根据外键从firebase中取数据

Question

I am using firebase realtime DB and I would like to fetch data based on categoryId.

Here's the Db structure.

Here's the code:

  Future<void> fetchAndSetProducts(String id) async { 
const url = 'https://random-9006.firebaseio.com/products.json';
try {
  final response = await http.get(url);
  final extractedData = json.decode(response.body) as Map<String, dynamic>;
  print(extractedData.toString()); 
}

How to construct the URL in order to get the products per the categoryId passed?

Answer 1

You can use the following plugin to fetch data from firebase:

Inside pubspec.yaml :

dependencies:
  firebase_database: ^4.1.1
  firebase_core: ^0.5.0+1

in main() function initialize Firebase:

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}

Then you can get the data using the following way:

Future<DataSnapshot> getData(String category){
 var dbRef = FirebaseDatabase.instance.reference().child("products");
 return await dbRef.orderByChild("categoryId").equalTo(category).once();
}

You can then call this future method inside a FutureBuilder . For FutureBuilder check:

https://flutter.dev/docs/cookbook.networking/fetch-data#5-display-the-data

https://api.flutter.dev/flutter/widgets/FutureBuilder-class.html

Answer 2

I figured it out.

You make the URL data type final and the URL becomes:

 final url = 'https://mydburl.firebaseio.com/products.json?orderBy="categoryId"&equalTo="$id"';