Remove indexes that are in nested field when deleting an object

问题

I'm still on Firebase and this time I have a question related on the deletion of objects.

I have a structure like the following:

users: {
    UsErId1:{
        name: "Jack",
        email: "m@i.l"
    },
    UsErId2: { + },
    UsErId3: { + }
},
user_contacts: {
    UsErId1:{
        UsErId2: true,
        UsErId3: true
    },
    UsErId2: {
        UsErId1: true
    }
}

So if I want to delete an user I have to:

Delete the user object
Delete the user object under the user_contacts branch
Remove all the indexes from user_contacts that are pointing to that user

My performance problems comes from the point 3, because I need to iterate all the user_contacts entries to see if a user it's present in the childrens.

An example of code is the following:

private void deleteUser(String userId) {

    firebaseDatabase.getReference("users").child(userId).removeValue();
    firebaseDatabase.getReference("users_contacts").child(userId).removeValue();
    firebaseDatabase.getReference("users_contacts").addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for (DataSnapshot usersSnapshot : dataSnapshot.getChildren()) {
                for( DataSnapshot contactSnapshot : usersSnapshot.getChildren() ){
                    String contactId = contactSnapshot.getValue(String.class);
                    if( contactId.equals(userId) ){
                        contactSnapshot.getRef().removeValue();
                    }
                }
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

}

I've thought of two possible solutions:

Solution 1: Don't delete the indexes from user_contacts and when I've to load the user contacts, I've to do a call to each user to see if the user is null (has been deleted), and in that case, don't show it. By the way, this results in a dirty database.

Solution 2: create a reverse index contacts_users where I store the users for which the user I'm trying to delete is referenced. As follow:

contacts_user: {
    UsErId1: {
        UsErId2: true
    },
    UsErId2: {
        UsErId1: true  
    },
    UsErId3: {
        UsErId1: true
    }
}

So, when I have to delete a user, I will look at its childs in contacts_users and know every users that has it in its contacts, and proceed to delete it (now that I can know the entire path). This seems to me to be a more NoSql-like approach.

What do you think? Is there another way to do it?

回答1:

Your second solution is how I would suggest doing it, no need to search. You could store that information on a per user basis, but if it grows too large having it elsewhere is better.

Likewise deleting in the other direction also becomes easier.

来源：https://stackoverflow.com/questions/39850117/remove-indexes-that-are-in-nested-field-when-deleting-an-object

标签

android

firebase

firebase-realtime-database

nosql