How to insert POJO Objects and Lists in SQFlite - sqlite

Question

I am trying to store data from an API to sqflite , but I have to insert the Objects and the Lists, however during the process, am getting this error :
ERROR:flutter/lib/ui/ui_dart_state.cc(157)] Unhandled Exception: DatabaseException(java.lang.String cannot be cast to java.lang.Integer) sql 'INSERT INTO articleTable (id, created_on, title, summary, details, tags, featured_image, author, category) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)' args [21, 2020-04-14 04:04:57, Singer Jose ...}]
This is the Model Article class :
#JsonSerializable(explicitToJson: true)
class Article {
Article(this.id, this.created_on, this.title, this.details,
this.featured_image, this.author, this.category, this.summary, this.tags);
int id;
String created_on;
String title;
String summary;
String details;
List<String> tags;
String featured_image;
Author author;
Category category;
factory Article.fromJson(Map<String, dynamic> json) =>
_$ArticleFromJson(json);
Map<String, dynamic> toJson() => _$ArticleToJson(this);
}
The automated generated file for Article model class :
/ GENERATED CODE - DO NOT MODIFY BY HAND
part of 'article.dart';
// **************************************************************************
// JsonSerializableGenerator
// **************************************************************************
Article _$ArticleFromJson(Map<String, dynamic> json) {
return Article(
json['id'] as int,
json['created_on'] as String,
json['title'] as String,
json['details'] as String,
json['featured_image'] as String,
json['author'] == null
? null
: Author.fromJson(json['author'] as Map<String, dynamic>),
json['category'] == null
? null
: Category.fromJson(json['category'] as Map<String, dynamic>),
json['summary'] as String,
(json['tags'] as List)?.map((e) => e as String)?.toList(),
);
}
Map<String, dynamic> _$ArticleToJson(Article instance) => <String, dynamic>{
'id': instance.id,
'created_on': instance.created_on,
'title': instance.title,
'summary': instance.summary,
'details': instance.details,
'tags': instance.tags,
'featured_image': instance.featured_image,
'author': instance.author?.toJson(),
'category': instance.category?.toJson(),
};
This is where am doing my Sqflite insertion :
class ArticleApiProvider {
Future<List<Article>> fetchArticles() async {
final response =
await http.get('https://api.xyxyxyxy');
if (response.statusCode == 200) {
List jsonResponse = jsonDecode(response.body);
return jsonResponse.map((article) {
articleBloc.addArticles(Article.fromJson(article));
}).toList();
} else {
throw Exception('Failed to retrieve articles');
}
}
}
My Bloc Class :
class ArticleBloc {
final _repository = Repository();
final _articleFetcher = PublishSubject<List<Article>>();
Stream<List<Article>> get allArticles => _articleFetcher.stream;
fetchArticles() async {
List<Article> articles = await _repository.fetchArticles();
_articleFetcher.sink.add(articles);
}
getArticlesCached() async {
// sink is a way of adding data reactively to the stream
// by registering a new event
_articleFetcher.sink.add(await _repository.getAllArticles());
}
void addArticles(Article article) async {
await _repository.insertArticle(article);
}
dispose() {
_articleFetcher.close();
}
}
final articleBloc = ArticleBloc();
This is the DatabaseProvider class
final articlesTable = "articleTable";
class DatabaseProvider {
static final DatabaseProvider dbProvider = DatabaseProvider();
Database _database;
String id = "id";
String createdOn = "created_on";
String title = "title";
String summary = "summary";
String details = "details";
String featuredImage = "featured_image";
String author = "author";
String category = "category";
String tags = "tags";
Future<Database> get database async {
if (_database != null) return _database;
_database = await createDatabase();
return _database;
}
createDatabase() async {
Directory documentsDirectory = await getApplicationDocumentsDirectory();
// NewVision.db is our database instance name
String path = join(documentsDirectory.path, "NewVision.db");
var database = await openDatabase(path,
version: 1, onCreate: initDB, onUpgrade: onUpgrade);
return database;
}
void initDB(Database db, int version) async {
await db.execute(
'CREATE TABLE $articlesTable($id INTEGER PRIMARY KEY AUTOINCREMENT, $createdOn TEXT, $title TEXT ,'
' $summary TEXT , $details TEXT , '
'$tags TEXT, $featuredImage TEXT , $author TEXT , $category TEXT )');
}
void onUpgrade(Database db, int oldVersion, int newVersion) {
if (newVersion > oldVersion) {}
}
}
String join(String path, String s) {
return path + s;
}
The rest of the files do follow the Bloc architecture, for the purposes of making the question precise, I think form what I have provided, I can get some help.
I will be grateful for your help.

Answer 1

Thanks for the detailed report. My assumption is that the error comes from your tags property. List of String is not a supported type in SQLite. sqflite supports List of int for compatibility reason (for blobs but Uint8List will likely be the only supported type in the future) so the casting error could come from this.
You should try to encode your tags (json or comma separated string) before doing another investigation.
This issue also applies to the author and category fields.
You have to flatten your model. See the supported types help section: https://github.com/tekartik/sqflite/blob/master/sqflite/doc/supported_types.md
Basically int, double, String and Uint8List(blob) are the only types supported. Unfortunately you have to convert your inner List and Map, json being one solution.
But i agree the error reported does not help in finding the issue, that could definitely be improved...