android - 嵌套的 Firebase 查询

Question

我正在尝试在另一个 firebase 查询中执行一个 firebase 查询，例如嵌套 for 循环，但外部查询在内部查询开始之前完全运行。我如何做到这一点？我是 android 和 firebase 初学者

外部查询

 private void retrieveMarkerDetails(final String key) {
    databaseReference = mDatabase.getReference();

    databaseReference.child("Parking Lots").child(key).addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            parking_lot_details = dataSnapshot.getValue(Parking_Lot_Details.class);



            Marker marker;

            if (markers.size() != 0) {
                marker = markers.get(key);
                String title = parking_lot_details.getLotName();




                //Calculate Remaining space
                spaceAvailable();

Log.i("可用剩余空间", String.valueOf(parking_lot_details.getAvailableSpace()));

                String snippet = "Available space " + parking_lot_details.getAvailableSpace();

                Log.i("remaining space", String.valueOf(parking_lot_details.getCapacity()));

                // String snippet = "Available space " + parking_lot_details.getCapacity();
                marker.setTitle(title);
                marker.setSnippet("\t" + snippet);
                Log.i("key : ", key);

内部查询这是应该运行的内部查询。

private void spaceAvailable() {

    spaceAvailable = new int[1];


    //Strip email of dots and use it to access requests, since the requests use the emails
    //of lot owners as keys
    String lot_email= parking_lot_details.getEmail().replace(".","");

    Log.i("lot_email",lot_email);



    databaseReference.child("Requests").child(lot_email).addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {

            if (dataSnapshot.exists()) {
                long requestsMade = dataSnapshot.getChildrenCount();


                Log.i("Requests ", dataSnapshot.toString());
                Log.i("RequestsMade", Long.toString(requestsMade));
                spaceAvailable[0] = (int) (Integer.parseInt(parking_lot_details.getCapacity()) - requestsMade);

                parking_lot_details.setAvailableSpace(String.valueOf(spaceAvailable[0]));

                Log.i("Space Available ", String.valueOf(spaceAvailable[0]));
                Log.i("Space Available in met ", parking_lot_details.getAvailableSpace());


            }else{

                //if the email does not appear under requests then we assume that no requests have
                //been made and the available space is equal to the lots capacity
                parking_lot_details.setAvailableSpace(parking_lot_details.getCapacity());
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });



}

数据库

日志

after trying suggested fix

Answer 1

为了让它工作，请像这样更改第二个查询:

databaseReference.child("Requests").child(lot_email).addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {

        if (dataSnapshot.exists()) {
            long requestsMade = dataSnapshot.getChildrenCount();
            Log.d("TAG", dataSnapshot.getKey() + " / No. of childrens: " + requestsMade);

            for(DataSnapshot ds : dataSnapshot.getChildren()) {
                long childRequestsMade = ds.getChildrenCount();
                String lot_email = ds.child("lot_email").getValue(String.class);
                Log.d("TAG", lot_email);
            }
        }else{

            //if the email does not appear under requests then we assume that no requests have
            //been made and the available space is equal to the lots capacity
            parking_lot_details.setAvailableSpace(parking_lot_details.getCapacity());
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
});

要显示这些子项中的值，您需要使用 for 循环并使用 getChildren() 方法。在此示例中，它将仅打印 lot_email。