Undefined is not an object using react native realm - react-native

Question

I want to build an application using react native and implement realm. It is meant to have some playlists and songs, and the songs should be able to be added to the playlists.
Playlist:
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[]',
},
};
}
Song:
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',
},
};
}
Realm:
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;
I always get the error:
TypeError: undefined is not an object (evaluating '_playlist.Playlist.schema')
And I can't figure out why. If you need more code, just tell me.
I am new to react native and JavaScript and TypeScript. I am used to developing Android apps using Java, so maybe I did some dumb mistakes, I don't know.

Answer 1

You are not using your real instance in initData, you need to use realm.write like in the below example. I think my little piece of code should works update me what u got(its better to use Realm async than sync as you want)
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
In your case
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
});