Flutter: Realtime database, append data under specific UID

Question

I'm trying to add a grid on every click to real-time database. However, when a new value is added, although its key is different, still database replaces the old index with new one.

To summarise, this is my intended structure:

User.UID
|
|___ 0 -> cross
|
|___ 1 -> tick
|
|___ 2 -> cross
|
|___ 3 -> tick

But I'm getting:

User.UID
|
|___ 1 -> tick

i.e: Old index 0 is replaced with new index 1.

My code is:

playGame(int index, final databaseReference) {
    if (this.gameState[index] == "empty") {
      setState(() {
        if (this.isCross) {
          this.gameState[index] = "cross";
        } else {
          this.gameState[index] = "circle";
        }
        this.isCross = !this.isCross;
        this.checkWin();
      });

      databaseReference
          .child(authUser.currentUser.uid)
          .set({index.toString(): gameState[index]});
    }

Grid:

Container(
                margin: EdgeInsets.all(15),
                height: MediaQuery.of(context).size.height / 2,
                color: Colors.white12,
                child: GridView.builder(
                  padding: EdgeInsets.only(top: 30),
                  gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
                      crossAxisCount: 3,
                      childAspectRatio: 1.0,
                      crossAxisSpacing: 10.0,
                      mainAxisSpacing: 10.0),
                  itemCount: 9,
                  itemBuilder: (context, i) => SizedBox(
                    child: MaterialButton(
                      onPressed: () {
                        this.playGame(i, databaseReference);
                      },
                      child: Image(
                        image: this.getImage(this.gameState[i]),
                      ),
                    ),
                  ),
                ),
              ),

Can anyone please help how can I fix this?

Answer 1

When you call set(...) on a location, it sets the values you pass to that location, overwriting any existing value(s) at the location.

If you want to only update specific keys in the location, use the update(...) method. So in your case that'd me:

databaseReference
  .child(authUser.currentUser.uid)
  .update({index.toString(): gameState[index]});