将服务器时间戳字段添加到要添加的对象中 [英] Adding Server Timestamp field to the Object which being added

问题描述

我有一个Challenge对象，该对象具有它自己的属性，并且可以像这样将其成功添加到数据库中:

I have a Challenge object, which has it's own properties and I'm able to add it to the database successfully like this:

DocumentReference challengeRef=usersRef.document(loggedUserEmail).collection("challenges_feed").
                document(callengeID);
challengeRef.set(currentChallenge);

这是数据库中的样子:

我想在数据库中创建一个名为latestUpdateTimetamp的新字段(在此挑战下).这是应该的样子(我已经手动添加了):

I'd like to make a new field in the database (under this challenge) which called latestUpdateTimetamp. This is how it should look like (I have added it manually):

我试图像这样在object的constructor中设置它:

I have tried to set it in the constructor of the object like this:

private Map<String,String> latestUpdateTimestamp;

public Challenge(String id, String senderName,  String senderEmail) {   
            this.senderName=senderName;
            this.senderEmail = senderEmail;

            this.latestUpdateTimestamp= ServerValue.TIMESTAMP;
        }

但这就是我在database中得到的:

But this is what I get in the database:

我正在尝试在同一调用中将latestUpdateTimestamp添加到Challenge并将Challenge对象本身添加到数据库.有可能吗?

I'm trying to add the latestUpdateTimestamp to the Challenge and the Challenge object itself to the database at the same call. Is it possible?

我可以以某种方式将此timestamp作为属性添加到此object之前吗?

Can I somehow add this timestamp as a property to this object before adding it?

我知道我可以打一个新电话并添加此字段，但是我想知道是否有可能一次.

I know I'm able to make a new call and add this field, but I'm wondering if it's possible at once.

推荐答案

是的，可以使用Map.首先，根据官方文档，使用如下所示的注释将是必要的:

Yes you can, using a Map. First of all, according to official docs it will be necessary to use an annotation that looks like this:

@ServerTimestamp Date time;

用于标记要用服务器时间戳填充的日期"字段的注释.如果正在写入的POJO包含@ServerTimestamp注释字段的null，它将被服务器生成的时间戳替换.

Annotation used to mark a Date field to be populated with a server timestamp. If a POJO being written contains null for a @ServerTimestamp-annotated field, it will be replaced with a server-generated timestamp.

这是如何同时用服务器时间戳更新latestUpdateTimestamp字段和使用所需的值更新challangeId的方法.

This is how you can update the latestUpdateTimestamp field with the server timestamp and the challangeId with the desired value at the same time.

DocumentReference senderRef = challengeRef
    .document(loggedUserEmail)
    .collection("challenges_feed")
    .document(callengeID);

Map<String, Object> updates = new HashMap<>();
updates.put("latestUpdateTimestamp", FieldValue.serverTimestamp());
updates.put("challangeId", "newChallangeId");
senderRef.update(updates).addOnCompleteListener(new OnCompleteListener<Void>() {/* ... */}

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