Suppose you have two models:
Post, Comment Where Post hasMany Comments and Comment belongsTo Post
It should be possible to commit a transaction where both a new Post and Comment are created and related to each other.
Currently this fails as the Comment will attempt to save without an ID.
This could be accomplished by adapter logic to defer portions of the commit until the parent record is saved, or by adding support for saving records in an embedded manner.
Shouldn't it be an ember-data issue?
This is planned for ember-data, but will likely still require adapter specific logic, and an adapter implementation is currently recommended for this functionality.
There is not a generic solution to solve this. I think that until a proposal is given by the ember-data team, the best option is extend the adapter and build that customized feature.