init(Object) when you get object from db

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uses session.get(*.class, id); but do not load function

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Do the following changes in servlet-context.xml

    <beans:property name="hibernateProperties">
        <beans:props>

            <beans:prop key="hibernate.enable_lazy_load_no_trans">true</beans:prop>

        </beans:props>
    </beans:property>

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