firebase - Flutter firestore - Check if document ID already exists

Question

I want to add data into the firestore database if the document ID doesn't already exists. What I've tried so far:

// varuId == the ID that is set to the document when created


var firestore = Firestore.instance;

if (firestore.collection("posts").document().documentID == varuId) {
                      return AlertDialog(
                        content: Text("Object already exist"),
                        actions: <Widget>[
                          FlatButton(
                            child: Text("OK"),
                            onPressed: () {}
                          )
                        ],
                      );
                    } else {
                      Navigator.of(context).pop();
                      //Adds data to the function creating the document
                      crudObj.addData({ 
                        'Vara': this.vara,
                        'Utg?ngsdatum': this.bastFore,
                      }, this.varuId).catchError((e) {
                        print(e);
                      });
                    }

The goal is to check all the documents ID in the database and see in any matches with the "varuId" variable. If it matches, the document won't be created. If it doesn't match, It should create a new document

Answer 1

Waitting for answers