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Controllers

Controllers are JavaScript files that contain a set of methods, called actions, reached by the client according to the requested route. Whenever a client requests the route, the action performs the business logic code and sends back the response. Controllers represent the C in the model-view-controller (MVC) pattern.

In most cases, the controllers will contain the bulk of a project's business logic. But as a controller's logic becomes more and more complicated, it's a good practice to use services to organize the code into re-usable parts.

Simplified Strapi backend diagram with controllers highlighted
The diagram represents a simplified version of how a request travels through the Strapi back end, with controllers highlighted. The backend customization introduction page includes a complete, interactive diagram.

Implementation

Controllers can be generated or added manually. Strapi provides a createCoreController factory function that automatically generates core controllers and allows building custom ones or extend or replace the generated controllers.

Adding a new controller

A new controller can be implemented:

  • with the interactive CLI command strapi generate
  • or manually by creating a JavaScript file:
    • in ./src/api/[api-name]/controllers/ for API controllers (this location matters as controllers are auto-loaded by Strapi from there)
    • or in a folder like ./src/plugins/[plugin-name]/server/controllers/ for plugin controllers, though they can be created elsewhere as long as the plugin interface is properly exported in the strapi-server.js file (see Server API for Plugins documentation)
./src/api/restaurant/controllers/restaurant.js
const { createCoreController } = require("@strapi/strapi").factories;

module.exports = createCoreController(
"api::restaurant.restaurant",
({ strapi }) => ({
/**
* Example 1: Modifying a Strapi controller function
*
* If you need to modify the input or output of a pre-defined Strapi controller method,
* write a method of the same name, and use `super` to call the parent method.
* */
async find(ctx) {
// your custom logic for modifying the input
ctx.query = { ...ctx.query, locale: "en" }; // force ctx.query.locale to 'en' regardless of what was requested

// Call the default parent controller action
const result = await super.find(ctx);

// your custom logic for modifying the output
result.meta.date = Date.now(); // change the date that is returned

return result;
},

/**
* Example 2: Replacing a Strapi controller function
*
* If you need to completely replace the behavior of a pre-defined Strapi controller method,
* you can do so by simply implementing a method of the same name.
*
* Caution: You will need to manage the security of the request and results on your own,
* as demonstrated in this example.
* */
async find(ctx) {
// validateQuery throws an error if any of the query params used are inaccessible to ctx.user
// That is, trying to access private fields, fields they don't have permission for, wrong data type, etc
await this.validateQuery(ctx);

// sanitizeQuery silently removes any query params that are invalid or the user does not have access to
// It is recommended to use sanitizeQuery even if validateQuery is used, as validateQuery allows
// a number of non-security-related cases such as empty objects in string fields to pass, while sanitizeQuery
// will remove them completely
const sanitizedQueryParams = await this.sanitizeQuery(ctx);

// Perform whatever custom actions are needed
const { results, pagination } = await strapi
.service("api::restaurant.restaurant")
.find(sanitizedQueryParams);

// sanitizeOutput removes any data that was returned by our query that the ctx.user should not have access to
const sanitizedResults = await this.sanitizeOutput(results, ctx);

// transformResponse correctly formats the data and meta fields of your results to return to the API
return this.transformResponse(sanitizedResults, { pagination });
},

/**
* Example 3: Writing your own new controller function
* If you need to create some new action that does not match one of the pre-configured Strapi methods,
* you can simply add the method with the desired name and implement whatever functionality you want.
*
* Caution: Similar to replacing a controller, you will need to manage the security of the request
* yourself, so remember to use sanitizers and validators as needed.
* */
async healthCheck(ctx) {
ctx.body = "ok";
},
})
);

Each controller action can be an async or sync function. Every action receives a context object (ctx) as a parameter. ctx contains the request context and the response context.

Example: GET /hello route calling a basic controller

A specific GET /hello route is defined, the name of the router file (i.e. index) is used to call the controller handler (i.e. index). Every time a GET /hello request is sent to the server, Strapi calls the index action in the hello.js controller, which returns Hello World!:

./src/api/hello/routes/hello.js
module.exports = {
routes: [
{
method: "GET",
path: "/hello",
handler: "hello.index",
},
],
};
./src/api/hello/controllers/hello.js
module.exports = {
async index(ctx, next) {
// called by GET /hello
ctx.body = "Hello World!"; // we could also send a JSON
},
};
✏️ Note

When a new content-type is created, Strapi builds a generic controller with placeholder code, ready to be customized.

💡 Tip

To see a possible advanced usage for custom controllers, read the services and controllers page of the backend customization examples cookbook.

Sanitization and Validation in controllers

⚠️ Warning

It's strongly recommended you sanitize (v4.8.0+) and/or validate (v4.13.0+) your incoming request query utilizing the new sanitizeQuery and validateQuery functions to prevent the leaking of private data.

Sanitization when utilizing controller factories

Within the Strapi factories the following functions are exposed that can be used for sanitization and validation:

Function NameParametersDescription
sanitizeQueryctxSanitizes the request query
sanitizeOutputentity/entities, ctxSanitizes the output data where entity/entities should be an object or array of data
sanitizeInputdata, ctxSanitizes the input data
validateQueryctxValidates the request query (throws an error on invalid params)
validateInputdata, ctx(EXPERIMENTAL) Validates the input data (throws an error on invalid data)

These functions automatically inherit the sanitization settings from the model and sanitize the data accordingly based on the content-type schema and any of the content API authentication strategies, such as the Users & Permissions plugin or API tokens.

⚠️ Warning

Because these methods use the model associated with the current controller, if you query data that is from another model (i.e., doing a find for "menus" within a "restaurant" controller method), you must instead use the @strapi/utils tools, such as sanitize.contentAPI.query described in Sanitizing Custom Controllers, or else the result of your query will be sanitized against the wrong model.

./src/api/restaurant/controllers/restaurant.js
const { createCoreController } = require("@strapi/strapi").factories;

module.exports = createCoreController(
"api::restaurant.restaurant",
({ strapi }) => ({
async find(ctx) {
await this.validateQuery(ctx);
const sanitizedQueryParams = await this.sanitizeQuery(ctx);
const { results, pagination } = await strapi
.service("api::restaurant.restaurant")
.find(sanitizedQueryParams);
const sanitizedResults = await this.sanitizeOutput(results, ctx);

return this.transformResponse(sanitizedResults, { pagination });
},
})
);

Sanitization and validation when building custom controllers

Within custom controllers, there are 5 primary functions exposed via the @strapi/utils package that can be used for sanitization and validation:

Function NameParametersDescription
sanitize.contentAPI.inputdata, schema, authSanitizes the request input including non-writable fields, removing restricted relations, and other nested "visitors" added by plugins
sanitize.contentAPI.outputdata, schema, authSanitizes the response output including restricted relations, private fields, passwords, and other nested "visitors" added by plugins
sanitize.contentAPI.queryctx.query, schema, authSanitizes the request query including filters, sort, fields, and populate
validate.contentAPI.queryctx.query, schema, authValidates the request query including filters, sort, fields (currently not populate)
validate.contentAPI.inputdata, schema, auth(EXPERIMENTAL) Validates the request input including non-writable fields, removing restricted relations, and other nested "visitors" added by plugins
✏️ Note

Depending on the complexity of your custom controllers, you may need additional sanitization that Strapi cannot currently account for, especially when combining the data from multiple sources.

./src/api/restaurant/controllers/restaurant.js
const { sanitize, validate } = require("@strapi/utils");

module.exports = {
async findCustom(ctx) {
const contentType = strapi.contentType("api::test.test");
await validate.contentAPI.query(ctx.query, contentType, {
auth: ctx.state.auth,
});
const sanitizedQueryParams = await sanitize.contentAPI.query(
ctx.query,
contentType,
{ auth: ctx.state.auth }
);

const entities = await strapi.entityService.findMany(
contentType.uid,
sanitizedQueryParams
);

return await sanitize.contentAPI.output(entities, contentType, {
auth: ctx.state.auth,
});
},
};

Extending core controllers

Default controllers and actions are created for each content-type. These default controllers are used to return responses to API requests (e.g. when GET /api/articles/3 is accessed, the findOne action of the default controller for the "Article" content-type is called). Default controllers can be customized to implement your own logic. The following code examples should help you get started.

💡 Tip

An action from a core controller can be replaced entirely by creating a custom action and naming the action the same as the original action (e.g. find, findOne, create, update, or delete).

💡 Tip

When extending a core controller, you do not need to re-implement any sanitization as it will already be handled by the core controller you are extending. Where possible it's strongly recommended to extend the core controller instead of creating a custom controller.

Collection type examples
💡 Tip

The backend customization examples cookbook shows how you can overwrite a default controller action, for instance for the create action.

async find(ctx) {
// some logic here
const { data, meta } = await super.find(ctx);
// some more logic

return { data, meta };
}
Single type examples
async find(ctx) {
// some logic here
const response = await super.find(ctx);
// some more logic

return response;
}

Usage

Controllers are declared and attached to a route. Controllers are automatically called when the route is called, so controllers usually do not need to be called explicitly. However, services can call controllers, and in this case the following syntax should be used:

// access an API controller
strapi.controller("api::api-name.controller-name");
// access a plugin controller
strapi.controller("plugin::plugin-name.controller-name");
💡 Tip

To list all the available controllers, run yarn strapi controllers:list.