Flutter - Get array from Firestore with FutureBuilder (using query)

Question

I'm confusing myself terribly here...what is the correct syntax for listing an array from Firestore with FutureBuilder if I need to perform a document (where) query?

Firestore Database Structure:

 - [companies]
   - [doc]

 - [gallery]
   - [doc]
    - [reference] <- (ie, companies/doc)
    - [gallery_images] // List these, but show only images that match where() query

Here is my current code:

Future<List<dynamic>> getGallery() async {
  var firestore = Firestore.instance;

  DocumentReference docRef = firestore.collection('companies').document(widget.docID);

  var ref = firestore.collection('galleries').where('companyRef', isEqualTo: docRef).getDocuments();

  return ref.get().then((datasnapshot) {
        if (datasnapshot.exists) {
        List<dynamic> imageArray = datasnapshot.data['gallery_images'].toList();
          return imageArray;
        } else {
          print("Please just work...");
        }
      },
    );
  }

FutureBuilder(
  future: getGallery(),
  builder: (context, AsyncSnapshot<List<dynamic>> snapshot) {
    if (snapshot.connectionState == ConnectionState.waiting) {
      return Center(
         child: Text("Loading..."),
        );
       } else {
    return GridView.builder(
    gridDelegate: new SliverGridDelegateWithFixedCrossAxisCount(crossAxisCount: 2),
    itemCount: *length*,
    itemBuilder: (BuildContext context, int index) {
       return ViewGalleryItemThumbnail(
         viewGalleryItem: snapshot.data[index],
         ....

Would really appreciate if someone can show me where I'm going wrong!

Answer 1

It's not exactly clear what your Cloud Firestore schema looks like, but this looks more likely to return you the correct list of dynamics. (Note that by adding a generic to the map you could return a list of specifically what you want - eg .map<SomeRealType>((snap) => snap.data['gallery_images']) .)

When you're stuck with FutureBuilder it's sometimes useful to revert temporarily to a stateful widget. Override initState , and call a slightly modified getGallery which doesn't return a value at the end, but assigns it to a member variable inside setState . Plenty of opportunity for print statements that way. Additionally, try to convert any .then s in an async function into a linear series of await s. It makes it easier to read (and your debug prints come out in a linear sensible order).

  Future<List<dynamic>> getGallery() async {
    var firestore = Firestore.instance;

    var docRef = firestore.collection('companies').document(widget.docID);

    var querySnap = await firestore
        .collection('galleries')
        .where('companyRef', isEqualTo: docRef)
        .getDocuments();

    return querySnap.documents
        .map((snap) => snap.data['gallery_images'])
        .toList();
  }