Saving List<String> in flutter using Drift database

Question

I need to store a list of strings inside drift database , i have actually set up a typeconverter to do that but i'm not sure exactly how to pass , i would appreciate anyone help , Thank you in advance.

• This is database table ( class called movies.drift )

 
CREATE TABLE movie (
    id INT NOT NULL PRIMARY KEY AUTOINCREMENT,
    title TEXT,
    language TEXT,
    voteAverage TEXT,
    overView TEXT,
    releaseDate TEXT,
    movieImageUrl TEXT,
);

• This is my drift helper class

 @DriftDatabase(include : {'movies.drift'})
class MovieDatabase extends _$MovieDatabase {
  MovieDatabase() : super(_openConnection());

  @override
  int get schemaVersion => 1;

  Future<List<MovieData>> getMovies() async {
    return await select(movie).get();
  }
  Future<int> saveMovie(MovieCompanion companion) async {
    return await into(movie).insert(companion);
  }
  // Future<int> deleteMovie(int id) async {
  //   return (delete(movie)..where(movie.id.equals(id))).go();
  // }
  Future<int> deleteAllMovies() async {
    return await delete(movie).go();
  }
  Future<int> updateMovie(MovieCompanion companion) async {
    return await update(movie).write(MovieCompanion(
        title: Value(companion.title.toString())
    ));
  }
}

LazyDatabase _openConnection(){
  return LazyDatabase(() async {
    final dbFolder = await getApplicationDocumentsDirectory();
    final file = File(p.join(dbFolder.path, 'movies.db'));
    return NativeDatabase(file);
  });
}

• This is my type converter

class MovieTypeConverter extends TypeConverter<List<String>,String> {
  const MovieTypeConverter();

  @override
  List<String>? mapToDart(String? fromDb) {
    if (fromDb == null) return null;
    final data = json.decode(fromDb);
    return data;
  }

  @override
  String? mapToSql(List<String>? value) {
    if (value == null) return null;
    return json.encode(value);
  }
  
}

PS : I want to basically add List to my table and use typeconverter to save it into database and then retreive it .

Answer 1

Take a look at the docs on how to use them: https://drift.simonbinder.eu/docs/advanced-features/type_converters/

Example:

Type converters can also be used inside drift files. Assuming that the Preferences and PreferenceConverter are contained in preferences.dart, that file can imported into drift for the type converter to be available.

import 'preferences.dart';

CREATE TABLE users (
  id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
  name TEXT,
  preferences TEXT MAPPED BY `const PreferenceConverter()`
);

EDIT:

Your TypeConverter should have a fromSql and toSql method.

import 'dart:convert';
import 'package:drift/drift.dart';

class MovieTypeConverter extends TypeConverter<List<String>?,String?> {
  const MovieTypeConverter();

  @override
  List<String>? fromSql(String? fromDb) {
    if (fromDb == null) return null;
    return json.decode(fromDb);
  }

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

Your drift file:

CREATE TABLE movie (
    id INT NOT NULL PRIMARY KEY AUTOINCREMENT,
    title TEXT,
    language TEXT,
    voteAverage TEXT,
    overView TEXT,
    releaseDate TEXT,
    movieImageUrl TEXT,
    movieTypes TEXT MAPPED BY `const MovieTypeConverter()`
);