Converting SQLite query to Firebase database query

Question

I developed this app for my senior project and used SQLite and stored everything locally. I want to convert everything to Firebase now but there aren't that many tutorials out there, at least for what I'm trying to do. My question is how would I go about converting a query like the below to a Firebase database query?

public ArrayList<String> getAllBeautyItems() {

    itemsList.clear();

    dbHelper.getReadableDatabase();

    ArrayList<String> itemNames = new ArrayList<>();

    String[] tableColumns = new String[]{
            Constants.ITEM_NAME, Constants.CATEGORY
    };
    String whereClause = Constants.CATEGORY + "=?";
    String[] whereArgs = new String[]{
            "beauty"
    };

    Cursor result = db.query(Constants.ITEMS_TABLE_NAME, tableColumns, whereClause, whereArgs,
            null, null, null, null);


    if (result.moveToFirst()) {
        do {


       itemNames.add(result.getString(result.getColumnIndex(Constants.ITEM_NAME)));


        } while (result.moveToNext());

    }

    result.close();


    return itemNames;

}

and then in a fragment I'm calling a setName, so how do I get the result of that query and apply it like in the below?

 private ArrayList<Items> refreshData() {
    dbItems.clear();

    final ArrayList<String> itemNames = adapter.getAllBeautyItems();
    ArrayList<String> itemImages = adapter.getAllBeautyImages();
    ArrayList<Integer> itemPrices = adapter.getAllBeautyPrices();
    ArrayList<String> itemDescriptions = adapter.getAllBeautyDescriptions();
    ArrayList<String> itemLocations = adapter.getAllBeautyLocations();
    ArrayList<String> itemLats = adapter.getAllBeautyLats();



    int totalItems = adapter.getTotalBeautyItems();
    String formattedItems = Utils.formatNumber(totalItems);

    totalItemsText.setText("Total Items: " + formattedItems);


    ArrayList<Items> items = new ArrayList<>();


    for (int i = 0; i < itemNames.size(); i++) {

        Items item = new Items();

        item.setItemName(itemNames.get(i));
        item.setItemImage(itemImages.get(i));
        item.setItemPrice(itemPrices.get(i));
        item.setItemDescription(itemDescriptions.get(i));
        item.setItemLocation(itemLocations.get(i));
        item.setLatLocation(itemLats.get(i));

        items.add(item);

    }

    return items;

}

Answer 1

First of all, I wanna recommend you this: https://firebase.googleblog.com/2013/10/queries-part-1-common-sql-queries.html

It's a tutorial that show you how yo make typical SQL queries in Firebase, BUT, like the owner says:

While this post still contains some useful and relevant information, we have released advanced query functionality which solves a lot of the problems this post discusses.

So, now, I will tell you the basic query that may solve your problem.

As I see, you have a table about Items, and you are doing a SELECT where that item's Category is beauty.

I will assume that you already know how data is stored in Firebase, so I'm not making us lose time explaining to you about the database tree.

---

Reading

You will need something like:

Query query = FirebaseDatabase.getInstance().getReference()
                .child("items")
                .orderByChild("Category")
                .equalTo("beauty");

This, after attaching the listener to it, will search in the items tree, those items where the value of its category child, is beauty. The logic here is:

1. FirebaseDatabase.getInstance().getReference() -> Go to the main node
2. .child("items") -> Go to the Items node
3. .orderByChild("Category") -> Order them by its Category child
4. .equalTo("beauty") -> Look only at those with the "beauty" value

You will always need to do an orderBy*() to append an equalTo() and mimic the WHERE clause.

And, in your listener you will have something like:

ValueEventListener eventListener = new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            if (dataSnapshot.exists()) {
                List<Item> list = new ArrayList<>();

                for (DataSnapshot snapshot : dataSnapshot.getChildren()) {

                    Item item = snapshot.getValue(Item.class);
                    list.add(item);

                }
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            //
        }
    };
query.addValueEventListener(eventListener);

And, since all Firebase connections are async, you will need a calback method to return the list after the for.

---

Writing

Now, for the upload, you will need a DatabaseReference, instead of a Query, like:

DatabaseReference ref = FirebaseDatabase.getInstance().getReference().child("items");

And all you need to do is:

• ref.push().setValue(item); -> For a random ID
• ref.child(key).setValue(item); -> For an specific ID (key)