是否可以在颤振中显示 TextFormField 中的外键数据

Question

我是 flutter 的新手，想创建 Category 表，其中外键是同一个表的 id 来创建子类别。我不知道如何在颤振中使用此类表创建数据。下面是我的分类模型类代码和databaseHelper类代码。

类别型号代码：

final String tableCategory = 'category';

class CategoryModel {
  final int? id;
  final String name;
  final String desc;
  final int? parentId;
  final bool isActive;
  final DateTime createdTime;
  final String createdBy;

  CategoryModel(
      {this.id,
      required this.name,
      required this.desc,
      this.parentId,
      required this.isActive,
      required this.createdTime,
      required this.createdBy});

  factory CategoryModel.fromMap(Map<String, dynamic> json) => CategoryModel(
        id: json["id"],
        name: json["name"],
        desc: json["desc"],
        parentId: json["parentId"],
        isActive: json["isActive"] == 1,
        createdTime: DateTime.parse(json["createdTime"]),
        createdBy: json["createdBy"],
      );

  Map<String, dynamic> toMap() => {
        "id": id,
        "name": name,
        "desc": desc,
        "parentId": parentId,
        "isActive": isActive ? 1 : 0,
        "createdTime": createdTime.toIso8601String(),
        "createdBy": createdBy,
      };
}

databaseHelper 类代码：

import 'package:budget_app/model/categoryModel.dart';
import 'package:sqflite/sqflite.dart';
import 'package:path/path.dart';

class DB {
  static final DB instance = DB._init();

  static Database? _database;

  DB._init();

  Future<Database> get database async{
    if(_database != null) return _database!;

    _database = await _initDB('budget.db');
    return _database!;
  }

  Future<Database> _initDB(String filePath) async {
    final dbPath = await getDatabasesPath();
    final path = join(dbPath, filePath);
    
    return await openDatabase(path, version: 1, onCreate: _onCreate, onConfigure: _onConfigure);
  }

  Future _onCreate(Database db, int version) async {
      await db.execute('''
        CREATE TABLE $tableCategory(
          id INTEGER PRIMARY KEY AUTOINCREMENT,
          name TEXT NOT NULL,
          desc TEXT NOT NULL,
          parentId INTEGER,
          FOREIGN KEY(parentId) REFERENCES $tableCategory (id) ON DELETE NO ACTION ON UPDATE NO ACTION,
          isActive BOOLEAN NOT NULL,
          createdTime DATETIME DEFAULT (cast(strftime('%s','now') as int)),
          createdBy TEXT NOT NULL,
        )
      ''');
    }

  Future _onConfigure(Database db) async {
      // Add support for cascade delete
      await db.execute("PRAGMA foreign_keys = ON");
    }

  //Custom Category Functions
  Future<bool> insertCategory(CategoryModel categoryModel) async {
    final db = await instance.database;
    db.insert("Categories", categoryModel.toMap());
    return true;
  }

  Future<List<CategoryModel>> getCategory() async {
    final db = await instance.database;
    final List<Map<String, Object?>> categories = await db.query("Categories");
    return categories.map((e) => CategoryModel.fromMap(e)).toList();
  }

  Future<int> updateCategory(CategoryModel categoryModel) async {
    final db = await instance.database;

    return db.update(
      tableCategory,
      categoryModel.toMap(),
      where: 'id = ?',
      whereArgs: [categoryModel.id],
    );
  }

  Future<int> deleteCategory(int id) async {
    final db = await instance.database;

    return await db.delete(
      tableCategory,
      where: 'id = ?',
      whereArgs: [id],
    );
  }

  Future close() async {
    final db = await instance.database;

    db.close();
  }
}