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Version: 4.x

Validation & Sanitization

Currently inputs received by the server are not checked. Everyone could send anything when requesting POST /api/todos. That's why client inputs cannot be trusted.

You will use the ValidateBody and ValidatePathParam hooks to validate and sanitize incoming data.

A hook is a decorator that is attached to a route handler (a controller method). It is executed before the method and is therefore particularly suitable for validation or access control.

The ValidateBody and ValidatePathParam check respectively the body and params properties of the request object. They take a schema as unique argument.

FoalTS uses Ajv, a fast JSON Schema validator, to define its schemas.

Let's add validation and sanitization to your application. In fact, you have already defined the todo schema in the create-todo script earlier.

import {
ValidateBody, ValidatePathParam
} from '@foal/core';

export class ApiController {


// Every additional properties that are not defined in the "properties"
// object should be removed.
additionalProperties: false,
properties: {
// The "text" property of ctx.request.body should be a string if it exists.
text: { type: 'string' }
// The property "text" is required.
required: [ 'text' ],
// The body request should be an object once parsed by the framework.
type: 'object',
async postTodo(ctx: Context) {
const todo = new Todo();
todo.text = ctx.request.body.text;


return new HttpResponseCreated(todo);

// The id should be a number. If it is not, the hook returns a "400 - Bad Request" error.
@ValidatePathParam('id', { type: 'number' })
async deleteTodo(ctx: Context) {
const todo = await Todo.findOneBy({ id: });
if (!todo) {
return new HttpResponseNotFound();
await todo.remove();
return new HttpResponseNoContent();