flutter query multiple collections in firestore

Question

I am playing with flutter but I ran into an issue with firestore that I can\'t figure out.

let\'s say I would like to retrieve the purchaser history of a customer and I

Answer 1

Short answer i didn't pay attention to how you use a future

Get the productId from the user table

  Future> getProduceID() async{
    var data = await Firestore.instance.collection('users').document(widget.userId).collection('Products').getDocuments();
    var productId = data.documents;
    return productId;
  }

Then call this using .then() rather than try to apply the returned data to the variable as that is not how a future it works

  var products;
  getProduceID().then((data){
  for(int i = 0; i < s.length; i++) {
    products = Firestore.instance.collection('products')
        .document(data[i]['productID'])
        .snapshots();
    if (products != null) {
      products.forEach((product) {
        print(product.data.values);
      });
    }
  }
});