Start RFC to deprecate the use of Ember Evented in Ember Data

text/1234-deprecated-ember-evented-in-ember-data.md

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+- Start Date: 2018-05-01
+- RFC PR: (leave this empty)
+- Ember Issue: (leave this empty)
+
+# Deprecate Usage of Ember Evented in Ember Data
+
+## Summary
+
+`Ember.Evented` functionality on `DS.Model`, `DS.ManyArray`,
+`DS.Errors`, `DS.RecordArray`, and `DS.PromiseManyArray` will be
+deprecated and eventually removed in a future release. This includes
+the following methods from the
+[Ember.Evented](https://www.emberjs.com/api/ember/2.15/classes/Ember.Evented/methods/on?anchor=off)
+class: `has`, `off`, `on`, `one`, and `trigger`. Additionally the
+following lifecycle methods on `DS.Model` will also be deprecated:
+`becameError`, `becameInvalid`, `didCreate`, `didDelete`, `didLoad`,
+`didUpdate`, `ready`, `rolledBack`.
+
+## Motivation
+
+The use of `Ember.Evented` is mostly a legacy from the pre 1.0 days of
+Ember Data when events were a core part of the Ember Data programming
+model. Today there are better ways to do everything that once needed
+events. Removing the usage of the `Ember.Evented` mixin will make it
+easier for Ember Data to eventually transition to using native ES2015
+JavaScript classes and will reduce the surface area of APIs that Ember
+Data must support in the long term.
+
+## Detailed design
+
+`Ember.Evented` mixin will be scheduled to be removed from the
+following classes after the next LTS release: `DS.Model`,
+`DS.ManyArray`, `DS.Errors`, `DS.RecordArray`, and
+`DS.PromiseManyArray`.
+
+The `has`, `off`, `on`, `one`, and `trigger` methods will be trigger a
+deprecation warning when called and will be completly removed in Ember
+Data 3.5 (the release following the 3.4 LTS release).
+
+A special deprecation will be logged when users of a
+`DS.adapterPopulatedRecordArray` attempt to listen to the `didLoad`
+event. This depecations will prompt users to use a computed property
+instead of the `didLoad` event.
+
+
+`DS.Model` will also recieve deprecation warnings when a model is
+defined with the following methods: `becameError`, `becameInvalid`,
+`didCreate`, `didDelete`, `didLoad`, `didUpdate`, `ready`,
+`rolledBack`.
+
+When a model is instantiated for the first time with any of these
+methods a deprecation warning will be logged notifiying the user that
+this method will be deprecated and the user should use an computed or
+overide the model's init method instead.
+
+## How we teach this
+
+Today we do not teach the use of any of the Ember Data lifecycle
+events in the guides. They are referenced in the API docs but they
+will be updated to mark the APIs as deprecated and show alternative
+examples of how to achieve the same functionality using a non event
+pattern.
+
+## Drawbacks
+
+The drawback to making this change is existing code that takes
+advantage of the Ember Data lifecycle events will need to be updated
+to use a different pattern.
+
+## Alternatives
+
+We could leave the `Ember.Evented` mixin on all of the Ember Data
+objects that currently support it and continue to support this
+interface for the foreseeable future. However, Ember Data itself
+doesn't require these events internally. There is only one place in
+the `DS.Error` code that takes advantage of the `Ember.Evented` system
+and that code can be easilly re-written to avoid `Ember.Evented` APIs.
+
+## Unresolved questions
+
+None