fix(datastore): emit observeQuery snapshot when model create mutation results in an updated model

[Jordan-Nelson]

Issue #, if available: #3649

Description of changes:

• When event type is EventType.create and the model already exists in the list, evaluate if the model has changed

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[Jordan-Nelson]

note: I refactored this and added comments to make it easier to understand but this code block is the only logic change. When the event type is EventType.create and the item value has changed (currentItem != newItem) the item in the list is updated with the new value. Previously this was ignored. This is problem when the model create response from App Sync contains an updated model, which is the case when using a custom resolver.

[Equartey]

question: is currentItem != newItem a sufficient comparison, like is it a deep equals?

[Jordan-Nelson]

Yes, item is of type Model and we override the equality operator on models. For example, a typical Blog model would look like:

  @override
  bool operator ==(Object other) {
    if (identical(other, this)) return true;
    return other is Blog &&
        id == other.id &&
        _name == other._name &&
        DeepCollectionEquality().equals(_posts, other._posts);
  }