Is a Firestore Query Snaphot in flutter ever null?

Question

In my flutter app I am checking if a document exists based on certain parameters and based on snapshot.hasData build the widget.

However I remember reading somewhere, at least when coding in Kotlin (and I assume should be true with Flutter), that a snapshot can never be null??

If this is the case, how can I check if a document exists or not and use the fact that the document does not exist to build the widget. i know i am using a query snapshot

i have it running as follows:

FutureBuilder(
  future: checkSeller(deal_id_chosen),
  builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot2) {

      if (snapshot2.connectionState ==
          ConnectionState.waiting) {
        return Center(
          child: CircularProgressIndicator(),
        );

      } else if (snapshot2.connectionState == ConnectionState.done) {

        if(snapshot2.data['seller_id'] == null){

          return Text('doesnt exist');
        }

        if(snapshot2.data['seller_id'] == uid_global){
        return Text('seller exists');
}


      } else if (snapshot2.hasError) {
        return Text('no data');
      }
      return CircularProgressIndicator();

  },

),

My Firebase Query a follows (this runs fine but always returns as true, even when a document should not exist)

  Future<QuerySnapshot> checkSeller(deal_id) async{


return await Firestore.instance.collection('Deals').where('deal_id'.isEqualTo:deal_id).where('seller_id',isEqualTo:uid_global).getDocuments();


  }

Can you do such a query, because I was expecting the FutureBuilder to not satisfy the snapshot2.hasData and hence allow me to switch between either building a widget saying that the seller exists or seller doesn't exist in my case.

Answer 1

Not having any results is not an error condition for a query. To check if a query had any results, check if the length of the QuerySnapshot.documents property is greater than 0.