04 - Crafting the Response

In this module, we'll use the then() function to return a Promise for our request.

Overview

It's great that our model and routes are working, but there was a slight hiccup with our last post: If you look at the console, you'll see that the success message actually printed BEFORE the data was inserted into the database. What if the insert had failed though and the data couldn't be entered? For this reason, we need to make sure that the response to the user comes AFTER the insert statement.

The Code

Go into the testcontroller.js file and add the following method. Add it to the bottom of the file, but above the export statement.

//STEP 4 - Use this with Postman
router.post('/four', function (req, res) {
  var testData = req.body.testdata.item;
  TestModel
    .create({
      testdata: testData
    })
    .then( //1
      function message() { //2
       res.send("Test 4 went through!");
      }
    );
});

Analysis

Here are the updates that we've made: 1. We call the then() method. As you'll read in the the MDN docs, the then() method returns a Promise. Hence, we use this asynchronous function to force the message to wait for the insert statement to finish. 2. The callback function will print the success message to the console once testData is done running.

Testing

Let's use Postman to test this:

1. Make sure your server is running.

2. Open Postman.

3. Open a new request.

4. Change the dropdown to POST.

5. Enter the endpoint into the URL: http://localhost:3000/test/four.

6. Click on the body tab under the url input field.

7. Choose the raw radio button.

8. In the dropdown, choose JSON (application/json).

9. In the empty space, add a JSON object like the one below:

{
    "testdata":{
        "item":"step 4"
    }
}

10. Press send.

11. You should see the following:

screenshot

12. Let's also go to Postgres and make sure the data is there. To update the table, you can press the Execute button (the lightning bolt).

screenshot

Summary of the Flow

In this module, the following flow is happening:

1. We make a POST request with Postman.

2. body-parser breaks the request into JSON.

3. The router sends the request to the testcontroller.

4. The controller with the /four endpoint is called.

5. The req.body.testdata.item is captured in the testData variable.

6. We then use the Sequelize create() method to create the object to be sent to the DB.

7. The object is sent to Postgres, which stores it.

8. After the data is stored, we fire the then() method, which returns a Promise.

9. A method fires a response to Postman.