firestore: get data from db with dart, and dynamically pass named params - v1

firestoreAPI.dart

/*
  Carlos Martinez 2021
  this is a very little library for confortable use of firestore in dart.
  version 1.0
*/

import 'package:cloud_firestore/cloud_firestore.dart';

// class for firestore `where` method, this is a trick
// because Dart doest not support pass dynamically named parameters
// so I use a simple class like a javascript plain object, to can use dot notation:
class FireWhere{
  static const String isEqualTo = "isEqualTo";
  static const String isNotEqualTo = "isNotEqualTo";
  static const String isLessThan = "isLessThan";
  static const String isLessThanOrEqualTo = "isLessThanOrEqualTo";
  static const String isGreaterThan = "isGreaterThan";
  static const String isGreaterThanOrEqualTo = "isGreaterThanOrEqualTo";
  static const String arrayContains = "arrayContains";
  static const String arrayContainsAny = "arrayContainsAny";
  static const String whereIn = "whereIn";
  static const String whereNotIn = "whereNotIn";
  static const String isNull = "isNull";
}

class FirestoreDB {
  final db = FirebaseFirestore.instance;
  
  CollectionReference getRef(String collection) => db.collection(collection);
  
  Future<List<Map<String, dynamic>>> getData(
      String collection,
      {
        String whereField = '',
        Map<String, dynamic> where,
        int limit,
        String orderBy,
        bool orderDescending = false
      }
    ) async{
      List<Map<String, dynamic>> docsList = new List<Map<String, dynamic>>();
      dynamic ref = getRef(collection);

      // Dart doest not support pass dynamically named parameters
      // so I do things like this:
      if(whereField.length > 0){
        ref = ref.where(
          whereField,
          // if the value in Map is null, is ignored by firestore `where` method
          isEqualTo:              where[FireWhere.isEqualTo],
          isGreaterThan:          where[FireWhere.isGreaterThan],
          isGreaterThanOrEqualTo: where[FireWhere.isGreaterThanOrEqualTo],
          isLessThan:             where[FireWhere.isLessThan],
          isLessThanOrEqualTo:    where[FireWhere.isLessThanOrEqualTo],
          isNotEqualTo:           where[FireWhere.isNotEqualTo],
          isNull:                 where[FireWhere.isNull],
          whereIn:                where[FireWhere.whereIn],
          whereNotIn:             where[FireWhere.whereNotIn],
          arrayContains:          where[FireWhere.arrayContains],
          arrayContainsAny:       where[FireWhere.arrayContainsAny]
        );
      }
      
      if(limit != null) ref = ref.limit(limit);

      if(orderBy != null) ref = ref.orderBy(orderBy, descending: orderDescending);
      
      QuerySnapshot data = await ref.get();
      
      // save data in a list
      data.docs.forEach((element) {
        docsList.add({
          ...element.data(),
          "id": element.id
        });
      });

      return docsList;
  }
}

main.dart

import 'package:firebase_core/firebase_core.dart';
import 'package:flutter/material.dart';
import './Firebase/database.dart';

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  
  // ========== api use ==================
  var myDocs = await FirestoreDB().getData(
    'numbers',
    whereField: 'n',
    where: { FireWhere.isLessThan: 18 },
    limit: 1
  );
  
  print(myDocs);
  // =====================================
  
  runApp(MyApp());
}


class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Text("Hi");
  }
}