java - 无法使用 Cloud Firestore 按时间顺序排序数据

Question

我了解 Cloud Firestore 不会自动按顺序排序数据。我创建了一个值，它本质上是将纪元转换为小时。我想按此值对查询的数据进行排序:

    Query queryStore = FirebaseFirestore.getInstance()
            .collection(POLLS_LABEL)
            .orderBy("epoch", Query.Direction.DESCENDING);

我发现我的数据没有按照我希望的方式排序。不确定我是否需要在代码中添加特殊注释，但我想它就像上面一样简单。以下是我的模型:

@com.google.firebase.firestore.IgnoreExtraProperties
public class Poll {

private String question;
private String image_URL;
private String user_ID;
private String display_name;
private int vote_count;
private Long epoch;
private long trend_score;
@ServerTimestamp
private Date date;

private ArrayList<String> answers;

public Poll() {
}

public Poll(String Question, String Image_URL, ArrayList<String> answers, int vote_count, String UserID, String DisplayName, Long epoch, long trend_score, Date date
            ) {
    this.question = Question;
    this.image_URL = Image_URL;
    this.answers = answers;
    this.vote_count = vote_count;
    this.user_ID = UserID;
    this.display_name = DisplayName;
    this.epoch = epoch;
    this.trend_score = trend_score;
    this.date = date;
}

public String getUser_id() {
    return user_ID;
}

public String getDisplay_name() {
    return display_name;
}

public String getQuestion() {
    return question;
}

public void setQuestion(String question) {
    this.question = question;
}

public String getImage_URL() {
    return image_URL;
}

public Long getEpoch() {
    return epoch;
}

public void setEpoch(Long epoch) {
    this.epoch = epoch;
}

public void setUser_id(String user_id) {
    this.user_ID = user_id;
}

public void setDisplay_name(String display_name) {
    this.display_name = display_name;
}

public void setImage_URL(String image_URL) {
    this.image_URL = image_URL;
}

public Integer getVote_count() {
    return vote_count;
}

public void setVote_count(Integer vote_count) {
    this.vote_count = vote_count;
}

public long getTrend_score() {
    return trend_score;
}

public void setTrend_score(long trend_score) {
    this.trend_score = trend_score;
}

@Exclude
public Map<String, Object> toMap() {
    HashMap<String, Object> result = new HashMap<>();
    result.put("question", question);
    result.put("image_URL", image_URL);
    result.put("vote_count", 0);
    result.put("user_ID", user_ID);
    result.put("display_name", display_name);
    result.put("epoch", epoch);
    result.put("trend_score", trend_score);
    return result;
}

创作:

final Poll poll = new Poll(mCreatePollQuestion.getText().toString(), resultImageURL, mPollAnswers, 0, ID, displayName, currentEpoch, intialQS, FieldValue.serverTimestamp());

添加到 Firestore:

      mStoreBaseRef.collection(POLLS).add(poll).addOnCompleteListener(new OnCompleteListener<DocumentReference>() {
                @Override
                public void onComplete(@NonNull Task<DocumentReference> task) {
                    if (task.isSuccessful()) {
                        DocumentReference docRef = task.getResult();
                        String key = docRef.getId();
                        Log.v("KEY", key);
                        Toast.makeText(getApplicationContext(), key, Toast.LENGTH_LONG).show();
                        CollectionReference pollAnswerRef = mStoreBaseRef.collection("Polls").document(key).collection("answers");
                        //TODO: need to add answers
                        for (int i = 0; i < mPollAnswers.size(); i++){
                            pollAnswerRef.document(String.valueOf(i + 1)).set((poll.answerConvert(mPollAnswers, i)), SetOptions.merge());
                        }

                    }
                }

Answer 1

您猜对了，您应该使用注释，但您的 epoch 对象不应不为 Long 类型，而是 Date。因此，在您的 Poll 类中，请更改以下代码行:

private Long epoch;

至

@ServerTimestamp
private Date date;

我将该date 对象命名为date，因为该对象的类型是Date 而不再是纪元。当您创建Pool类的对象时，不需要设置日期。 Firebase 服务器将读取您的日期字段，因为它是 ServerTimestamp(请参阅注释)，并相应地使用服务器时间戳填充该字段。

添加日期的另一个解决方案是使用Map 和 FieldValue.serverTimestamp()像这样:

Map<String, Object> map = new HashMap<>();
map.put("date", FieldValue.serverTimestamp());
docRef.update(map).addOnCompleteListener(new OnCompleteListener<Void>() {/* ... */}