在 Flutter 中获取数据库中列数的最佳方法？

我有一个类DBHelper，我可以使用它在数据库中添加和删除数据。我遇到了这种问题，我无法获得列数。我在 Stack 上看到了同样的问题，但我不知道如何创建一个可以获取列数的类方法。他在那里以某种方式初始化了数据库，我无法理解。如果您能提供帮助，我将不胜感激）

这是那个代码

int count = Sqflite.firstIntValue(await db.rawQuery('SELECT COUNT(*) FROM table_name'));

DBHelper 代码

    import 'dart:async';
import 'dart:io' as io;

import 'package:janzer/database_model.dart';

import 'package:sqflite/sqflite.dart';
import 'package:path/path.dart';
import 'package:path_provider/path_provider.dart';

class DBHelper {
  static Database db_instance;

  final String TABLE_NAME = "DatabaseModel";

  Future<Database> get db async {
    if (db_instance == null) db_instance = await initDB();
    return db_instance;
  }

  initDB() async {
    io.Directory documentsDirectory = await getApplicationDocumentsDirectory();
    String path = join(documentsDirectory.path, "maps_database.db");
    var db = await openDatabase(path, version: 3, onCreate: onCreateFunc);
    return db;
  }


  void onCreateFunc(Database db, int version) async {
    await db.execute('CREATE TABLE $TABLE_NAME'
        '(id INTEGER PRIMARY KEY,'
        'realTime TEXT, '
        'moduleDate TEXT, '
        'moduleTime TEXT, '
        'moduleDay TEXT, '
        'gpsCoordinates TEXT, '
        'gpsSatellites TEXT, '
        'gpsTime TEXT, '
        'gpsDate TEXT, '
        'temperature TEXT, '
        'pressure TEXT, '
        'humidity TEXT, '
        'dust TEXT, '
        'zivert TEXT )');

  }

  //getData
  Future<List<DatabaseModel>> getContacts() async {
    var db_connection = await db;
    List<Map> list = await db_connection.rawQuery('SELECT * FROM $TABLE_NAME');
    List<DatabaseModel> databaseModelS = new List();
    for (int i = 0; i < list.length; i++) {
      DatabaseModel databaseModel = new DatabaseModel();
      databaseModel.id = list[i]['id'];
      databaseModel.realTime = list[i]['realTime'];
      databaseModel.moduleDate = list[i]['moduleDate'];
      databaseModel.moduleTime = list[i]['moduleTime'];
      databaseModel.moduleDay = list[i]['moduleDay'];
      databaseModel.gpsCoordinates = list[i]['systemTime'];
      databaseModel.gpsSatellites = list[i]['gpsSatellites'];
      databaseModel.gpsTime = list[i]['gpsTime'];
      databaseModel.gpsDate = list[i]['gpsDate'];
      databaseModel.temperature = list[i]['temperature'];
      databaseModel.pressure = list[i]['pressure'];
      databaseModel.humidity = list[i]['humidity'];
      databaseModel.dust = list[i]['dust'];
      databaseModel.sievert = list[i]['zivert'];

      databaseModelS.add(databaseModel);
    }
    return databaseModelS;
  }

  void addNewContact(DatabaseModel databaseModel) async {
    var db_connection = await db;
    String query = 'INSERT INTO '
        '$TABLE_NAME(realTime, '
        'moduleDate, '
        'moduleTime, '
        'moduleDay, '
        'gpsCoordinates, '
        'gpsSatellites, '
        'gpsTime, '
        'gpsDate, '
        'temperature, '
        'temperature, '
        'pressure, '
        'dust, '
        'zivert) '
        'VALUES( \'${databaseModel.realTime}\','
        '\'${databaseModel.moduleDate}\', '
        '\'${databaseModel.moduleTime}\','
        '\'${databaseModel.moduleDay}\','
        '\'${databaseModel.gpsCoordinates}\', '
        '\'${databaseModel.gpsSatellites}\','
        '\'${databaseModel.gpsTime}\','
        '\'${databaseModel.gpsDate}\','
        '\'${databaseModel.temperature}\', '
        '\'${databaseModel.pressure}\', '
        '\'${databaseModel.humidity}\','
        '\'${databaseModel.dust}\','
        '\'${databaseModel.sievert}\')';
    await db_connection.transaction((transition) async {
      return await transition.rawInsert(query);
    });
  }

  void updateContact(DatabaseModel databaseModel) async {
    var db_connection = await db;
    String query =
        'UPDATE $TABLE_NAME SET name ='
        '\'${databaseModel.realTime}\','
        '\'${databaseModel.moduleDate}\', '
        '\'${databaseModel.moduleTime}\','
        '\'${databaseModel.moduleDay}\','
        '\'${databaseModel.gpsCoordinates}\', '
        '\'${databaseModel.gpsSatellites}\','
        '\'${databaseModel.gpsTime}\','
        '\'${databaseModel.gpsDate}\','
        '\'${databaseModel.temperature}\', '
        '\'${databaseModel.pressure}\', '
        '\'${databaseModel.humidity}\','
        '\'${databaseModel.dust}\','
        '\'${databaseModel.sievert}\' WHERE id = ${databaseModel.id}';
    await db_connection.transaction((transition) async {
      return await transition.rawQuery(query);
    });
  }

  void deleteContact(DatabaseModel databaseModel) async {
    var db_connection = await db;
    String query = 'DELETE FROM $TABLE_NAME WHERE id = ${databaseModel.id}';
    await db_connection.transaction((transition) async {
      return await transition.rawQuery(query);
    });
  }
}

型号类代码

class DatabaseModel {
  DatabaseModel();

  String realTime,
      moduleDate,
      moduleTime,
      moduleDay,
      gpsCoordinates,
      gpsSatellites,
      gpsTime,
      gpsDate,
      temperature,
      pressure,
      humidity,
      dust,
      countDB,
      sievert;

  int id;
}