Creating a RESTful API: POST requests

To demonstrate the handling of POST requests, we will create a handler that add a new element to the array of courses.

router.post("/", (req, res) => {
  const course = {
    id: courses.length + 1,
    name: req.body.name,
  };
  courses.push(course);
  res.send(course);
});

Here we use the body that is sent from the client and isolate the field name. This presupposes that the client is sending us data with the following shape as the body:

{
  "name": "Biology and Life Sciences"
}

To execute the PUT request from the frontend:

const addCourse = async (newCourse) => {
  try {
    const resp = await axios.post("http://localhost:3000/api/courses", {
      name: newCourse,
    });
    console.log(resp.data);
  } catch (err) {
    console.error(err);
  }
};
addCourse("Biology and Life Sciences");

Which returns:

{ id: 4, name: 'Biology and Life Sciences' }

The id is added by the server, not the client. Having created the new value we add it to our courses array. (In reality we would be creating a new entry in a database.) Then we follow the convention of returning the new value back to the client.

Validation

We should accept alterations to the database that are not first validated. We can use the Joi validator to vet the request:

function validateCourse(course) {
  const schema = Joi.object({
    name: Joi.string().min(3).required(),
  });

  const { error } = schema.validate(course);
  return error;
}

We can then add the validation as part of our general error handling:

router.post("/", (req, res) => {
  const course = {
    id: courses.length + 1,
    name: req.body.name,
  };
  const { error } = schema.validate(req.body);
  if (error)
    return error.details.map((joiErr) => res.status(400).send(joiErr.message));

  courses.push(course);
  res.send(course);
});
logo