FLUTTER，SQFLITE，如果相关数据仍然存在，如何防止删除？

Question

嗨，伙计们，我是Flutter的新手，现在有实习生。

所以我在这里有3个表，它们是项目数据库是主要的，组数据库，类别数据库。

如果项目数据库正在使用该组，我应该如何防止用户删除组数据库，因为该组已在项目数据库中使用？

如果有人能指导我，那就太好了，因为我对此完全陌生，而且因为实习生的关系，我必须尽快完成它。

 import 'dart:async';
import 'dart:io' as io;
import 'package:path/path.dart';
import 'package:sqflite/sqflite.dart';
import 'package:path_provider/path_provider.dart';
import 'package:ezystock/model/item_model.dart';
import 'package:ezystock/model/group_model.dart';
import 'package:ezystock/model/category_model.dart';

class DBHelper {
  static Database _db;
  static const String DB_NAME = 'database.db';

  Future<Database> get db async {
    if (_db != null) {
      return _db;
    }
    _db = await initDb();
    return _db;
  }

  initDb() async {
    io.Directory documentsDirectory = await getApplicationDocumentsDirectory();
    String path = join(documentsDirectory.path, DB_NAME);
    var db = await openDatabase(path, version: 1, onCreate: _onCreate);
    return db;
  }

  _onCreate(Database db, int version) async {
    await db.execute("CREATE TABLE 'item' ('id' INTEGER PRIMARY KEY, 'code' TEXT, 'description' TEXT,'cost' REAL,'price' REAL,'category' TEXT,'group' TEXT)");
    await db.execute("CREATE TABLE 'group' ('id' INTEGER PRIMARY KEY, 'code' TEXT, 'description' TEXT)");
    await db.execute("CREATE TABLE 'category' ('id' INTEGER PRIMARY KEY, 'code' TEXT, 'description' TEXT)");
  }

//Category
  Future<Category> saveCategory(Category category) async {
    var dbClient = await db;
    category.id = await dbClient.insert("category", category.toMap());
    return category;
  }

  Future<List<Category>> getCategory() async {
    var dbClient = await db;
    List<Map> maps = await dbClient.query("category", columns: ["id", "code","description"]);
    //List<Map> maps = await dbClient.rawQuery("SELECT * FROM $TABLE");
    List<Category> category = [];
    if (maps.length > 0) {
      for (int i = 0; i < maps.length; i++) {
        category.add(Category.fromMap(maps[i]));
      }
    }
    return category;
  }

  Future<int> deleteCategory(int id) async {
    var dbClient = await db;
    return await dbClient.delete("category", where: 'id = ?', whereArgs: [id]);
  }

  Future<int> updateCategory(Category category) async {
    var dbClient = await db;
    return await dbClient.update("category", category.toMap(),
        where: 'id = ?', whereArgs: [category.id]);
  }


  //Group
  Future<Group> saveGroups(Group group) async {
    var dbClient = await db;
    group.id = await dbClient.insert("group", group.toMap());
    return group;
  }

  Future<List<Group>> getGroups() async {
    var dbClient = await db;
    List<Map> maps = await dbClient.query("group", columns: ["id", "code","description"]);
    //List<Map> maps = await dbClient.rawQuery("SELECT * FROM $TABLE");
    List<Group> groups = [];
    if (maps.length > 0) {
      for (int i = 0; i < maps.length; i++) {
        groups.add(Group.fromMap(maps[i]));
      }
    }
    return groups;
  }

  Future<int> deleteGroups(int id) async {
    var dbClient = await db;
    List<Map> items = await dbClient.query("item", where: 'group = ?', whereArgs: [id]);
    if (items.length > 0) {
      return await dbClient.delete("group", where: 'id = ?', whereArgs: [id]);
    } else {

    }
  }

  Future<int> updateGroups(Group group) async {
    var dbClient = await db;
    return await dbClient.update("group", group.toMap(),
        where: 'id = ?', whereArgs: [group.id]);
  }




  //items
  Future<Items> saveItems(Items items) async {
    var dbClient = await db;
    items.id = await dbClient.insert("item", items.toMap());
    return items;
  }

  Future<List<Items>> getItems() async {
    var dbClient = await db;
    List<Map> maps = await dbClient.query("item", columns: ["id", "code","description","cost","price","category","group"]);
    //List<Map> maps = await dbClient.rawQuery("SELECT * FROM $TABLE");
    List<Items> groups = [];
    if (maps.length > 0) {
      for (int i = 0; i < maps.length; i++) {
        groups.add(Items.fromMap(maps[i]));
      }
    }
    return groups;
  }

  Future<int> deleteItems(int id) async {
    var dbClient = await db;
    return await dbClient.delete("item", where: 'id = ?', whereArgs: [id]);
  }

  Future<int> updateItems(Items items) async {
    var dbClient = await db;
    return await dbClient.update("item", items.toMap(),
        where: 'id = ?', whereArgs: [items.id]);
  }

  Future close() async {
    var dbClient = await db;
    dbClient.close();
  }
}

Answer 1

答案是:不提供任何方法来删除group表。所以删除下面的代码：

  Future<int> deleteGroups(int id) async {
    var dbClient = await db;
    List<Map> items = await dbClient.query("item", where: 'group = ?', whereArgs: [id]);
    if (items.length > 0) {
      return await dbClient.delete("group", where: 'id = ?', whereArgs: [id]);
    } else {

    }