How do I get documentid of a firestore document in flutter?

Question

I have tried the following but it returns a random string which is not present in the firestore.

I did manage to get documentid of parent collection using a Query Snapshot

DocumentReference doc_ref=Firestore.instance.collection("board").document(doc_id).collection("Dates").document();

                    var doc_id2=doc_ref.documentID;

More Code: I am getting an error in trying to access the document id. I have tried to use await but its giving an error.

 Widget build(BuildContext context) {
        return Scaffold(
          appBar: new AppBar(
            title: new Text(
              "National Security Agency",
              style: TextStyle(
                  color: Colors.black,
                  fontWeight: FontWeight.normal,
                  fontSize: 24.0),
            ),
            backgroundColor: Colors.redAccent,
            centerTitle: true,
            actions: <Widget>[
              new DropdownButton<String>(
                items: <String>['Sign Out'].map((String value) {
                  return new DropdownMenuItem<String>(
                    value: value,
                    child: new Text(value),
                  );
                }).toList(),
                onChanged: (_) => logout(),
              )
            ],
          ),
          floatingActionButton: FloatingActionButton(
            onPressed: () {
    
            },
            child: Icon(Icons.search),
          ),
    
          body: StreamBuilder (
              stream: cloudfirestoredb,
    
    
                  builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
                    if (!snapshot.hasData) return new Text('Loading...');
    
                    return new ListView(
                      children: snapshot.data.documents.map((document) {
    
    
                        var doc_id=document.documentID;
                        var now= new DateTime.now();
                        var formatter=new DateFormat('MM/dd/yyyy');
                        String formatdate = formatter.format(now);
                        var date_to_be_added=[formatdate];
    
                        DocumentReference doc_ref=Firestore.instance.collection("board").document(doc_id).collection("Dates").document();
    
                       var doc_id5= await get_data(doc_ref);
    
    
                        print(doc_id);
                        
    
    
                        Firestore.instance.collection("board").document(doc_id).collection("Dates").document(doc_id5).updateData({"Date":FieldValue.arrayUnion(date_to_be_added)});
                        return cardtemplate(document['Name'], document['Nationality'], doc_id);
    
                        }).toList(),
                    );
                  },
           ),
              );
      }

Answer 1

You have to retrieve that document for its id.

Try this

DocumentReference doc_ref=Firestore.instance.collection("board").document(doc_id).collection("Dates").document();

DocumentSnapshot docSnap = await doc_ref.get();
var doc_id2 = docSnap.reference.documentID;

Make sure you use this in a function marked as async since the code uses await.

Edit : To answer your question in the comments

Future<String> get_data(DocumentReference doc_ref) async { 
  DocumentSnapshot docSnap = await doc_ref.get(); 
  var doc_id2 = docSnap.reference.documentID; 
  return doc_id2; 
}

//To retrieve the string
String documentID = await get_data();

Edit 2 :

Just add async to the map function.

snapshot.data.documents.map((document) async {
  var doc_id=document.documentID;
  var now= new DateTime.now();
  var formatter=new DateFormat('MM/dd/yyyy');
  String formatdate = formatter.format(now);
  var date_to_be_added=[formatdate];

  DocumentReference doc_ref=Firestore.instance.collection("board").document(doc_id).collection("Dates").document();

  var doc_id5= await get_data(doc_ref);

  print(doc_id);

  Firestore.instance.collection("board").document(doc_id).collection("Dates").document(doc_id5).updateData({"Date":FieldValue.arrayUnion(date_to_be_added)});
  return cardtemplate(document['Name'], document['Nationality'], doc_id);
}).toList(),

let me know if this works