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EmberData | Deprecate Model Reopen

Summary

Deprecates using reopen to alter clases extending @ember-data/model.

Motivation

reopen restricts the ability of EmberData to design better primitives that maintain compatibility with @ember-data/model, and is a footgun that leads to confusing incorrect states for users that utilize it.

Detailed design

The static reopen method on Model will be overwritten to provide a deprecation which once resolved or after the deprecation lifecycle completes will result in reopen throwing an error when used in dev and silently no-oping in production. This deprecation will target 5.0 and not be enabled sooner than 4.1 though it may come available before that.

How we teach this

This is best taught through a deprecation guide. Users using reopen to test multiple configurations in their test suite should instead extend and register a new model each time.

Users using reopen to modify a class immediately after creating it should also refactor to extend instead.

Users using reopen to modify a class dynamically at runtime should refactor to either register new model types or (better) utilize a megamorphic solution such as ember-m3 to achieve their needs.

In all cases, using reopen after a class instance for a record has already been created has always resulted in at least minor and potentially major errors in application state.

Drawbacks

Test suites, including EmberData's own, that make use of reopen are often "order dependent" in order for the test suite to pass, and refactoring them can sometimes be a difficult exercise in determining which tests had modified the class to achieve the model shape needed by another test. In general though the drawbacks here are small given the widespread adoption of class syntax and growing adoption of octane paradigms.

Alternatives

  • Don't deprecate reopen and wait to replace @ember-data/model in it's entirety. This alternative would prevent us from providing custom decorators not extending from computed and limit potential build tools allowing users to optimize existing usage of EmberData.

  • Wait for ember to deprecate reopen. Because we cannot build custom decorators and support reopen without asking for ember to make available to use private APIs I do not think we should wait for Ember here. This RFC does not preclude or force Ember to deprecate reopen more broadly.