Is there a way to get a list of strings from drift in flutter

Question

I'm using Drift to manage databases in my flutter app and I need to get a list from a database. When I call for a list it just returns something called a "Instance of '_MappedSelectable<QueryRow, String>'"

This is the SQL command that returns this getAllNicks: SELECT nickname FROM car_entries;

I've tried to convert it to a list a few ways but they all just turn up in errors. Here is one way i tried (DIDN'T WORK)

List<String> convertInstanceToList(instance) {
  Map<String, dynamic> map = Map.from(instance);
  List<String> stringList = map.values.toList().cast<String>();
  return stringList;
  }

I was hoping this would convert it to a map and then turn that into a usable list but I just get this error.

Class '_MappedSelectable<QueryRow, String>' has no instance method 'toList'.
Receiver: Instance of '_MappedSelectable<QueryRow, String>'
Tried calling: toList()

Anyone got anything that might work?

Answer 1

You need a Converter:

import 'dart:convert';

import 'package:drift/drift.dart';

class StringListTypeConverter extends TypeConverter<List<String>, String> {
  @override
  List<String> fromSql(String fromDb) {
    return List<String>.from(json.decode(fromDb));
  }

  @override
  String toSql(List<String> value) {
    return json.encode(value);
  }
}

And you can use this converter in your table definition:

@drift.UseRowClass(MyCustomRowClass, generateInsertable: true)
class CommandsExecute extends Table{
  .
  .
  .
  drift.TextColumn get myStringList => text().map(StringListTypeConverter())();
}

And a custom model:

JsonSerializable()
class MyCustoRowClass extends Insertable<AssemblyMember> {
List<String> myStringList;
MyCustomRowClass({required this.myStringList});

.
.
.
//fromJson and toColumns methods
}

In this way you will be able to use a String list anywhere in your code:

List<String> myList = myCustomRowClass.myStringList;

I hope this can help you.