Data in SQLflite database is not deleting, in my Flutter project - flutter

Question

So I have an issue of data not being deleted from my database. It is supposed to happen when a dismissible widget is swiped away.
This is the model class:
class DateModel {
//define schema
int? id;
final String dateText;
DateModel({this.id, required this.dateText});
//convert json data to DateModel instance
factory DateModel.fromMap(Map<String, dynamic> json) {
return DateModel(id: json["id"], dateText: json["dateText"]);
}
//convert DateModel instance to json
Map<String, dynamic> toMap() => {"id": id, "dateText": dateText};
}
Below is where some CRUD operations are defined. I concluded that the error is because I'm not properly storing the id upon insert (in the "add" function). Although I'm not certain I'm doing this right.
class DatabaseHelper {
static Database? _db;
//create singleton
DatabaseHelper._constructor();
static final DatabaseHelper instance = DatabaseHelper._constructor();
Future<Database> get db async {
return _db ??= await init_db("Date.db");
}
//create database when it doesn't exist
Future<Database> init_db(String name) async {
//locate database
var databasePath = await getDatabasesPath();
String path = join(databasePath, name);
//open database and return
return await openDatabase(path, version: 1, onCreate: _onCreate);
}
//Create date table
Future _onCreate(Database db, int version) async {
await db
.execute("CREATE TABLE Dates (id INTEGER PRIMARY KEY, dateText TEXT)");
}
//add user input to table
Future<int> add(DateModel dateModel) async {
Database db = await instance.db;
//store id of inserted date (generated by db.insert method)
final id = await db.insert("Dates", dateModel.toMap());
return dateModel.id = id;
}
//remove date from table
Future<int> remove(int id) async {
Database db = await instance.db;
return await db.delete("Dates", where: "id = ?", whereArgs: [id]);
}
Future<List> getDates() async {
Database db = await instance.db;
final data = await db.rawQuery("SELECT dateText FROM Dates");
if (data.isNotEmpty) {
return data;
} else {
return [];
}
}
}
And lastly, this is where the delete action is supposed to take place (in dismissible's onDismissed property):
Widget build(BuildContext context) {
return Consumer<Date>(builder: (context, date, child) {
return Scaffold(
body: FutureBuilder(
future: DatabaseHelper.instance.getDates(),
builder: (context, AsyncSnapshot<List<dynamic>> snapshot) {
if (!snapshot.hasData || snapshot.connectionState != ConnectionState.done) {
return CircularProgressIndicator();
}
return ListView.builder(
shrinkWrap: true,
itemCount: snapshot.data!.length,
itemBuilder: (context, index) {
return SlideTransition(
position:
Tween<Offset>(begin: Offset(1, 0), end: Offset(0, 0))
.animate(CurvedAnimation(
parent: _controller, curve: Curves.bounceIn)),
child: Dismissible(
key: UniqueKey(),
direction: DismissDirection.horizontal,
onDismissed: (direction) async {
final dateModel =
DateModel(dateText: date.dateList[index]);
//remove from list
date.dateList.removeAt(index);
//remove from database
await DatabaseHelper.instance.remove(dateModel.id!);
},
child: ListTile(title: Text(snapshot.data![index].toString()))),
);
});
},
),
);
});
}
I get the error that I'm doing a null check on a null value, which I believe is the dateModel.id.
I tried storing the id upon insert a couple of different ways. Nothing changed.

Answer 1

This is because you are trying to do exactly that: Putting a null check operator on a null value.
You are creating the dateModel like this:
final dateModel = DateModel(dateText: date.dateList[index]);
You do not pass any value for the id, which then is null.
Try something like this:
Map<String, dynamic> dateJson = snapshot.data![index] as Map<String, dynamic>;
DateModel dateModel = DateModel.fromMap(dateJson);
date.dateList.removeAt(index);
await DatabaseHelper.instance.remove(dateModel.id);
PS: You should not make the id optional in your DateModel class since this should always be given.