android 如何从 firebase 数据库中检索特定节点

Question

我正在尝试在我的 android 应用程序中使用 Firebase。我正在关注 Saving and retrieving 的文档，但是教程中使用的示例数据库（Dragon）与我的数据库结构不同。

这是我将数据推送到 firebase 的代码

Firebase myFirebaseRef = new Firebase("https://myfirebaseurl.firebaseio.com/android/saving-data/fireblog");
                User userName = new User(socialNum, name, datofBirth, mob1, mob2, healthCondition);
                Firebase usersRef = myFirebaseRef.child(name);
                Map<String, User> users = new HashMap<String, User>();
                users.put(name, userName);                    
              myFirebaseRef.push().setValue(users);

创建这样的数据库格式

{
      "android" : {
        "saving-data" : {
          "fireblog" : {
            "-JiRtkpIFLVFNgmNBpMj" : {
              "Name" : {
                "birthDate" : "100",
                "fullName" : "Name",
                "healthCond" : "fyhft",
                "mob1" : "5855",
                "mob2" : "5858",
                "socialNumber" : "100"
              }
            },
            "-JiRv0RmHwWVHSOiZXiN" : {
              "mast" : {
                "birthDate" : "100",
                "fullName" : "mast",
                "healthCond" : "fyhft",
                "mob1" : "5855",
                "mob2" : "5858",
                "socialNumber" : "100"
              }
            }
          }
        }
      }
    }

我想从 firebase 中检索数据，这样，如果我将 "full Name" 放入我的应用程序搜索框中，它应该检索该特定节点，以便我可以在 Listview 中填充该信息。

这就是我试图检索的方式，

final String Find = find.getText().toString();   //Get text for search edit text box
                Firebase myFirebaseRef = new Firebase("https://myfirebaseurl.firebaseio.com/android/saving-data/fireblog");
                Query queryRef = myFirebaseRef.orderByChild("fullName");
               // System.out.println(dataSnapshot.getKey() + "is" + value.get("socialNumber"));
                System.out.println(Find);

                queryRef.addChildEventListener(new ChildEventListener() {
                    @Override
                    public void onChildAdded(DataSnapshot dataSnapshot, String previousChild) {
                        System.out.println(dataSnapshot.getValue());
                        Map<String,Object> value = (Map<String, Object>) dataSnapshot.getValue();

                        String name1 = String.valueOf(value.get("fullName"));
                    //System.out.println(dataSnapshot.getKey() + "is" + value.get("fullName").toString());
                    if (name1.equals(Find)){
                        System.out.println("Name" + value.get("fullName"));
                    }
                    else{
                        System.out.println("its is null");
                    }

                    }

但是它returns所有节点，

02-19 12:18:02.053    8269-8269/com.example.nilesh.firebasetest I/System.out﹕ name
02-19 12:18:05.426    8269-8269/com.example.nilesh.firebasetest I/System.out﹕ {Name={socialNumber=100, birthDate=100, fullName=Name, mob1=5855, mob2=5858, healthCond=fyhft}}
02-19 12:18:05.426    8269-8269/com.example.nilesh.firebasetest I/System.out﹕ its is null
02-19 12:18:05.426    8269-8269/com.example.nilesh.firebasetest I/System.out﹕ {mast={socialNumber=100, birthDate=100, fullName=mast, mob1=5855, mob2=5858, healthCond=fyhft}}
02-19 12:18:05.426    8269-8269/com.example.nilesh.firebasetest I/System.out﹕ its is null

我如何检索特定节点，以便如果我输入 fullName = mast，它应该只检索第二个节点以及该节点中的所有字段。

Answer 1

您正在这一行中创建查询：

Query queryRef = myFirebaseRef.orderByChild("fullName");

就像查询按 fullName 值对子节点排序一样。但它还没有限制返回什么子节点。

要限制节点，还得过滤。例如：

Query queryRef = myFirebaseRef.orderByChild("fullName").equalTo("gooner");

您还可以通过使用 startAt and/or endAt 而不是 equalTo.

进行过滤来获取一系列节点

正如 Kato 评论的那样：

It looks like there is a superfluous level of children. The data is structured as saving-data/fireblog/<record id>/fluff/...actual data... and the fluff layer needs to be removed for those queries to work. You can't query children of children.

Answer 2

这是使用 Hashmap 从 firebase 数据库中检索单个值的另一种方法。

     ArrayList<HashMap<String,String>> AllUserscourselist;
 String SelectedCourseUserUId;
     DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference();

     databaseReference.child("User_course_Details").addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
    //                        emergencyContactsList = new ArrayList<>();
                    AllUserscourselist = new ArrayList<HashMap<String, String>>();
                    if(dataSnapshot.exists())
                    {
                        for(DataSnapshot postSnapShot:dataSnapshot.getChildren())
                        {

                            for (DataSnapshot courseUID : postSnapShot.getChildren()){
                                UsercourseDetails usercourseDetails = courseUID.getValue(UsercourseDetails.class);
                                HashMap<String, String> map = new HashMap<String, String>();

                                String user_id = postSnapShot.getKey();
                                String course_id = usercourseDetails.getcourse_id();
                                String course_type = usercourseDetails.getcourse_type();
                                String course_brand = usercourseDetails.course_brand;
                                String course_number_plate_url = usercourseDetails.course_number_plate_url;

                                map.put("user_id", user_id);
                                map.put("course_id", course_id);
                                map.put("course_type", course_type);
                                map.put("course_brand", course_brand);
                                map.put("course_number_plate_url", course_number_plate_url);

                                AllUserscourselist.add(map);
                            }

    //                        AllUserscourselist.add(new UsercourseDetails(usercourseDetails.getcourse_type(),usercourseDetails.getcourse_brand(),usercourseDetails.getcourse_number_plate_url(),usercourseDetails.getcourse_id()));
                        }

                        Log.e("AllUserscourselist",""+AllUserscourselist);

                        courseIdList = new ArrayList<String>();
                        for (int i = 0; i < AllUserscourselist.size(); i++) {
                            String course_id_list;
                            course_id_list = AllUserscourselist.get(i).get("course_id")+" "+ AllUserscourselist.get(i).get("user_id");
                            courseIdList.add(course_id_list);
                        }

                        if(courseIdList.size()>0 && courseIdList!=null) {
                            for (int i = 0; i < courseIdList.size(); i++) {   //used
                                String arr[] = courseIdList.get(i).split(" ");
                                if (arr[0].equals(coursenumber)) {
                                    SelectedcourseUserUId = arr[1];
                                    getUserEmergencyContacts(SelectedcourseUserUId);
                                    break;
                                }
                            }
                        }

                    }else{
    //                    NavigationActivity.this.overridePendingTransition(R.anim.anim_slide_in_left, R.anim.anim_slide_in_left);
                    }
                }
                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });

Answer 3

如果你想像这样获取特定节点或子节点的值

这里如果你想获取子节点（地址）值。你可以这样获取

    FirebaseDatabase database;
    DatabaseReference myRef;
    myRef = database.getReference();
    final DatabaseReference orders_Reference = myRef.child("Order");


 orders_Reference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for (DataSnapshot data : dataSnapshot.getChildren()) {
                if(data.getKey().equals("address")){
                String orderNumber = data.getValue().toString();
                Log.d("Specific Node Value" , orderNumber);
               }
            }
        }
        @Override
        public void onCancelled(DatabaseError databaseError) {
        }
    });

Answer 4

而不是获取所有节点然后迭代它以根据值获取节点，只需触发 firebase 提供的查询即可。

   private void readAllRequestedFormFromFirebaseDb(){
    final FirebaseDatabase database = FirebaseDatabase.getInstance();
    DatabaseReference ref = database.getReference("App_DB");
    DatabaseReference childRef = ref.child("AllRequest");
    Query queryRef = 
  childRef.orderByChild("fullName").equalTo("Jay");
    queryRef.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot snapshot) {

            // getting list
            for(DataSnapshot dataSnapshot: snapshot.getChildren()){
                QueryFormModel post = dataSnapshot.getValue(QueryFormModel.class);
                queryFormModelArrayList.add(post);
                /*the above list will have record only
                 with the provided fullName as Jay*/

            }

        }
        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {
            Log.e("DetailsActivity", "onCancelled:readAllSubmittedRequestFromFirebaseDb:  "+databaseError );
        }
    });
}

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