Import csv to sqlite in Flutter (insert issue) - sqlite

Question

I've already read the related article and solution + mentioned method, but still I don't get it what should I add to my code for importing csv to sqlite table List<<Map<String, dynamic>. I need to replace existing table with a new one and insert each lines of converted csv. How can I solve it? Here's my code below.The problem is importVoca() of db.dart.
db.dart
class DBHelper {
var _db;
// create database
Future<Database> get database async {
if (_db != null) return _db;
_db = openDatabase(
join(await getDatabasesPath(), 'vocas.db'),
onCreate: (db, version) {
return db.execute(
"CREATE TABLE vocas(id TEXT PRIMARY KEY, word TEXT, meaning TEXT, createTime TEXT)",
);
},
version: 1,
);
return _db;
}
// insert voca
Future<void> insertVoca(Voca voca) async {
final db = await database;
await db.insert('vocas', voca.toMap(),
conflictAlgorithm: ConflictAlgorithm.replace);
}
// Voca list
Future<List<Voca>> vocas() async {
final db = await database;
final List<Map<String, dynamic>> maps = await db.query('vocas');
return List.generate(maps.length, (i) {
return Voca(
id: maps[i]['id'],
word: maps[i]['word'],
meaning: maps[i]['meaning'],
createTime: maps[i]['createTime']);
});
}
//update voca list
Future<void> updateVoca(Voca voca) async {
final db = await database;
await db.update(
'vocas',
voca.toMap(),
where: "id = ?",
whereArgs: [voca.id],
);
}
//delete voca
Future<void> deleteVoca(String id) async {
final db = await database;
await db.delete(
'vocas',
where: "id = ?",
whereArgs: [id],
);
}
//find voca to edit
Future<List<Voca>> findVoca(String id) async {
final db = await database;
final List<Map<String, dynamic>> maps =
await db.query('vocas', where: 'id = ?', whereArgs: [id]);
return List.generate(maps.length, (i) {
return Voca(
id: maps[i]['id'],
word: maps[i]['word'],
meaning: maps[i]['meaning'],
createTime: maps[i]['createTime'],
);
});
}
//export voca to csv
Future exportVoca() async {
var year = DateFormat('yy').format(DateTime.now());
var month = DateFormat('MM').format(DateTime.now());
var day = DateFormat('d').format(DateTime.now());
final db = await database;
var result = await db.query('vocas');
var csv = mapListToCsv(result);
final directory = await getApplicationDocumentsDirectory();
final pathOfFile = await directory.path;
File file = File("$pathOfFile/dontForget_$year$month$day.csv");
file.writeAsString(csv);
}
//import csv to sqlite
Future importVoca() async {
File file = await FilePicker.getFile(
type: FileType.custom, allowedExtensions: ['csv']);
final data = file.openRead();
final fields = await data
.transform(utf8.decoder)
.transform(new CsvToListConverter())
.toList();
Database _db = await openDatabase(
join(await getDatabasesPath(), 'vocas.db'),
version: 1, onCreate: (Database db, int version) async {
await db.execute("DROP TABLE IF EXISTS vocas");
await db.execute(
"CREATE TABLE vocas(id TEXT PRIMARY KEY, word TEXT, meaning TEXT, createTime TEXT)");
});
}
}