Firebase查询不会显示所有数据

Question

I need to get all users of a determined age range, but my code does not work.

My Firebase database structure is this.

-user
   -1
      -name:"James"
      -age:"21"

   -2
      -name:"Artur"
      -age:"25"

   -3
      -name:"Charlotte"
      -age:"25"

   -3
      -name:"Marvin"
      -age:"80"

My code is this. With this I just catch 1 user.

DatabaseReference uRef = database.getReference("users");

Query UserQuery = uRef.orderByChild("age").startAt(21).endAt(50);

    UserQuery.limitToFirst(10).addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {

            int counter =(int) dataSnapshot.getChildrenCount();

            Log.d("TAG////////", String.valueOf(counter));




        }


        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

But if I delete the endAt() condition, I catch all users after 21 and I just wanna catch the users in the range.

DatabaseReference uRef = database.getReference("users");

Query UserQuery = uRef.orderByChild("age").startAt(21); //I deleted endAt(50);

    UserQuery.limitToFirst(10).addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {

            int counter =(int) dataSnapshot.getChildrenCount();

            Log.d("TAG////////", String.valueOf(counter));




        }


        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

Please help me.

Answer 1

It looks like you store the age as a string value, so you should also pass a string into the query:

Query UserQuery = uRef.orderByChild("age").startAt("21").endAt("50");

---

Note that this will lead to problems when you want to get everyone from age 2 to 5, since in lexicographical sorting that looks like:

"18"
"19"
"2"
"20"
"21"
"22"
...
"29"
"3"
"30"
"31"
...

So you'll probably want to fix that by storing the ages as actual numeric values, instead of storing them as a string.