未定义不是使用反应原生领域的对象答案

【问题标题】：Undefined is not an object using react native realm未定义不是使用反应原生领域的对象
【发布时间】：2020-05-11 18:38:19
【问题描述】：

我想使用react native 构建一个应用程序并实现realm。本来就是有一些播放列表和歌曲的，歌曲应该可以添加到播放列表中。

播放列表：

export class Playlist {
  public id: number;
  public name: string;
  public color: string;
  public songs: Song[];
  constructor(id: number, name: string, color: string, songs: Song[]) {
    this.id = id;
    this.name = name;
    this.color = color;
    this.songs = songs;
  }

  static schema: Realm.ObjectSchema = {
    name: 'Playlist',
    primaryKey: 'id',
    properties: {
      id: 'int',
      name: 'string',
      color: 'string',
      songs: 'Song[]',
    },
  };
}

歌曲：

export class Song {
  public id: number;
  public title: string;
  public artist: string;
  constructor(id: number, title: string, artist: string) {
    this.id = id;
    this.title = title;
    this.artist = artist;
  }

  static schema: Realm.ObjectSchema = {
    name: 'Song',
    primaryKey: 'id',
    properties: {
      id: 'int',
      title: 'string',
      artist: 'string',
    },
  };
}

领域：

const initData = () => {
  const songs = [
    new Song(0, 'Avicii', 'Heaven'),
    // some songs
  ];

  const playlists = [
    new Playlist(0, 'Favorite Songs', 'purple', []),
    // some playlists
  ];

  songs.forEach(song => {
    Song.insertSong(song);
  });

  playlists.forEach(playlist => {
    Playlist.insertPlaylist(playlist);
  });
};

const databaseOptions = {
  path: 'playlists.realm',
  schema: [Playlist.schema, Song.schema],
};
let realmInstance: Realm | null;
const getRealm = (): Realm => {
  if (realmInstance == null) {
    realmInstance = new Realm(databaseOptions);
    initData();
  }
  return realmInstance!;
};

export default getRealm;

我总是得到错误：

TypeError: undefined is not an object (evaluating '_playlist.Playlist.schema')

我不知道为什么。如果您需要更多代码，请告诉我。我是 react native 和 JavaScript 和 TypeScript 的新手。我习惯使用 Java 开发 Android 应用，所以也许我犯了一些愚蠢的错误，我不知道。

【问题讨论】：

标签： react-native realm

【解决方案1】：

你没有在 initData 中使用你的真实实例，你需要像下面的例子一样使用 realm.write。我认为我的一小段代码应该可以更新我得到的信息（使用 Realm 异步比使用同步更好）

const PersonSchema = {
  name: 'Person',
  properties: {
    // The following property definitions are equivalent
    cars: {type: 'list', objectType: 'Car'},
    vans: 'Car[]'
  }
}

let carList = person.cars;

// Add new cars to the list
realm.write(() => {
  carList.push({make: 'Honda', model: 'Accord', miles: 100});
  carList.push({make: 'Toyota', model: 'Prius', miles: 200});
});

let secondCar = carList[1].model;  // access using an array index

你的情况

Realm.open({schema: [Song, PlayList]})
  .then(realm => {
    // ...use the realm instance here
   try {
      realm.write(() => {
         const songs = [
            realm.create('Song',{title: 'Avicii', artist: 'Heaven'}),
         ];

         const playlists = [
           realm.create('Playlist',{name: 'Favorite Songs', color: 'purple', songs: []}),
           // some playlists
         ];
         playlists.forEach(playlist => {
           for (const song of songs){
               playlist.songs.push(song);
            }
         });
      });
   } catch (e) {
     console.log("Error on creation");
   }
  })
  .catch(error => {
    // Handle the error here if something went wrong
  });

【讨论】：