如果已设置，如何避免设置 firestore 文档字段答案

【问题标题】：How to avoid setting firestore document fields if already set如果已设置，如何避免设置 firestore 文档字段
【发布时间】：2019-08-14 04:12:06
【问题描述】：

每次活动开始时，Firebase 文档字段都会重置，我需要它们持续存在。

正在使用“setOptions.merge()”在 onResume 中创建集合和文档，其中文档值设置为字符串为 null，数组为 emptyList。

    @Override
    protected void onResume() {
        super.onResume();

        //Creating the document if it does not already exist.

        Map<String, Object> read_book = new HashMap<>();
        read_book.put("read_pages", Collections.emptyList());
        read_book.put("total_pages", null);

        fireStoreDB.collection("user_" + user.getId).document("book_" + book.getId())
                .set(read_book, SetOptions.merge())
                .addOnSuccessListener(aVoid ->
                        Log.d("Activity", "FirestoreDB => created empty read_pages and total_pages"))
                .addOnFailureListener(e ->
                        Log.d("Activity", "Firestore failed to create empty read_pages and total_pages" + e));
    }

private void pageFlip(String currentPage, String totalPages){

        // Add read page to array (no duplicates)

        fireStoreDB.collection("user_" + user.getId).document("book_" + book.getId())
                .update("read_pages", FieldValue.arrayUnion(currentPage))
                .addOnSuccessListener(aVoid ->
                        Log.d("Activity", "FirestoreDB => updated read_pages " + currentPage))
                .addOnFailureListener(new OnFailureListener() {
                    @Override
                    public void onFailure(@NonNull Exception e) {
                        Log.d("Activity", "FirestoreDB => failed to update read_pages" + e);
                    }
                });

        // Set total book pages number

        fireStoreDB.collection("user_" + user.getId).document("book_" + book.getId())
                .update("total_pages", totalPages)
                .addOnSuccessListener(aVoid ->
                        Log.d("Activity", "FirestoreDB => updated total_pages " + totalPages))
                .addOnFailureListener(new OnFailureListener() {
                    @Override
                    public void onFailure(@NonNull Exception e) {
                        Log.d("Activity", "FirestoreDB => failed to update total_pages" + e);
                    }
                });
}

使用上面的代码，每次调用 onResume 时，该字段都会被重置为 null 和空列表。

我需要 total_pages 值和 read_pages 数组在 Activity 重新启动时保持不变，并可以使用 FieldValue.arrayUnion 向 read_pages 数组添加新值。

实现我的用例的有效方法是什么？

【问题讨论】：

标签： android firebase google-cloud-firestore

【解决方案1】：

你可以直接使用 set 方法和 SetOptions.merge() 不需要用空值初始化

private void pageFlip(String currentPage, String totalPages){

  Map<String, Object> data = new HashMap<>();
        data.put("total_pages", totalPages);
        data.put("read_pages", FieldValue.arrayUnion(currentPage));


        // Add read page to array (no duplicates)

        fireStoreDB.collection("user_" + user.getId).document("book_" + book.getId())
                .set(data, SetOptions.merge())
                .addOnSuccessListener(aVoid ->
                        Log.d("Activity", "FirestoreDB => updated read_pages " + currentPage))
                .addOnFailureListener(new OnFailureListener() {
                    @Override
                    public void onFailure(@NonNull Exception e) {
                        Log.d("Activity", "FirestoreDB => failed to update read_pages" + e);
                    }
                });


}

【讨论】：