php-notes/API.md

Create an API

Route URLs to php files

Routing can be accomplished with a .htaccess file placed in your root directory for the app. This is not PHP related. It's actually something that is a part of Apache. It allows the user to take requests and change them in some way, so that the server thinks the original request came in with modifications specified. For instance you could take all requests to /people/1 and rewrite it to /people?id=1. We'll use this file to specify how our routes map to particular files.

First, tell Apache to allow the ability to rewrite URLs. In .htaccess, add the following:

RewriteEngine On

Now create a route that will map any GET request to /people to people.php

RewriteCond %{REQUEST_METHOD} ^GET$
RewriteRule ^people$ controllers/people.php?action=index

Let's break down the various parts of the first line of the last chunk (RewriteCond %{REQUEST_METHOD} ^GET$):

• RewriteCond
  • this specifies that a rewrite will happen given the following condition
• %{REQUEST_METHOD}
  • this tells apache to look at the request method (GET, POST, PUT/PATCH, DELETE) and compare it to something
• ^GET$
  • this is what the request method will be compared to. In this case, it's the regular expression ^GET$. The ^ denotes the beginning of the string and the $ denotes the end of it.
  • basically, it checks to see if the request method is GET

Now let's break down the second line (RewriteRule ^people$ controllers/people.php?action=index):

• RewriteRule
  • this tells Apache that a rewrite rule follows
• ^people$
  • again this is a regular expression where ^ denotes the beginning of the string and $ denotes the end of the string
  • this says to map any request with a URL that matches people to the file that comes next
• controllers/people.php
  • this is the "controller" file that we'll create shortly. It will handle all routes concerning people
• ?action=index
  • this says to pass a query parameter to that file called action with the value index. You'll see later that we'll use this to query parameter to determine which action (index, show, create, update, delete, etc...) to render

Create a controller file

Create a controllers directory to hold our controller files. Within that directory, create a people.php file. This will handle all routes that pertain to people models.

In this file put the following PHP code (NOTE: I've ommitted <?php and ?> for ease of reading. Don't forget to add each to every file you create from here on out):

if($_REQUEST['action'] === 'index'){
    echo "index route";
}

Go to http://localhost:8888/people to see this in action. Apache will look at our .htaccess file and rewrite the request internally, acting as if the original request was http://localhost:8888/controllers/people.php?action=index

The PHP code we wrote looks at the action query parameter that our .htaccess file tells Apache to create. If its value equals "index", we're going to render the text "index route" to the browser. It does this with the $_REQUEST variable, which we'll look at next.

Every time we use a PHP file to render something server-side, that file has access to several global variables that contain information about the request that was made. $_REQUEST is an associative array that has info about the query parameters that were used in the request. To retrieve the action query parameter that we told Apache to create in our .htaccess file, we can just look at $_REQUEST['action'].

Later on, when we have more routes, we'll have the .htaccess file set the action query parameter to different values depending on what the route is (e.g. show, delete, update, etc). Then in the controller files, we'll test what that value is and use that to determine what JSON to render. Right now we only have index set up in our .htaccess file, so our if statement is unnecessary, but later on in will become important.

Create a model file

Now we're going to a create a file which will end up querying the relational database and turning that information into PHP objects. We call that an Object Relational Mapper (ORM). First, create a models directory, and inside of that create person.php. Add the following code to that file, which will define the Person class used to create people objects:

class Person {
    public $id;
    public $name;
    public $age;
}

This defines the Person class as having three possible properties (id, name, age) which can be edited after the object has been created.

Now, we're going to create a "factory" which will be responsible for generating objects from the database. At the moment, we're just going to have to create some dummy data. Add the following to the bottom of models/person.php:

class People {
    static function find(){
        //create an empty array
        $people = array();

        //create some random people
        $person1 = new Person(1,'Bob', 32);
        $person2 = new Person(1,'Bob', 32);
        $person3 = new Person(1,'Bob', 32);

        //push the people onto the array
        $people[] = $person1;
        $people[] = $person2;
        $people[] = $person3;

        //return the array of people
        return $people;
    }
}

Use the people model in the controller

Now that we have our People/Person model set up, we need to incorporate it into our People controller. First include it into our controllers/people.php:

include_once __DIR__ . '/../models/person.php';

• include_once will include the file, unless it's already been included somewhere else in our app. We could use include, but include_once keeps us from accidentally running the models/people.php more than once.
• __DIR__ just spits out the full absolute path the directory of the current file that's running that line of code
• /../models/person.php: since we're currently in the controllers directory, we need to travel up a level to the project's root dir and then into the models/ directory. We then reference the person.php file in that directory

Now that we wrote that code, we have our Person and People classes available to us. Let's replace

echo "index route";

with

echo json_encode(People::find());

This will render the results of People::find() (an array of Person objects) as JSON. Refresh http://localhost:8888/people to see the difference.

Add a Content-Type header

Most JavaScript libraries/frameworks that deal with AJAX (e.g. Angular, Axios, fetch, etc) expect a special header to be set in all AJAX responses, telling the requesting client what kind of data is being sent back. Let's add this to the top of controllers/people.php:

header('Content-Type: application/json');

This is meta data meant just for the client application (the browser). It isn't part of the response body, so the end user won't see it. If you look at http://localhost:8888/people, you won't see anything about Content-Type: application/json, but it will be available to your AJAX libraries/frameworks.

NOTE, this code has to come at the top of the file, before any content is written to response body.

Prepare Postgres for the app

In order to have PHP interact with Postgres, there are a few things we need to do before hand

First, start postgres. In the terminal, type:

postgres -D /usr/local/var/postgres/

Next, open up a new terminal tab/window and type:

psql postgres

Now we want to create a sub-database for our application (we'll name it contacts). In the psql tab, type:

CREATE DATABASE contacts;

and now connect to it:

\c contacts

Now we want to create a table for our people:

CREATE TABLE people (id SERIAL, name VARCHAR(16), age INT);

Let's insert some people:

INSERT INTO users ( name, age ) VALUES ( 'Matt', 38 );
INSERT INTO users ( name, age ) VALUES ( 'Sally', 54 );
INSERT INTO users ( name, age ) VALUES ( 'Zanthar', 4892 );

Connect the People model to Postgres

Currently, our People model's find function randomly generates three Person objects when invoked. Let's have it connect to postgres so that it can use the rows we inserted into the people table to create the Person objects. At the top of models/person.php add the following:

$dbconn = pg_connect("host=localhost dbname=contacts");

Now that we're connected to Postgres, we can have PHP query the database. In models/person.php, let's alter our find function:

class People {
    static function find(){
        //create an empty array
        $people = array();

        //query the database
        $results = pg_query("SELECT * FROM people");

        return $people;
    }
}

Our $results variable is a result set. It's basically like a PHP version of the rows retrieved from Postgres. Now we'll use the pg_fetch_object function to remove the first row from the $results dataset and turn it into an object:

$results = pg_query("SELECT * FROM people");
$row_object = pg_fetch_object($results); //remove a row from the results and turn it into an object

To see what our $row_object looks like, let's add the following:

$results = pg_query("SELECT * FROM people");
$row_object = pg_fetch_object($results);
var_dump($row_object); //print values of the object
die(); //halt execution

Now we can see the various values that are available to us for the row that was returned.

• var_dump will take any object and print its values
• die will halt execution from continuing so that you can read what was printed

If we keep removing rows from $results, we'll eventually run out of rows. When this happens, pg_fetch_object returns false

$results = pg_query("SELECT * FROM people");

$row_object = pg_fetch_object($results);
var_dump($row_object);

$row_object = pg_fetch_object($results);
var_dump($row_object);

$row_object = pg_fetch_object($results);
var_dump($row_object);

$row_object = pg_fetch_object($results);
var_dump($row_object);

die();

Let's change this so it does this with a while loop. This way, no matter how many rows are in the results, all will be printed:

class People {
    static function find(){
        //create an empty array
        $people = array();

        //query the database
        $results = pg_query("SELECT * FROM people");

        $row_object = pg_fetch_object($results)
        while($row_object){
            var_dump($row_object);
            $row_object = pg_fetch_object($results);
        }
        die();

        return $people;
    }
}

Now, as long as $results has rows, while($row_object) will run its code. As soon as all the rows have been removed, $row_object will be false and the while loop will exit.

Now that we can see the various rows in our $results as objects, we can use this info to create Person objects which we'll push onto our $people array.

class People {
    static function find(){
        //create an empty array
        $people = array();

        //query the database
        $results = pg_query("SELECT * FROM people");

        $row_object = pg_fetch_object($results)
        while($row_object){

            $new_person = new Person( //create a new person
                $row_object->id,
                $row_object->name,
                $row_object->age,
            );
            $people[] = $new_person; //push new person object onto $people array

            $row_object = pg_fetch_object($results);
        }

        return $people;
    }
}

One thing you might notice is that the id and age values for each person are strings. Let's change those into integers:

$new_person = new Person(
    intval($row_object->id),
    $row_object->name,
    intval($row_object->age),
);