如何从Firestore获取当前日期和时间并将其保存? [英] How to get the current date and time from Firestore and save it?

问题描述

我是Cloud Firestore的新手，正在尝试解决问题.我目前正在尝试为Android创建一个简单的数据库，其中包含用户的ID和用户安装该应用程序的时间，这样我就可以知道他们是否通过了试用期.除了获取日期和时间(我想从服务器获取日期和时间)之外，其他一切看起来都非常简单.人们说我应该使用:

I'm new to Cloud Firestore and trying to figure things out. I'm currently trying to create a simple database for Android that contains the ID of a user and the time they installed the app so I can know if they passed their trial period. Everything seems very simple except getting the date and time (which I want to get from the server). People are saying I should use:

FieldValue.serverTimestamp()

但是其他人说这对添加用户无效.另外，此方法返回一个称为"FieldValue"的东西，它可以用来将用户的日期和时间与当前日期和时间进行比较吗?

But others say that doesn't work for adding a user. Also, this method returns something called "FieldValue", what is that, and can it be used to compare the user's date and time with the current date and time?

String deviceId = Settings.Secure.getString(getContentResolver(), Settings.Secure.ANDROID_ID);
    
FirebaseFirestore db = FirebaseFirestore.getInstance();
// Create a new user with an ID and time
Map<String, Object> user = new HashMap<>();
user.put("userID", deviceId);
user.put("timeStamp", FieldValue.serverTimestamp());

// Add a new document with a generated ID
db.collection("users")
    .add(user)
    .addOnSuccessListener(new OnSuccessListener<DocumentReference>() {
        @Override
        public void onSuccess(DocumentReference documentReference) {
            Log.d("document", "DocumentSnapshot added with ID: " + documentReference.getId());
            }
        })
        .addOnFailureListener(new OnFailureListener() {
            @Override
            public void onFailure(@NonNull Exception e) {
                Log.w("document", "Error adding document", e);
            }
        });

推荐答案

首先，使用"deviceId"作为Firestore中用户的唯一标识符，在我看来并不是一个好主意.主要原因是用户可以在任何时间点更改设备，这意味着"users/$ deviceId/"下的所有数据都可以被替换.会迷路.因此，在这种情况下，最好的方法是使用Firebase对用户进行身份验证并用作唯一标识符，来自身份验证过程的UID.

First of all, using the "deviceId" as a unique identifier for your users in Firestore doesn't seem to me like a good idea. The main reason is that a user can change the device at any point in time, meaning that all the data under "users/$deviceId/" will be lost. So the best approach, in this case, is to authenticate your users with Firebase and use as a unique identifier the UID that comes from the authentication process.

要将用户对象写入数据库，您只需使用以下代码行即可:

To write a user object to the database, you can simply use the following lines of code:

Map<String, Object> user = new HashMap<>();
user.put("userID", deviceId);
user.put("timeStamp", FieldValue.serverTimestamp());
String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
CollectionReference usersRef = rootRef.collection("users");
usersRef.document(uid).set(user).addOnSuccessListener(/* ... */);

现在，要读回"timeStamp"的值，则将其重新设置为0.属性，则需要使用"get()"调用，如以下代码行所述:

Now, to read back the value of the "timeStamp" property, you need to use a "get()" call, as explained in the following lines of code:

usersRef.document(uid).get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
    @Override
    public void onComplete(@NonNull Task<DocumentSnapshot> task) {
        if (task.isSuccessful()) {
            DocumentSnapshot document = task.getResult();
            if (document.exists()) {
                Date timeStamp = document.getDate("timeStamp");
            } else {
                Log.d(TAG, "No such document");
            }
        } else {
            Log.d(TAG, "get failed with ", task.getException());
        }
    }
});

具有"timeStamp"；对象，现在您可以获取当前日期和时间并根据需要在项目中进行比较.

Having the "timeStamp" object, now you can get the current date and time and compare them as needed in your project.

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