Assign sqlite query result to Flutter variable

Question

My app requires employees to scan an NFC tag to clock in and out for work. What I want to achieve is to prevent duplicate entries - i.e. before an someone can clock in again, they have to be clocked out. The result is displayed in a snackbar.

Code for my conditional statement (in attendance.dart file):

var dataCheck = _query(tagIdentifier!);
if (dataCheck == 'Clock in') {
    snackbarText = 'Already clocked in';
} else {
    await addAttendanceData(
        tStamp!,
        scanDate!,
        tagText!,
        tagIdentifier,
        tagAction,
        workerText!,
        attendanceFlag);
    data = await ProjectDatabase.instance.attendanceReadAllData();
}

The _query code (in attendance.dart file):

_query(action) async {
  duplicateCheck.add(Data.attendanceFromJson(action));
}

Then the code in the helper class (separate file).

Future<Data> readAttendanceData(String id) async {
    final db = await instance.database;
    final maps = await db.query(
      attendanceDataTable,
      columns: AttendanceDataFields.values,
      where: 'tag_id = ?',
      whereArgs: [id],
    );

    if (maps.isNotEmpty) {
      return Data.attendanceFromJson(maps.first);
    } else {
      throw Exception('ID $id not found');
    }
  }

I have tried solving this issue by printing the dataCheck variable and got

Instance of 'Future'

Followed by the error:

type 'String' is not a subtype of type 'Map<String, Object?>'

My code structure was gathered from Johannes Milke's tutorial on the sqflite package in his note app example.

Any help will be greatly appreciated.