LazyInitializationException in selectManyCheckbox on @ManyToMany(fetch=LAZY)

Question

What is the best way to handle multiple chackboxes when you nead to fill a JPA M:N relation ... for example I have an JPA entity Hardware and the entity Connectivity.

Answer 1

You need to fetch it while inside a transaction (thus, inside the service method), and not while outside a transaction (thus, inside e.g. JSF managed bean init/action method), that would thus throw a LazyInitializationException.

So, your attempt

hardware.getConnectivities().size();

has to take place inside a transaction. Create if necessary a new service method for the purpose whereby you pass the entity which was obtained before in another transaction.

hardwareService.fetchConnectivities(hardware);

public void fetchConnectivities(Hardware hardware) {
    hardware.setConnectivities(em.merge(hardware).getConnectivities()); // Becomes managed.
    hardware.getConnectivities().size(); // Triggers lazy initialization.
}

An alternative would be to create a DTO for the purpose which has it eagerly fetched.

And then to save the selected items, make sure that you explicitly specify the selection component's collectionType attribute to a standard Java type rather than letting it autodiscover a JPA impl specific lazy loaded type such as org.hibernate.collection.internal.PersistentSet in your specific case. JSF needs it in order to instantiate the collection before filling it with the selected items.

See also org.hibernate.LazyInitializationException at com.sun.faces.renderkit.html_basic.MenuRenderer.convertSelectManyValuesForModel.