Import save results from a “sandbox editor”

“Sandbox editing” is a common Breeze pattern for isolating user changes from the “mainstream” entities.

In this pattern, you create two EntityManagers. You maintain a masterEm which has only the pristine, last-saved state of your application entities. You create a second editEm where you allow users to make changes.

You only make and save changes in that separate editEm. You import the entities-to-edit from masterEm into the editEm, make changes there, save them, and (if the save is successful), you export the saved entities from editEm and import them back into masterEm.

It sounds more complicated than it is. It works out to a small amount of Breeze code (as we will see) and you get nice isolation of change activity.

Trouble arises when you delete an entity in editEm. After save, that entity is “Detached” in the editEm but it’s still in an “Unchanged” state back in the masterEm. How do you communicate the fact that the entity is deleted and remove it from masterEm?

You cannot simple import the saved entities into masterEm. This will not work properly

    // DON'T DO THIS
    masterEm.importEntities(editEm.exportEntities(entities, false));
} If you try, you'll discover that things went very wrong for any of the `saveResult` entities that were deleted. Such entities are in a "Detached" state ... they don't belong to *any* `EntityManager`. The `exportEntities` method should throw an error.

It will throw an error as of v.1.5.4. There was a bug prior to that version and it seemed that Breeze supported export/import of “Detached” entities. That was a bug.

Fortunately, you can write a utility function that “does the right thing”: it imports changed entities and detaches deleted entities.

Here is an example that you will also find in DocCode:exportImportTests.js with a corresponding unit test.

function updateMasterWithSaveResult(masterEm, sourceEm, saveResult) {
  var imports = [];
  var deletes = [];
  saveResult.entities.forEach(function(entity) {
    if (entity.entityAspect.entityState.isDetached()) {
    } else {
  var exported = sourceEm.exportEntities(imports, {
    includeMetadata: false,
    asString: false // as JSON

  deletes.forEach(function(detached) {
    var entity = masterEm.getEntityByKey(detached.entityAspect.getKey());
    entity && entity.entityAspect.setDetached();

You could call it in the save success promise callback like this:

return editEm.saveChanges()
           .then(function(saveResult) {
               updateMasterWithSaveResult(masterEm, editEm, saveResult);