JSONSerializer.serializeHasMany() behaves differently depending on the way the record has been added to the store

[sebweaver]

Here is a JSBin highlighting the two behaviors: http://emberjs.jsbin.com/rocano/8/edit?js,console,output

On the first case (post added by createRecord) the json is:

{ comments: [] }

On the 2nd case (post added by push) the json is:

{ comments: undefined }

Shouldn't be the same (i.e. the 1st one)? Or is it by design to have undefined relationships on the 2nd one?

[wecc]

Thanks for reporting!

The bug is here: https://github.com/emberjs/data/blob/master/packages/ember-data/lib/serializers/json-serializer.js#L1127

snapshot.hasMany() returns undefined for "unknown" relationships (docs). That is, you've pushed the record into the store, but the relationship is missing. ED cannot know if there's additional data on the server or not, that's why there's a "unknown" state of a relationship. We wouldn't want to serialize unknown relationships to [] because that might overwrite server state.

When you do store.createRecord() we consider the record as new and client-side and because of that all the relationships are known (which means snapshot.hasMany() returns an empty array instead of undefined)

The JSONAPISerializer handles this correctly, see https://github.com/emberjs/data/blob/master/packages/ember-data/lib/serializers/json-api-serializer.js#L428-L429

[sebweaver]

First of all thank you for your quick and detailed answer. I've noticed the difference between the two serializers, but I didn't know whether it was on purpose or not. With your explanation it's now clear.

Thanks

[wecc]

I would still consider this a bug. Unknown relationships should be omitted when serializing records using JSONSerializer (and RESTSerializer).

[sebweaver]

I've created a PR: #3765

[e00dan]

Shouldn't this be closed because of #3765 merged?