Storage

Back your stores with localStorage, sessionStorage or any other mechanism you wish.
Installation
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npm install @ngxs/storage-plugin --save
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​
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# or if you are using yarn
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yarn add @ngxs/storage-plugin
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Usage
Import the NgxsStoragePluginModule into your app module like:
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import { NgxsModule } from '@ngxs/store';
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import { NgxsStoragePluginModule } from '@ngxs/storage-plugin';
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​
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@NgModule({
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  imports: [NgxsModule.forRoot([]), NgxsStoragePluginModule.forRoot()]
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})
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export class AppModule {}
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It is recommended to register the storage plugin before other plugins so initial state can be picked up by those plugins.
Options
The plugin has the following optional values:
key: State name(s) to be persisted. You can pass a string or array of strings that can be deeply nested via dot notation. If not provided, it defaults to all states using the @@STATE key.
storage: Storage strategy to use. This defaults to LocalStorage but you can pass SessionStorage or anything that implements the StorageEngine API.
deserialize: Custom deserializer. Defaults to JSON.parse
serialize: Custom serializer. Defaults to JSON.stringify
migrations: Migration strategies
beforeSerialize: Interceptor executed before serialization
afterDeserialize: Interceptor executed after deserialization
Key option
The key option is used to determine what states should be persisted in the storage. key shouldn't be a random string, it has to coincide with your state names. Let's look at the below example:
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// novels.state.ts
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@State<Novel[]>({
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  name: 'novels',
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  defaults: []
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})
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@Injectable()
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export class NovelsState {}
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​
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// detectives.state.ts
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@State<Detective[]>({
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  name: 'detectives',
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  defaults: []
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})
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@Injectable()
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export class DetectivesState {}
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In order to persist all states there is no need to provide the key option, so it's enough just to write:
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@NgModule({
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  imports: [NgxsStoragePluginModule.forRoot()]
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})
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export class AppModule {}
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But what if we wanted to persist only NovelsState? Then we would have needed to pass its name to the key option:
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@NgModule({
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  imports: [
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    NgxsStoragePluginModule.forRoot({
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      key: 'novels'
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    })
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  ]
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})
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export class AppModule {}
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It's also possible to provide a state class as opposed to its name:
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@NgModule({
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  imports: [
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    NgxsStoragePluginModule.forRoot({
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      key: NovelsState
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    })
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  ]
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})
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export class AppModule {}
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And if we wanted to persist NovelsState and DetectivesState:
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@NgModule({
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  imports: [
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    NgxsStoragePluginModule.forRoot({
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      key: ['novels', 'detectives']
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    })
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  ]
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})
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export class AppModule {}
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Or using state classes:
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@NgModule({
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  imports: [
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    NgxsStoragePluginModule.forRoot({
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      key: [NovelsState, DetectivesState]
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    })
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  ]
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})
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export class AppModule {}
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You can even combine state classes and strings:
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@NgModule({
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  imports: [
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    NgxsStoragePluginModule.forRoot({
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      key: ['novels', DetectivesState]
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    })
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  ]
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})
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export class AppModule {}
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This is very handy to avoid persisting runtime-only states that shouldn't be saved to any storage.
Custom Storage Engine
You can add your own storage engine by implementing the StorageEngine interface.
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import { NgxsStoragePluginModule, StorageEngine, STORAGE_ENGINE } from '@ngxs/storage-plugin';
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​
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export class MyStorageEngine implements StorageEngine {
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  get length(): number {
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    // Your logic here
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  }
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​
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  getItem(key: string): any {
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    // Your logic here
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  }
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​
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  setItem(key: string, val: any): void {
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    // Your logic here
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  }
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​
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  removeItem(key: string): void {
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    // Your logic here
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  }
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​
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  clear(): void {
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    // Your logic here
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  }
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​
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  key(val: number): string {
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    // Your logic here
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  }
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}
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​
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@NgModule({
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  imports: [NgxsModule.forRoot([]), NgxsStoragePluginModule.forRoot()],
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  providers: [
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    {
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      provide: STORAGE_ENGINE,
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      useClass: MyStorageEngine
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    }
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  ]
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})
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export class MyModule {}
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Serialization Interceptors
You can define your own logic before or after the state get serialized or deserialized.
beforeSerialize: Use this option to alter the state before it gets serialized.
afterSerialize: Use this option to alter the state after it gets deserialized. For instance, you can use it to instantiate a concrete class.
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@NgModule({
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  imports: [
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    NgxsStoragePluginModule.forRoot({
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      key: 'counter',
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      beforeSerialize: (obj, key) => {
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        if (key === 'counter') {
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          return {
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            count: obj.count < 10 ? obj.count : 10
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          };
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        }
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        return obj;
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      },
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      afterDeserialize: (obj, key) => {
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        if (key === 'counter') {
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          return new CounterInfoStateModel(obj.count);
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        }
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        return obj;
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      }
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    })
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  ]
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})
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export class AppModule {}
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Migrations
You can migrate data from one version to another during the startup of the store. Below is a strategy to migrate my state from animals to newAnimals.
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@NgModule({
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  imports: [
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    NgxsModule.forRoot([]),
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    NgxsStoragePluginModule.forRoot({
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      migrations: [
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        {
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          version: 1,
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          key: 'zoo',
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          versionKey: 'myVersion',
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          migrate: state => {
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            return {
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              newAnimals: state.animals,
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              version: 2 // Important to set this to the next version!
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            };
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          }
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        }
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      ]
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    })
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  ]
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})
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export class MyModule {}
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In the migration strategy, we define:
version: The version we are migrating
versionKey: The identifier for the version key (Defaults to 'version')
migrate: A function that accepts a state and expects the new state in return.
key: The key for the item to migrate. If not specified, it takes the entire storage state.
Note: Its important to specify the strategies in the order of which they should progress.
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Last modified 2yr ago
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Contents
Custom Storage Engine
Serialization Interceptors
Migrations