Question

在尝试更新值和编写文档之前，我试图在Firestore事务中检索文档，但是无论何时启动事务，我都会不断从快照中获取空值。但是，当我尝试获取文档ID时，实际上我确实拥有它。

基本上，我想检索在服务中心子集合中创建的最后一个计数器（按编号），该计数器被另存为服务中心文档本身中的属性，并使用新编号创建一个计数器，同时还要更新“ lastCounter”属性在服务中心。

我将“ lastCounter”检索为双精度，我尝试使用long，但它不起作用。我也无法获得其他任何属性。

            DocumentReference scReference = db
                    .collection("Services")
                    .document(uuid);

            Log.i("AAA", "STARTED TRANSACTION");

            // get the service centre
            DocumentSnapshot serviceCenterSnapshot = transaction.get(scReference);

            Log.i("AAA", serviceCenterSnapshot.getId()); // this one retireves the id which shows that it's working

            Log.i("AAA", "last counter = " + serviceCenterSnapshot.getDouble("lastCounter")); // null
            Log.i("AAA", "branch = " + serviceCenterSnapshot.getString("branch")); // null
            ```
            // get the last counter added and increment it
            double lastCounterNumber = serviceCenterSnapshot.getDouble("lastCounter");
            double newCounterNumber = lastCounterNumber + 1;

            Counter counter = new Counter(newCounterNumber);

            // update the service centre with the last counter added
            transaction.update(scReference, "lastCounter", newCounterNumber);

            // add the new counter
            transaction.set(scReference.collection("Counters").document(), counter);
            return null;

日志

2019-04-01 18:05:32.966 29597-29656/com.zayed.qmsadmin I/AAA: STARTED TRANSACTION
2019-04-01 18:05:33.405 29597-29656/com.zayed.qmsadmin I/AAA: rkO0i0sQHuWFWqNUb8J3XE1QV6E3
2019-04-01 18:05:33.405 29597-29656/com.zayed.qmsadmin I/AAA: last counter = null
2019-04-01 18:05:33.405 29597-29656/com.zayed.qmsadmin I/AAA: branch = null
2019-04-01 18:05:33.406 29597-29597/com.zayed.qmsadmin I/AAA: FINISHED TRANSACTION
2019-04-01 18:05:33.406 29597-29597/com.zayed.qmsadmin I/AAA: Attempt to invoke virtual method 'double java.lang.Double.doubleValue()' on a null object reference

在Android Firestore中通过事务检索数据后获取null

0 个答案: