How to get specific child data from firebase

问题

I have need to access a specific child from node, i have only "available key" of the specific child not complete path.

回答1:

Since you know the key of the child you're looking for, you can query on that:

DatabaseReference schoolsRef = FirebaseDatabase.getInstance().getReference().child("School");
Query query = schoolsRef.orderByKey().equalTo("MZ3bW5kLJAQorgnZbYiTaOoWWSG2");

db.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        for (DataSnapshot userSnapshot: dataSnapshot.getChildren()) {
            String email = userSnapshot.child("email").getValue(String.class);
        }
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        throw databaseError.toException();
    }
});

Note that you can't use orderByChild("id") as explained in my answer here: Firebase Query Double Nested.

回答2:

Just add this code:

DatabaseReference db = FirebaseDatabase.getInstance().getReference().child("school").child(firebaseUser.getUid();

db.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                String email = dataSnapshot.child("Email").getValue().toString();
            }

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

            }
        });

回答3:

try this :-

DatabaseReference mUserNameReference = FirebaseDatabase.getInstance().getReference("School").child("id").child("id");
    mUserNameReference.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                    String email = dataSnapshot.child("email").getValue().toString());
                   //get all the key value like this
                }

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

                }
            });

回答4:

If you have key for that child but not complete path first get key of parent node in list like below I did.

 Arraylist<String> keyList =new Arraylist();
      DatabaseReference db = FirebaseDatabase.getInstance().getReference().child("school").child(firebaseUser.getUid();

        db.addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                        for (DataSnapshot childSnapshot : dataSnapshot.getChildren()) {
                String key = childSnapshot.getKey();

                String value=  childSnapshot.getValue(String.class);

                keyList.add(key);

            }
                    }

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

                    }
                });

now use for loop or foreach loop to check if that node contains available child key.

for(String key:keyList){



 DatabaseReference db = FirebaseDatabase.getInstance().getReference().child("school").child(key).orderByChild("id").equal(availableKey);

            db.addValueEventListener(new ValueEventListener() {
                        @Override
                        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                            for (DataSnapshot childSnapshot : dataSnapshot.getChildren()) {
                    String key = childSnapshot.getKey();

                    Object object=  childSnapshot.getValue(Object.class);



                }
                        }

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

                        }
                    });







}

hope this will help you..

来源：https://stackoverflow.com/questions/55809688/how-to-get-specific-child-data-from-firebase