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.

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)

// path: ./src/api/restaurant/controllers/restaurant.js

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

module.exports = createCoreController('api::restaurant.restaurant', ({ strapi }) =>  ({
  // Method 1: Creating an entirely custom action
  async exampleAction(ctx) {
    try {
      ctx.body = 'ok';
    } catch (err) {
      ctx.body = err;
    }
  },

  // Method 2: Wrapping a core action (leaves core logic in place)
  async find(ctx) {
    // some custom logic here
    ctx.query = { ...ctx.query, local: 'en' }
    
    // Calling the default core action
    const { data, meta } = await super.find(ctx);

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

    return { data, meta };
  },

  // Method 3: Replacing a core action
  async findOne(ctx) {
    const { id } = ctx.params;
    const { query } = ctx;

    const entity = await strapi.service('api::restaurant.restaurant').findOne(id, query);
    const sanitizedEntity = await this.sanitizeOutput(entity, ctx);

    return this.transformResponse(sanitizedEntity);
  }
}));

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!:

// path: ./src/api/hello/routes/hello.js

module.exports = {
  routes: [
    {
      method: 'GET',
      path: '/hello',
      handler: 'hello.index',
    }
  ]
}

// path: ./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.

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).

Collection type examples

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

  return { data, meta };
}

async findOne(ctx) {
  // some logic here
  const response = await super.findOne(ctx);
  // some more logic

  return response;
}

async create(ctx) {
  // some logic here
  const response = await super.create(ctx);
  // some more logic

  return response;
}

async update(ctx) {
  // some logic here
  const response = await super.update(ctx);
  // some more logic

  return response;
}

async delete(ctx) {
  // some logic here
  const response = await super.delete(ctx);
  // some more logic

  return response;
}

Single type examples

async find(ctx) {
  // some logic here
  const response = await super.find(ctx);
  // some more logic

  return response;
}

async update(ctx) {
  // some logic here
  const response = await super.update(ctx);
  // some more logic

  return response;
}

async delete(ctx) {
  // some logic here
  const response = await super.delete(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.