v4 code migration: Updating controllers

This guide is part of the v4 code migration guide designed to help you migrate the code of a Strapi application from v3.6.x to v4.0.x

🤓 v3/v4 comparison

In both Strapi v3 and v4, creating content-types automatically generates core API controllers. Controllers are JavaScript files that contain a list of methods, called actions.

In Strapi v3, controllers export an object containing actions that are merged with the existing actions of core API controllers, allowing customization.

In Strapi v4, controllers export the result of a call to the createCoreController factory function, with or without further customization.

Migrating controllers to Strapi v4 consists in making sure that each controller is located in the proper folder and uses the createCoreController factory function introduced in v4.

Due to the differences between controllers implementation in Strapi v3 and v4, it's recommended to create a new controller file, then optionally bring existing v3 customizations into the new file and adapt them when necessary.

✏️ Note

The controller file can be created automatically with the interactive CLI command strapi generate.

To create a v4 controller:

Create a api/<api-name>/controllers/<controller-name>.js file inside the ./src folder (see project structure).
Copy and paste the following code at the top of the ./src/api/<api-name>/controllers/<controller-name>.js file. The code imports the createCoreController factory function from the factories included with the core of Strapi:
```
const { createCoreController } = require('@strapi/strapi').factories;
```
Copy and paste the following code, replacing api-name and content-type-name with appropriate names. The code exports the result of a call to the createCoreController factory function, passing the unique identifier of the content-type (e.g. api::api-name.content-type-name) as an argument:
```
module.exports = createCoreController('api::api-name.content-type-name')
```
(optional) To customize controller actions, pass a second argument to the createCoreController factory function. This argument can be either an object or a function returning an object. The object contains methods, which can either be entirely new actions or replace or extend existing actions of core API controllers (see controllers implementation documentation).

Example of a v4 controller without customization:

./src/api/<content-type-name>/controllers/<controller-name>.js

const { createCoreController } = require('@strapi/strapi').factories;

module.exports = createCoreController('api::api-name.content-type-name');

Example of a v4 controller with customization:

./src/api/<content-type-name>/controllers/<controller-name>.js

const { createCoreController } = require('@strapi/strapi').factories;

module.exports = createCoreController('api::api-name.content-type-name', ({ strapi }) => ({
  // wrap a core action, leaving core logic in place
  async find(ctx) {
    // some custom logic here
    ctx.query = { ...ctx.query, local: 'en' }

    // calling the default core action with super
    const { data, meta } = await super.find(ctx);

    // some more custom logic
    meta.date = Date.now()

    return { data, meta };
  },
}));

💡 Customization tips

The original controller’s CRUD actions can be called using super (e.g. super.find()).
The sanitizeInput and sanitizeOutput utilities can be used in Strapi v4 and replace the sanitizeEntity utility from v3.

More examples can be found in the controllers implementation documentation.

🤓 Next steps

Migrating the backend code of Strapi to v4 also requires to at least migrate the core features of the Strapi server, such as the configuration, dependencies, routes, services, and content-type schemas.