Relationships

EmberFire can handle relationships in several different ways:

1. hasMany will query for matching records in a root collection
2. hasMany with the query: ref => ref allows you to alter to assumed query
3. hasMany with the subcollection: true option will query records in a Firestore subcollection
4. hasMany with the subcollection: true, query: ref => ref similarly allows you tack on a subcollection query
5. hasMany with the embedded: true option will embed the records in the Firestore document
6. belongsTo will query for matching records in a root collection
7. belongsTo with the query: ref => ref option allows you to modify the assumed query