Working with Entities in UI

Entities loaded into a view become associated with the view components, such as data containers and DataContext. This association occurs because data containers and DataContext register listeners that respond to changes in the entity attributes. When passing the loaded entities to services for modification and saving, the entity instances should be isolated from the view components. Otherwise, the changes made by the service will directly affect the view state. Additionally, there is a risk of memory leaks if the instances are retained in a cache.

The standard implementation of DataContext provides proper isolation of saved instances while saving entities to DataManager. This is achieved through the use of the io.jmix.core.Copier bean.

You can do the same to isolate entities when sending them from views to custom services. The following example shows how to save an entity by a service:

@ViewComponent
private DataContext dataContext;
@Autowired
private DepartmentService departmentService;
@Autowired
private Copier copier;

private void saveToCustomService(Department entity) {
    Department entityCopy = copier.copy(entity); (1)

    Department savedEntity = departmentService.saveEntity(entityCopy); (2)

    Department ignored = dataContext.merge(savedEntity);(3)
}
1 Make a copy of the entity to separate the instance representing the view state from the one that is being saved.
2 Send the copy to the service.
3 If you want to update the view state by the changes made in the service, merge the returned instance back into DataContext. The result of the merge() operation can be safely ignored in this case.

When using saveDelegate handler to intercept the standard DataContext save procedure, take into account the following differences from a regular method shown above:

  • The SaveContext object already contains copies of entities associated with the view components, so you don’t need to create copies again.

  • The saved entities returned in the resulting Set from the handler are merged into the DataContext automatically, therefore you shouldn’t invoke merge() operation explicitly.
See also the Saving entity by custom service online example that demonstrates how to isolate entities when sending them from a view to a custom service.