964927b597
* docs improvements and changes * updated module definition * modules + dml changes * fix build * fix vale error * fix lint errors * fixes to stripe docs * fix condition * fix condition * fix module defintion * fix checkout * disable UI action * change oas preview action * flatten provider module options * fix lint errors * add module link docs * pr comments fixes * fix vale error * change node engine version * links -> linkable * add note about database name * small fixes * link fixes * fix response code in api reference * added migrations step
77 lines
1.7 KiB
Plaintext
77 lines
1.7 KiB
Plaintext
export const metadata = {
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title: `${pageNumber} Loaders`,
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}
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# {metadata.title}
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In this chapter, you’ll learn about loaders and how to use them.
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## What is a Loader?
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A loader is a function executed when the Medusa application starts. You define and export it in a module.
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---
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## How to Create a Loader?
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A loader is created in a TypeScript or JavaScript file under a module's `loaders` directory.
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For example, create the file `src/modules/hello/loaders/hello-world.ts` with the following content:
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```ts title="src/modules/hello/loaders/hello-world.ts"
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export default function helloWorldLoader() {
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console.log(
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"[HELLO MODULE] Just started the Medusa application!"
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)
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}
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```
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### Export Loader in Module Definition
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Import the loader in `src/modules/hello/index.ts` and export it in the module's definition:
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```ts title="src/modules/hello/index.ts"
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// other imports...
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import helloWorldLoader from "./loaders/hello-world"
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export default Module("hello", {
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// ...
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loaders: [helloWorldLoader],
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})
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```
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The value of the `loaders` property is an array of loader functions.
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---
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## Test the Loader
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Start the Medusa application:
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```bash npm2yarn
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npm run dev
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```
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Among the messages logged in the terminal, you’ll see the following message:
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```bash
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[HELLO MODULE] Just started the Medusa application!
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```
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---
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## When to Use Loaders
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<Note title="Use loaders when" type="success">
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- You're performing an action at application start-up.
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- You're establishing a one-time connection with an external system.
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</Note>
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<Note title="Don't use loaders if" type="error">
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- You want to perform an action continuously or at a set time pattern in the application. Use scheduled jobs instead, which is explained in an upcoming chapter.
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</Note>
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