69 lines
2.2 KiB
Plaintext
69 lines
2.2 KiB
Plaintext
---
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description: "Learn what loaders are in Medusa. A loader is a script that runs when the Medusa backend starts."
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---
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import DocCard from '@theme/DocCard';
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import Icons from '@theme/Icon';
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# Loaders
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In this document, you’ll learn what loaders are in Medusa.
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## Overview
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A loader is a script that runs when the Medusa backend starts. The Medusa backend uses loaders to initialize the database connection, load plugins, register resources in the dependency container, and more.
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Loaders can be created within the Medusa backend codebase, in a plugin, or in a module to perform custom actions when the backend starts. The loader is created in a TypeScript or JavaScript file located in the `src/loaders` directory, then transpiled using the `build` command into the `dist/loaders` directory.
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### Loader Examples
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For example, the Redis Event Bus module uses a loader to establish a connection with Redis and log a message in the console.
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Another example is the Algolia plugin, which uses a loader to update the index settings when the Medusa backend starts based on the plugin’s options.
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Loaders can be used to access the dependency container and register custom resources in it.
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Loaders can also be used to create [scheduled jobs](../scheduled-jobs/overview.mdx) that run at a specified interval of time. For example:
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```ts
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const publishJob = async (container, options) => {
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const jobSchedulerService =
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container.resolve("jobSchedulerService")
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jobSchedulerService.create(
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"publish-products",
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{},
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"0 0 * * *",
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async () => {
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// job to execute
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const productService = container.resolve("productService")
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const draftProducts = await productService.list({
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status: "draft",
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})
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for (const product of draftProducts) {
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await productService.update(product.id, {
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status: "published",
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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 default publishJob
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```
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---
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## Custom Development
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Developers can create a loader with the desired functionality directly within the Medusa Core, in a plugin, or in a module.
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<DocCard item={{
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type: 'link',
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href: '/development/loaders/create',
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label: 'Create a Loader',
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customProps: {
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icon: Icons['academic-cap-solid'],
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description: 'Learn how to create a loader.'
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}
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}} /> |