feat(firestore): Support Firestore Collection Group Queries

[jamesdaniels]

Checklist

• Issue number for this PR: #nnn (required)
• Docs included?: (yes/no; required for all API/functional changes)
• Test units included?: (yes/no; required)
• In a clean directory, yarn install, yarn test run successfully? (yes/no; required)

Description

Code sample

constructor(private afs: AngularFirestore) { }

ngOnInit() {
  ...
  // Get all the user's comments, no matter how deeply nested
  this.comments$ = afs.collectionGroup('Comments', ref => ref.where('user', '==', userId))
                      .valueChanges({ idField });
}

[jamesdaniels]

FYI this has been released for testing on @next as of 5.2.0-beta.3

[jamesdaniels]

Adding @davideast for review, alternatively @jhuleatt this could be a good one for a pair review. LMK

[jhuleatt]

I found this a bit tough to interpret on the first pass.

Maybe something like "... similar to AngularFirestoreCollection. The main difference is that AngularFirestoreCollectionGroup has no data operation methods such as add because it doesn't have a unique(?concrete?) reference.

[jamesdaniels]

I like concrete.

[jhuleatt]

worth throwing a link to the release notes into this error? https://firebase.google.com/support/release-notes/js#version_600_-_may_7_2019

[jamesdaniels]

Eh, probably not. I imagine we'll be talking about so few users over the next couple months & more advanced ones at that.

[jamesdaniels]

Thanks for reviewing @jhuleatt

[valterh4ck3r]

So awesome <3

I'm needing this, thank you for your feature request @jamesdaniels and @jhuleatt.