如何根据ID授予对Firebase数据库中某些对象的访问权限 [英] How can I give access to certain objects in Firebase database based on id

问题描述

我有这个数据结构:

红色箭头指向动物ID，蓝色箭头指向用户ID.每个用户都有一个或多个动物.

The red arrows points at animal IDs, and the blue arrow points at user IDs. Every user have one or many animals.

我尝试了不同的方法来仅显示具有存储在当前用户节点中的id的动物.

I have tried different methods for showing only the animals that have id that is stored in the current user node.

示例:如果我有UID = 48onHXIxgDP465j5WW16oo7psNm2(用户"中的第一个)，我想显示来自"dog2"和"dog3"的数据.

Example: If I have UID = 48onHXIxgDP465j5WW16oo7psNm2 (the first one in "users") I want to show the data from: "dog2" and "dog3".

现在，我拥有以下代码，这些代码从数据库中的动物"节点获取快照，然后从每个子节点获取数据.

Now iIhave the following code that gets snapshot from the "animals" node in the database, and then gets data from every child.

     myAnimalRef.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            list = new ArrayList<AnimalCard>();
            for(DataSnapshot dataSnapshot1 :dataSnapshot.getChildren()){

                AnimalCard value = dataSnapshot1.getValue(AnimalCard.class);
                AnimalCard animal = new AnimalCard();
                String name = value.getName();
                int age = value.getAge();
                String url = value.getUrl();
                animal.setName(name);
                animal.setAge(age);
                animal.setUrl(url);
                list.add(animal);

            }
            recyclerViewSetAdapter();
            progressDialog.dismiss();

        }
        @Override
        public void onCancelled(DatabaseError databaseError) {
            Log.d(TAG1, "failed to read value: " + databaseError.toException());
        }
    });

如何获取我的代码以过滤掉用户节点中没有其ID的每只动物?

How can get my code to filter out every animal that does not have their ID in the user node?

我想让用户使用存储在数据库中的UID进行访问的原因是因为稍后我要进行访问，以便多个用户可以访问同一动物.

The reason I want to make the user get access with an UID stored in the database is because later on I want to make it so that multiple users can get access to the same animal.

推荐答案

要实现此目的，您需要查询数据库两次.请使用以下代码:

To achieve this, you need to query your database twice. Please use the following code:

FirebaseUser firebaseUser = firebaseAuth.getCurrentUser();
String uid = firebaseUser.getUid();

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference uidRef = usersRef.child("users").child(uid);
ValueEventListener eventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            String aid = ds.getKey();

            DatabaseReference animalRef = rootRef.child("animals").child(aid);
            ValueEventListener valueEventListener = new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dSnapshot) {
                    int age = dSnapshot.child("age").getValue(Integer.class);
                    String name = dSnapshot.child("name").getValue(String.class);
                    String url = dSnapshot.child("url").getValue(String.class);
                    Log.d("TAG", age + " / " + name + " / " + url);
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {}
            };
            animalRef.addListenerForSingleValueEvent(valueEventListener);
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {}
};
uidRef.addListenerForSingleValueEvent(eventListener);

其中uid是已登录用户的ID，aid是动物的ID.您的输出将是:

In which uid is the id of the logged-in user and aid is the id of the animal. Your output will be:

11 / dog1 / http...
12 / dog2 / http...

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