android - 无法从 Firebase 数据库读取嵌套数据

Question

我正在发送“开胃菜和小吃”，位于 name从一项 Activity 1 到 Activity 2 的键。
在 Activity 2 中，收到的数据很简单:

intent = getIntent();
String received_id = intent.getStringExtra("cat_id");
Log.e("ID received is", received_id);

输出是:

ID received is : Appetizers and Snacks

在这个值的帮助下，我试图读取节点 recipes并在各自的 View 中显示所有数据。
我只想知道，我怎样才能到recipes节点。我试过这个直到现在:

  query = FirebaseDatabase.getInstance().getReference("All Categories").orderByChild("name").equalTo(received_id);

  query.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            Log.e("data", String.valueOf(dataSnapshot));
            if (dataSnapshot.exists()) {
                for (DataSnapshot dataSnapshot1 : dataSnapshot.child("recipes").getChildren()) {
                    Log.e("data final is ", String.valueOf(dataSnapshot1.getValue()));
                    DetailModel p = dataSnapshot1.getValue(DetailModel.class);
                    detailModelList.add(p);
                }

                detailAdapter = new DetailAdapter(DetailCategory.this, detailModelList);
                recyclerView.setAdapter(detailAdapter);
                progressBar.setVisibility(View.INVISIBLE);
            } else {
                Toast.makeText(DetailCategory.this, "No data available !", Toast.LENGTH_SHORT).show();
                Log.e("No data available !", "No data available !");
                progressBar.setVisibility(View.INVISIBLE);
            }
        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

            Toast.makeText(DetailCategory.this, databaseError.getDetails(), Toast.LENGTH_SHORT).show();
        }
    });
    recyclerView.setLayoutManager(new GridLayoutManager(DetailCategory.this, 2));

The Log.e("data", String.valueOf(datasnapshot)) gives this Output :

DataSnapshot { key = All Categories, value = {0={image=https://i.imgur.com/0toOJMa.jpg, recipes={randomkey={image=https://i.ibb.co/gvH8Vp2/5f6fg0l8-keraal-roast-chicken-62.png, servings=4 servings, ingredients="complete Ingredients here"}}, name=Appetizers and Snacks}} }

My DetailModel class is a simple class :

public DetailModel() {
}

String image,title, time,servings,ingredients,steps;
 public DetailModel(Integer id, String image, String title, String time, String servings, String ingredients, String steps) {
    this.id = id;
    this.image = image;
    this.title = title;
    this.time = time;
    this.servings = servings;
    this.ingredients = ingredients;
    this.steps = steps;
}

public Integer getId() {
    return id;
}

public String getImage() {
    return image;
}

public String getTitle() {
    return title;
}

public String getTime() {
    return time;
}

public String getServings() {
    return servings;
}

public String getIngredients() {
    return ingredients;
}

public String getSteps() {
    return steps;
}
   

但是每次在App中没有接收到数据，完全空白，连Else条件都不执行。
它不会到达 if (dataSnapshot.exists()) { 并且没有执行任何内部代码。因为，我还检查了设置日志，在 Logcat 中也没有找到任何内容。任何提示，为什么会这样？
编辑:我按照弗兰克的推荐做了，应用程序中仍然没有数据
请指导我阅读此嵌套数据。

Answer 1

取而代之的是:

databaseReference = FirebaseDatabase.getInstance().getReference("All Categories").child("name").orderByValue().equalTo(received_id).getRef();

你会想要使用:

Query query = FirebaseDatabase.getInstance().getReference("All Categories").orderByChild("name").equalTo(received_id);

所以:

使用 orderByChild("name")告诉数据库根据其 name 的值对所有子节点进行排序属性(property)。

使用 equalTo(...)然后过滤排序后的数据。

删除 getRef()因为这实际上会撤消您的所有查询构建。

然后读取数据，请执行以下操作:

query.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        if (dataSnapshot.exists()) {
            for (DataSnapshot categorySnapshot: dataSnapshot.getChildren()) {
                for (DataSnapshot recipeSnapshot: categorySnapshot.child("recipes").getChildren()) {
                    DetailModel p = recipeSnapshot.getValue(DetailModel.class);
                    detailModelList.add(p);
                }
            }

            detailAdapter = new DetailAdapter(DetailCategory.this, detailModelList);
            recyclerView.setAdapter(detailAdapter);
            progressBar.setVisibility(View.INVISIBLE);
        } else {
            Toast.makeText(DetailCategory.this, "No data available !", Toast.LENGTH_SHORT).show();
            progressBar.setVisibility(View.INVISIBLE);
        }
    }

所以:

收听我们刚刚创建的整个查询。

然后循环遍历 recipes 的 child 我们在快照中返回的每个节点。