android firebase：Firebase 数据库中的 NOT EQUAL 查询

Question

我有如下用户对象：

{
  "deviceTokens" : {
    "SgJd7o1hK7YbJnygnYWvaz4qkr42" : {
      "c-sfcTB3iEA:APA91bEvuzhX1nlrhoxVmR69lvwu0H1zyRjOXd5b14LngObuj8WeHkmlel6AOyrU7B2alBO1vW0pIO4gXGurvz5llCloyYpQv7vCq0_3fVEhmrIGfJ2S13TiXqVLJgWUCs95_AYZlysj" : true,
      "cnQdyuxBgz0:APA91bFZTPEFrl1Vf9Nw9ZvdtNsW1ll3YYq8WIwT799NVTp6S281v56UVJ3lo0kDK_rFZfoHuarX9Qb8NL8TJXi9A_jH4RhbDp3ecbW-tHdrYR06PwYdSiMfRjIxJOuPtHuqy0TNOw4K" : true,
      "d3D81crwy0E:APA91bEoAeWiOwm73bt2DvNNdv_NUn0PwjQcLa6z8ZYjDyuHWsNeDPVDCXOATKB5AFoBb7iOW6kgzU41oYFqHYek1Cngv6ArsrZO0crq_bV3PzfQxKvRN8xYX1_WryaR2tpAVP_4czgx" : true,
      "dHBaxzKqhMw:APA91bGmQ5KhxiaE48_IQHEJVpvpvQdXUgAd_a1reJiyh4Z5W6dhNZB4KesaQuiRrj-VLxdCvxIroH3a-75zUaYd6_yLtoCzNfNGT8EWqUrtC3FSibOA_cwPye09C001zfFe_pHv6Wph" : true,
      "dz8wf231cXE:APA91bEAmfPu4QWRstKE5kqtN-UtgNpOIG7KWxsjFB1oIOp9cKhoWfbnpsvMTd3YgNw09jVNK6lUgKXMNt4AND0cZGcepkqQyZTDNh5KA5SU9KbbD7MJzxGhwGhGlFV-4hiOOhumoRxs" : true
    }
  },
  "users" : {
    "SgJd7o1hK7YbJnygnYWvaz4qkr42" : {
      "displayName" : "Chintan Soni",
      "email" : "chintansoni202@gmail.com",
      "photoUrl" : "https://lh5.googleusercontent.com/-JNfSscqwEng/AAAAAAAAAAI/AAAAAAAADbs/dj7t_7AYlzo/s96-c/photo.jpg"
    }
  }
}

我可以使用以下方法查询用户对象：

mDatabaseReference = FirebaseDatabase.getInstance().getReference().child("users");

我想知道是否有查询不等式的方法。我想查询用户的孩子的密钥与我的 FirebaseUser UID 不匹配，这意味着我想获取除我之外的用户的记录。

Answer 1

其实我并不想创建自己的适配器，因为我相信 FirebaseUI 不会有这样的限制，但我错了。 无论如何，这就是我接近的方式：

首先从 FirebaseDatabase 中获取用户对象中的所有数据，然后在我们端进行过滤，最后设置该数据：

FirebaseDatabase.getInstance().getReference().child("users")
   .addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            Iterable<DataSnapshot> list = dataSnapshot.getChildren();

            // Getting current user Id
            String uid = getCurrentUserId();

            // Filter User
            List<User> userList = new ArrayList<>();
            for (DataSnapshot dataSnapshot1 : list) {
                if (!dataSnapshot1.getKey().equals(uid)) {
                    userList.add(dataSnapshot1.getValue(User.class));
                }
            }

            // Setting data
            mBaseRecyclerAdapter.setItems(userList);
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

我在这里创建了自己的通用回收器适配器： https://gist.github.com/chintansoni202/3c61aea787ae4bd49f26adee9dd40a08

Answer 2

解决这个问题并仍然使用 FirebaseUI 中的 FirebaseRecyclerAdapter 的一种方法是像这样扩展 FirebaseArray：

import com.firebase.ui.database.FirebaseArray;
import com.firebase.ui.database.SnapshotParser;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.Query;

import java.util.HashSet;
import java.util.Set;

public class FilterableFirebaseArray extends FirebaseArray {

    private Set<String> excludes = new HashSet<>();

    public FilterableFirebaseArray(Query query, Class aClass) {
        super(query, aClass);
    }

    public FilterableFirebaseArray(Query query, SnapshotParser parser) {
        super(query, parser);
    }

    public void addExclude(String key) {
        excludes.add(key);
    }

    public void removeExclude(String key) {
        excludes.remove(key);
    }

    @Override
    public void onChildAdded(DataSnapshot snapshot, String previousChildKey) {
        if (!excludes.contains(snapshot.getKey())) {
            super.onChildAdded(snapshot, excludes.contains(previousChildKey)? null : previousChildKey);
        }
    }

    @Override
    public void onChildChanged(DataSnapshot snapshot, String previousChildKey) {
        if (!excludes.contains(snapshot.getKey())) {
            super.onChildChanged(snapshot, excludes.contains(previousChildKey)? null : previousChildKey);
        }
    }

    @Override
    public void onChildMoved(DataSnapshot snapshot, String previousChildKey) {
        if (!excludes.contains(snapshot.getKey())) {
            super.onChildMoved(snapshot, excludes.contains(previousChildKey)? null : previousChildKey);
        }
    }

    @Override
    public void onChildRemoved(DataSnapshot snapshot) {
        if (!excludes.contains(snapshot.getKey())) {
            super.onChildRemoved(snapshot);
        }
    }

}

...然后像这样使用它：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    RecyclerView userListView = (RecyclerView) findViewById(R.id.userList);
    userListView.setLayoutManager(new LinearLayoutManager(this));

    DatabaseReference ref = FirebaseDatabase.getInstance().getReference();
    Query query = ref.orderByValue();
    ClassSnapshotParser parser = new ClassSnapshotParser<UserProfile>(UserProfile.class);
    FilterableFirebaseArray filterableFirebaseArray = new FilterableFirebaseArray(query, parser);

    filterableFirebaseArray.addExclude(FirebaseAuth.getInstance().getCurrentUser().getUid());

    FirebaseRecyclerAdapter mAdapter = new FirebaseRecyclerAdapter<UserProfile, UserListEntryHolder>(
            filterableFirebaseArray,
            R.layout.userlist_entry,
            UserListEntryHolder.class) {
        @Override
        protected void populateViewHolder(UserListEntryHolder viewHolder, UserProfile model, int position) {
            viewHolder.bind(model);
        }
    };
    userListView.setAdapter(mAdapter);
}

“魔法”发生在被覆盖的 onChildAdded 方法中，我们忽略了由指定键标识的子项。在此示例中，我只是将当前用户的 UID 添加到排除列表中。因为这符合我的数据库设计。

您可以轻松扩展功能以忽略具有特定属性的子项。

奖励：如果您更喜欢 Kotlin 方式（像我一样），您会这样做：

import com.firebase.ui.database.FirebaseArray
import com.firebase.ui.database.SnapshotParser
import com.google.firebase.database.DataSnapshot
import com.google.firebase.database.Query

class FilterableFirebaseArray<T> : FirebaseArray<T> {

    val excludedKeys = HashSet<String?>()

    constructor(query: Query, tClass: Class<T>) : super(query, tClass)
    constructor(query: Query, parser: SnapshotParser<T>) : super(query, parser)

    override fun onChildAdded(snapshot: DataSnapshot, previousChildKey: String?) {
        if (!excludedKeys.contains(snapshot.key))
            super.onChildAdded(snapshot, if (excludedKeys.contains(previousChildKey)) null else previousChildKey)
    }

    override fun onChildChanged(snapshot: DataSnapshot, previousChildKey: String?) {
        if (!excludedKeys.contains(snapshot.key))
            super.onChildChanged(snapshot, previousChildKey)
    }

    override fun onChildMoved(snapshot: DataSnapshot, previousChildKey: String?) {
        if (!excludedKeys.contains(snapshot.key))
            super.onChildMoved(snapshot, previousChildKey)
    }

    override fun onChildRemoved(snapshot: DataSnapshot) {
        if (!excludedKeys.contains(snapshot.key))
            super.onChildRemoved(snapshot)
    }

}

...然后像这样使用它：

override fun onStart() {
    super.onStart()
    if (currentUser != null) {
        userList.adapter = getAdapter()
    }
}

private fun getAdapter(): FirebaseRecyclerAdapter<UserProfile, UserListEntryHolder> {

    val query = userProfilesReference.orderByValue()
    val parser = ClassSnapshotParser<UserProfile>(UserProfile::class.java)
    val filterableFirebaseArray = FilterableFirebaseArray<UserProfile>(query, parser)

    filterableFirebaseArray.excludes.add(currentUser?.uid)

    return object : FirebaseRecyclerAdapter<UserProfile, UserListEntryHolder>(
            filterableFirebaseArray,
            R.layout.userlist_entry,
            UserListEntryHolder::class.java) {
        public override fun populateViewHolder(entryHolder: UserListEntryHolder, userProfile: UserProfile, position: Int) {
            entryHolder.bind(userProfile)
        }
    }
}

更新代码以解决与 onChildChanged、onChildMoved 等相关的 IllegalArgumentExceptions。