[rfcs] - knowing when records are loaded or not

[fivetanley]

When people are trying to check for contains/etc. See if the relationship has been loaded without asking the server for the records. There is currently no API for this.

An example: has the post loaded its comments? if not I may want to make a different kind of query

What are the comment IDs? I may have not yet loaded the comments but I want to know their IDs without telling the server to load them.

We would like contributors to use this issue for use cases.

[aaronbhansen]

We have a few situations we need to filter or check a relation based on the id, but don't need the entire relation loaded. One example of how we are using this is in the gist. This isn't related as much as to knowing if the records are loaded, but more towards the second part of your issue, knowing the id without requesting the full data from the server.

https://gist.github.com/aaronbhansen/078c14ac65df6985bcd4

We might change our workflow depending on if we knew records were loaded or not, but since there hasn't been an easy way to do this so far, I don't have any code examples for your first half of the issue.

[sandstrom]

This is copied from another issue (#2271), on determining relationship presence (somewhat related).

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Sometimes it's useful to determine if a relationship is present without querying the server. child.get('mother') will query the server if the mother isn't present.

This private API works without querying the server: !!child._relationships.mother.inverseRecord.

On knowledge of associated records
Mostly, only the 1-side in N-1 and 1-1 relationships will know whether it's associated with another record (given how foreign keys are located). The N-side won't know without querying the server.

Ways to provide this

1. child.isPresent('mother') return true/false
2. child.get('mother', { local: true }) return the record if it exists in store, otherwise null
3. child.count('mother') could return without querying the server for 1-side, and could trigger a server request for the N-side. It's main usage would obviously be remote counting, but that way the API addition would be useful for more than probing for existence.
4. eachRelationship could be amended to provide info on relationship presence (similar to the current, private, API quoted above).

I think I like (3) the most, but depends on whether others think that's a useful addition.

[igorT]

emberjs/rfcs#57 is aiming to address this

[pangratz]

I think this issue can be closed since an initial implementation of references has been merged into master. Having the ds-references feature enabled, it can be checked if there is data for a relationship via model.belongsTo("family").value() !== null and model.hasMany("children").value() !== null.

[fivetanley]

@pangratz thank you!