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feat(example-context): add sync-async example to resolve bindings
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,80 @@ | ||
| // Copyright IBM Corp. 2019. All Rights Reserved. | ||
| // Node module: @loopback/example-context | ||
| // This file is licensed under the MIT License. | ||
| // License text available at https://opensource.org/licenses/MIT | ||
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| import {BindingKey, Context, inject} from '@loopback/context'; | ||
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| const CURRENT_USER = BindingKey.create<string>('currentUser'); | ||
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| /** | ||
| * A class with dependency injection | ||
| */ | ||
| class Greeter { | ||
| /** | ||
| * The dependency of current user can be sync or async depending on the | ||
| * value for `CURRENT_USER` binding. | ||
| * @param userName - User name | ||
| */ | ||
| constructor(@inject(CURRENT_USER) private userName: string) {} | ||
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| hello() { | ||
| return `Hello, ${this.userName}`; | ||
| } | ||
| } | ||
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| /** | ||
| * A strongly-typed binding key for `Greeter` | ||
| */ | ||
| const GREETER = BindingKey.create<Greeter>('greeter'); | ||
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| async function greetWithSyncUser(ctx: Context) { | ||
| // Set the current user to `John` (a constant value) | ||
| // As a result, CURRENT_USER can be resolved synchronously | ||
| ctx.bind(CURRENT_USER).to('John (sync)'); | ||
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| // Greeter has a dependency on current user which can be resolved | ||
| // synchronously. This allows GREETER to be resolved either synchronously or | ||
| // asynchronously. | ||
| // Get an instance of Greeter synchronously | ||
| let greeter = ctx.getSync(GREETER); | ||
| console.log('%s', greeter.hello()); | ||
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| // Get an instance of Greeter asynchronously | ||
| greeter = await ctx.get(GREETER); | ||
| console.log('%s', greeter.hello()); | ||
| return greeter; | ||
| } | ||
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| async function greetWithAsyncUser(ctx: Context) { | ||
| // Now set the current user to an async factory | ||
| // As a result, CURRENT_USER can only be resolved asynchronously | ||
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| ctx.bind(CURRENT_USER).toDynamicValue(() => Promise.resolve('Jane (async)')); | ||
| // Get an instance of Greeter asynchronously | ||
| let greeter = await ctx.get(GREETER); | ||
| console.log('%s', greeter.hello()); | ||
| try { | ||
| // Get an instance of Greeter synchronously - THIS WILL FAIL | ||
| greeter = ctx.getSync(GREETER); | ||
| console.log(greeter.hello()); | ||
| } catch (err) { | ||
| // Error: Cannot get greeter synchronously: the value is a promise | ||
| console.log('Expect to fail with error: %s', err.message); | ||
| } | ||
| } | ||
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| export async function main() { | ||
| const ctx = new Context('request'); | ||
| // Bind `GREETER` to a class from which the value is instantiated | ||
| ctx.bind(GREETER).toClass(Greeter); | ||
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| // Now try to invoke a greeter with synchronous resolution of the current user | ||
| await greetWithSyncUser(ctx); | ||
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| // Then try to invoke a greeter with asynchronous resolution of the current user | ||
| await greetWithAsyncUser(ctx); | ||
| } | ||
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| // tslint:disable-next-line:no-floating-promises | ||
| if (require.main === module) main(); |