With the example backend running atlocalhost:4000, open the Postman App. You should see an interface that looks like this:

postman_interface

At the top of the window, you can see a dropdown that lets you choose what kind of HTTP operation to perform. By default, it is set to GET. If you expand the dropdown, you will see all of the possible HTTP methods you can use to interact with this system:

requests_dropdown

To see all of the users that are currently in the database, make a GET request tolocalhost:4000/users. To do this, you should:

• Make sure the dropdown is set to GET.
• Enter the URLlocalhost:4000/usersin the textbox that says “Enter request URL”.

When the you have entered this information, press the Send button:

send_get_request

The body of the response will appear in the panel at the bottom of the window. You should see two users stored, each with a uniqueid:

{
    "users": [
        {
            "id": 1,
            "username": "1lameuser",
            "password": "secret_password"
        },
        {
            "id": 2,
            "username": "cool_user_87",
            "password": "notPassword!"
        }
   ]
}

This tells us that there are currently two users stored in the database. One has ausernamewith the value“1lameuser”and apasswordwith the value“secret_password”, and the other has ausernamewith the value“cool_user_87”and apasswordwith the value“notPassword!”.

We can also GET a specific user by specifying anidin the URL of the GET request. To get the user“1lameuser”, for example, we can send this GET request:localhost:4000/users/1. The response to this request should be:

{
    "user": {
        "id": 1,
        "username": "1lameuser",
        "password": "secret_password"
    }
}

These GET requests only retrieved resources from the server. No information was changed. Next, we’ll look at how to use Postman to send requests to add users to the system.

We can use POST requests to add users to the database. Let’s practice with sending some POST requests.

• Change the type of request from GET to POST using Postman’s dropdown selector.
• Add the request URL (localhost:4000/users) in the appropriate textbox.
• In order to create a new resource in this database, we need to supply auserobject to create in the body of the POST request. Select the “Body” tab and check the “raw” radio button to specify input.
• The type of input should be aJSONobject, so select the dropdown that says “Text” and change it to “JSON (application/json)”:
• In the text input field underneath the radio buttons, type in whateveruserobject you want to add. For a valid POST request for this server, you should include JSON in the request body that has this format:{"user": {"username":<String>, "password":<String>}}Here is an example of what the interface will look like before you send the request:
• Press the Send button to send the POST request.Look at the output. What is contained in the response body? Is this what you would expect? For the above example, the output in the response body looks like:{ "user": { "id": 3, "username": "wholeNewUser", "password": "IllNeverTell" } }This response means that a user withusername“wholeNewUser”,password“IllNeverTell”, andid3 was added to theusersresource.

request_type

{"user": {"username":<String>, "password":<String>}}

post_request

{
    "user": {
        "id": 3,
        "username": "wholeNewUser",
        "password": "IllNeverTell"
    }
}

Let’s try sending some more requests.

• Add a user to the system with your first name (as a String) as the username and your last name (as a String) as the password. Use POST to do this, with auserobject in the body as a JSON.
• Look at all of the users contained in theusersresource now. Use a GET request to do this.
• Retrieve the user withid4 only. Use a GET request with a specifiedidto do this.

Great work! You now can use Postman to make requests and see the corresponding responses. This will be very helpful in testing and understanding the APIs you build.

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