如何使用 flutter 从 Firestore 获取子集合？

Question

I wanna fetch the data inside the Guests like guestName. The code below I used it to fetch collection and it worked, but I have no idea how to fetch subcollection. I been trying but it's not working.

    body: CustomScrollView(
slivers: [
SliverPersistentHeader(pinned: true, delegate: SearchBoxDelegate()),
StreamBuilder<QuerySnapshot>(

//I used this to fetch collection but it doesn't work with subcollection
stream: Firestore.instance
.collection("Guests")
.orderBy("Date", descending: true).snapshots(),
builder: (context, dataSnapshot) {
return !dataSnapshot.hasData
? SliverToBoxAdapter(
    child: Center(
      child: circularProgress(),
    ),
  )
: SliverStaggeredGrid.countBuilder(
    crossAxisCount: 1,
    staggeredTileBuilder: (c) => StaggeredTile.fit(1),
    itemBuilder: (context, index) {
      ItemModel model = ItemModel.fromJson(
          dataSnapshot.data.documents[index].data);
      return sourceInfo(model, context);
    },
    itemCount: dataSnapshot.data.documents.length,
  );
},
),
],
),

Container(
child: Row(
  mainAxisSize: MainAxisSize.max,
  children: [
    Expanded(
      child: Text(
      // this guestName i wanna fetch
        model.guestName,
        style: TextStyle(
            color: Colors.black, fontSize: 14.0),
      ),
    ),
  ],
),
),

Answer 1

To get a CollectionReference for a subcollection, you first need to have a DocumentReference object to its parent document, and then you can call collection() on that.

In your builder you have dataSnapshot.data.documents[index] , which gives you a DocumentSnapshot object , from which you can get a DocumentReference by calling reference on it.

So combined that'd be something like this in your builder:

dataSnapshot.data.documents[index].reference.collection("Guests")

I recommend always keeping the reference documentation handy that I linked above, as it's the easiest way to find this type of API path.