How to implement unique constraint on a child value of a node in Firebase?

Question

In my app I have to store students information having roll number attribute.I want to prevent users to enter duplicate roll number.So guide me how can I implement logic to ensure rollno to be unique. Image to reflect tree is as follows.

Sir! These roll numbers are not system generated, these are entered by students explicitly.My motive is to learn about unique constraint on 'roll_no' child of all nodes of1th_role. — Rai Mashhood Qadeer Bhatti, Apr 26 '18 at 09:51
Another option could be to change your datastructure to have a list of roll numbers (as keys) with userid as value — André Kool, Apr 26 '18 at 10:36
Making a property value unique requires that you: 1) add a data structure where you use those values as the keys (this automatically ensures they're unique), 2) use a transaction or multi-location update when updating these value. For more on this see: https://stackoverflow.com/q/35243492, https://stackoverflow.com/q/41443767, https://stackoverflow.com/q/25294478, https://stackoverflow.com/q/39149216 — Frank van Puffelen, Apr 26 '18 at 13:26

score 2 · Accepted Answer · answered Apr 26 '18 at 10:07

2

Try the following:

DatabaseReference ref=FirebaseDatabase.getInstance().getReference().child("user_detail").child("1th_role");
ref.orderByChild("roll_no").equalTo(number_entered).addValueEventListener(new ValueEventListener(){
 @Override
public void onDataChange(DataSnapshot dataSnapshot){
  if(dataSnapshot.exist() {

       Toasty.makeText(Activity_Name.this,"Number already exists",Toast.LENGTH_SHORT).show();

      }
     else{
            //add data
         }

    }
 @Override
public void onCancelled(DatabaseError databaseError) {

  }
});

Since the student will enter the number, then do a query orderByChild("roll_no").equalTo(number_entered) that checks if the roll number that is entered already exists in the database.

answered Apr 26 '18 at 10:07

Peter Haddad

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Thanks a lot .It works for me.But Sir is there any way to implement constraints on a child on server side. Instead of checking for child on client side. – Rai Mashhood Qadeer Bhatti Apr 26 '18 at 10:25
What do you mean by adding a constraint? – Peter Haddad Apr 26 '18 at 10:27
2

Sir! I have worked on mysql. And as we specifiy unique value constraint on a table field while creating a table that is why I expecting that feature in firebase. – Rai Mashhood Qadeer Bhatti Apr 26 '18 at 10:31
oh okay, yes there is no concept of primary key/unique constraint in firebase. It is also nosql – Peter Haddad Apr 26 '18 at 10:38

How to implement unique constraint on a child value of a node in Firebase?

1 Answers1