Deprecation Guide for Deprecate Promise Many Array Behaviors
This deprecation deprecates accessing values on the asynchronous proxy in favor of first "resolving" or "awaiting" the promise to retrieve a synchronous value.
Template iteration of the asynchronous value will still work and not trigger the deprecation, but all JS access should be avoided and HBS access for anything but {{#each}} should also be refactored.
Recommended approaches include using the addon ember-promise-helpers, using Ember's resource pattern (including potentially the addon ember-data-resources), resolving the value in routes/provider components, or using the references API.
An example of using the hasMany reference API:
// get the synchronous "ManyArray" value for the asynchronous "friends" relationship.
// note, this will return `null` if the relationship has not been loaded yet
const value = person.hasMany('friends').value();
// to get just the list of related IDs
const ids = person.hasMany('friends').ids();
References participate in autotracking and getters/cached getters etc. which consume them will recompute if the value changes.