Blog.php

<?php

class Blog
{
    private $dataAccess;

    public function __construct(PostDataAccess $dataAccess)
    {
        $this->dataAccess = $dataAccess;
    }

    public function createPost($title, $body)
    {
        $post = new Post($title, $body);
        $this->dataAccess->save($post);

        return $post;
    }
}

PdoPostDataAccess.php

<?php


class PdoPostDataAccess implements PostDataAccess
{
    private $pdo;

    public function __construct(PDO $pdo)
    {
        $this->pdo = $pdo;
    }

    public function save(Post $post)
    {
        $statement = $this->pdo->prepare('INSERT INTO posts (title, body) VALUES (:title, :body)');

        $statement->bindParam('title', $post->getTitle(), PDO::PARAM_STR);
        $statement->bindParam('body', $post->getBody(), PDO::PARAM_STR);
        $statement->execute();

        $post->setId($this->pdo->lastInsertId());
    }
}

Post.php

<?php

class Post
{
    private $id;

    private $title;

    private $body;

    public function __construct($title, $body)
    {
        $this->title = $title;
        $this->body = $body;
    }

    public function setId($value)
    {
        $this->id = $value;
    }

    public function getId()
    {
        return $this->id;
    }

    public function getTitle()
    {
        return $this->title;
    }

    public function getBody()
    {
        return $this->body;
    }
}

PostDataAccess.php

<?php

interface PostDataAccess
{
    public function save(Post $post);
}

test.php

<?php

require __DIR__ . '/Blog.php';
require __DIR__ . '/Post.php';
require __DIR__ . '/PostDataAccess.php';
require __DIR__ . '/PdoPostDataAccess.php';

$blog = new Blog(new PdoPostDataAccess(new PDO('mysql:host=localhost;dbname=blog;charset=utf8', 'root', 'root')));
$post = $blog->createPost('New post', 'New post text body');

var_dump($post);

/**
 *  Output:
 *
 *  class Post#4 (3)
 *  {
 *      private $id    => string(1) "1"
 *      private $title => string(8) "New post"
 *      private $body  => string(18) "New post text body"
 *  }
 */