Firestore - Deep Queries

问题

I have a Firestore that contains a collection (Items) that contains subcollections (called "things"). When I get my Items collection I get all of the child documents but none of the child collections. I would like to do a deep retrieval, one object called Items that contains the sub-collections.

I understand this is not possible out of the box, but I am struggling to write the code myself to do this.

Can anyone help?

constructor(public afs: AngularFirestore) {
//this.items = this.afs.collection('Items').valueChanges();
this.itemsCollection = this.afs.collection('Items', ref => ref.orderBy('year', 'asc'));

this.items = this.itemsCollection.snapshotChanges().map(changes => {
  return changes.map(a => {
    const data = a.payload.doc.data() as Item;
    data.id = a.payload.doc.id;
    return data;
  });
});
}

getItems() {
 return this.items;
}

回答1:

Yes, you can execute the code below to get what you want to. Basically this code gets for each item its things subcollection:

  getItems(): Promise<any> {
    return this.db.collection('items').get().then(
      items => {
        return this.getThingsForItems(items);
      });
  }

  getThingsForItems(items): Promise<any> {
    return Promise.all(items.docs.map(async (element) => {
      var things = []
      const response = await this.db.collection('items')
                            .doc(element.id).collection('things').get();

      response.forEach(subcollectionItem => {
        things.push(subcollectionItem.data());
      });

      return { Item: element.data(), Things: things }
    }));
  }

The getItems method will return a promisse that contains your items with its things subcollection.

Something like that:

Keep in mind that this query can become a slow-running query since it is making a get for each document of the items collection. So you might should consider denormalize your database or transform the things subcolletion in an array of the items documents (in this case you should be aware that a document has a max size of 1MB, so do not consider this option if you are array can become too big).

来源：https://stackoverflow.com/questions/48084825/firestore-deep-queries