SQL Abstraction and Object Hydration

In the last chapter, we introduced database abstraction and a new command interface for operations that might change what blog posts we store. We'll now start creating database-backed versions of the PostRepositoryInterface and PostCommandInterface, demonstrating usage of the various Zend\Db\Sql classes.

Preparing the Database

This tutorial assumes you've followed the Getting Started tutorial, and that you've already populated the data/zftutorial.db SQLite database. We will be re-using it, and adding another table to it.

Create the file data/posts.schema.sql with the following contents:

CREATE TABLE posts (id INTEGER PRIMARY KEY AUTOINCREMENT, title varchar(100) NOT NULL, text TEXT NOT NULL);

INSERT INTO posts (title, text) VALUES ('Blog #1', 'Welcome to my first blog post');
INSERT INTO posts (title, text) VALUES ('Blog #2', 'Welcome to my second blog post');
INSERT INTO posts (title, text) VALUES ('Blog #3', 'Welcome to my third blog post');
INSERT INTO posts (title, text) VALUES ('Blog #4', 'Welcome to my fourth blog post');
INSERT INTO posts (title, text) VALUES ('Blog #5', 'Welcome to my fifth blog post');

Now we will execute this against the existing data/zftutorial.db SQLite database using the sqlite command (or sqlite3; check your operating system):

$ sqlite data/zftutorial.db < data/posts.schema.sql

If you don't have a sqlite command, you can populate it using PHP. Create the following script in data/load_posts.php:

<?php
$db = new PDO('sqlite:' . realpath(__DIR__) . 'zftutorial.db');
$fh = fopen(__DIR__ . '/posts.schema.sql', 'r');
while ($line = fread($fh, 4096)) {
    $line = trim($line);
    $db->exec($line);
}
fclose($fh);

and execute it using:

$ php data/load_posts.php

Quick Facts Zend\Db\Sql

To create queries against a database using Zend\Db\Sql, you need to have a database adapter available. The "Getting Started" tutorial covered this in the database chapter, and we can re-use that adapter.

With the adapter in place and the new table populated, we can run queries against the database. The construction of queries is best done through the "QueryBuilder" features of Zend\Db\Sql which are Zend\Db\Sql\Sql for select queries, Zend\Db\Sql\Insert for insert queries, Zend\Db\Sql\Update for update queries and Zend\Db\Sql\Delete for delete queries. The basic workflow of these components is:

  1. Build a query using the relevant class: Sql, Insert, Update, or Delete.
  2. Create a SQL statement from the Sql object.
  3. Execute the query.
  4. Do something with the result.

Let's start writing database-driven implementations of our interfaces now.

Writing the repository implementation

Create a class named ZendDbSqlRepository in the Blog\Model namespace that implements PostRepositoryInterface; leave the methods empty for now:

// In module/Blog/src/Model/ZendDbSqlRepository.php:
namespace Blog\Model;

use InvalidArgumentException;
use RuntimeException;

class ZendDbSqlRepository implements PostRepositoryInterface
{
    /**
     * {@inheritDoc}
     */
    public function findAllPosts()
    {
    }

    /**
     * {@inheritDoc}
     * @throws InvalidArgumentException
     * @throws RuntimeException
     */
    public function findPost($id)
    {
    }
}

Now recall what we have learned earlier: for Zend\Db\Sql to function, we will need a working implementation of the AdapterInterface. This is a requirement, and therefore will be injected using constructor injection. Create a __construct() method that accepts an AdapterInterface as its sole parameter, and stores it as an instance property:

// In module/Blog/src/Model/ZendDbSqlRepository.php:
namespace Blog\Model;

use InvalidArgumentException;
use RuntimeException;
use Zend\Db\Adapter\AdapterInterface;

class ZendDbSqlRepository implements PostRepositoryInterface
{
    /**
     * @var AdapterInterface
     */
    private $db;

    /**
     * @param AdapterInterface $db
     */
    public function __construct(AdapterInterface $db)
    {
        $this->db = $db;
    }

    /**
     * {@inheritDoc}
     */
    public function findAllPosts()
    {
    }

    /**
     * {@inheritDoc}
     * @throws InvalidArgumentException
     * @throws RuntimeException
     */
    public function findPost($id)
    {
    }
}

Whenever we have a required parameter, we need to write a factory for the class. Go ahead and create a factory for our new repository implementation:

// In module/Blog/src/Factory/ZendDbSqlRepositoryFactory.php
namespace Blog\Factory;

use Interop\Container\ContainerInterface;
use Blog\Model\ZendDbSqlRepository;
use Zend\Db\Adapter\AdapterInterface;
use Zend\ServiceManager\Factory\FactoryInterface;

class ZendDbSqlRepositoryFactory implements FactoryInterface
{
    /**
     * @param ContainerInterface $container
     * @param string $requestedName
     * @param null|array $options
     * @return ZendDbSqlRepository
     */
    public function __invoke(ContainerInterface $container, $requestedName, array $options = null)
    {
        return new ZendDbSqlRepository($container->get(AdapterInterface::class));
    }
}

We're now able to register our repository implementation as a service. To do so, we'll make two changes:

Update module/Blog/config/module.config.php as follows:

return [
    'service_manager' => [
        'aliases' => [
            // Update this line:
            Model\PostRepositoryInterface::class => Model\ZendDbSqlRepository::class,
        ],
        'factories' => [
            Model\PostRepository::class => InvokableFactory::class,
            // Add this line:
            Model\ZendDbSqlRepository::class => Factory\ZendDbSqlRepositoryFactory::class,
        ],
    ],
    'controllers'  => [ /* ... */ ],
    'router'       => [ /* ... */ ],
    'view_manager' => [ /* ... */ ],
];

With the adapter in place you're now able to refresh the blog index at localhost:8080/blog and you'll notice that the ServiceNotFoundException is gone and we get the following PHP Warning:

Warning: Invalid argument supplied for foreach() in {projectPath}/module/Blog/view/blog/list/index.phtml on line {lineNumber}

This is due to the fact that our mapper doesn't return anything yet. Let's modify the findAllPosts() function to return all blog posts from the database table:

// In /module/Blog/src/Model/ZendDbSqlRepository.php:
namespace Blog\Model;

use InvalidArgumentException;
use RuntimeException
use Zend\Db\Adapter\AdapterInterface;
use Zend\Db\Sql\Sql;

class ZendDbSqlRepository implements PostRepositoryInterface
{
    /**
     * @var AdapterInterface
     */
    private $db;

    /**
     * @param AdapterInterface $db
     */
    public function __construct(AdapterInterface $db)
    {
        $this->db = $db;
    }

    /**
     * {@inheritDoc}
     */
    public function findAllPosts()
    {
        $sql    = new Sql($this->db);
        $select = $sql->select('posts');
        $stmt   = $sql->prepareStatementForSqlObject($select);
        $result = $stmt->execute();
        return $result;
    }

    /**
     * {@inheritDoc}
     * @throws InvalidArgumentException
     * @throw RuntimeException
     */
    public function findPost($id)
    {
    }
}

Sadly, though, a refresh of the application reveals another error message:

PHP Fatal error:  Call to a member function getId() on array in {projectPath}/module/Blog/view/blog/list/index.phtml on line {lineNumber}

Let's not return the $result variable for now and do a dump of it to see what we get here. Change the findAllPosts() method and dump the result:

public function findAllPosts()
{
    $sql    = new Sql($this->db);
    $select = $sql->select('posts');
    $stmt   = $sql->prepareStatementForSqlObject($select);
    $result = $stmt->execute();

    var_export($result);
    die();

    return $result;
}

Refreshing the application you should now see output similar to the following:

Zend\Db\Adapter\Driver\Pdo\Result::__set_state(array(
    'statementMode'   => 'forward',
    'fetchMode'       => 2,
    'resource'        => PDOStatement::__set_state(array(
        'queryString' => 'SELECT "posts".* FROM "posts"',
    )),
    'options'         => null,
    'currentComplete' => false,
    'currentData'     => null,
    'position'        => -1,
    'generatedValue'  => '0',
    'rowCount'        => Closure::__set_state(array()),
))

As you can see, we do not get any data returned. Instead we are presented with a dump of some Result object that appears to have no data in it whatsoever. But this is a faulty assumption. This Result object only has information available for you when you actually try to access it. If you can determine that the query was successful, the best way to make use of the data within the Result object is to pass it to a ResultSet object.

First, add two more import statements to the class file:

use Zend\Db\Adapter\Driver\ResultInterface;
use Zend\Db\ResultSet\ResultSet;

Now update the findAllPosts() method as follows:

public function findAllPosts()
{
    $sql    = new Sql($this->db);
    $select = $sql->select('posts');
    $stmt   = $sql->prepareStatementForSqlObject($select);
    $result = $stmt->execute();

    if ($result instanceof ResultInterface && $result->isQueryResult()) {
        $resultSet = new ResultSet();
        $resultSet->initialize($result);
        var_export($resultSet);
        die();
    }

    die('no data');
}

Refreshing the page, you should now see the dump of a ResultSet instance:

Zend\Db\ResultSet\ResultSet::__set_state(array(
    'allowedReturnTypes'   =>
        array(
            0 => 'arrayobject',
            1 => 'array',
        ),
    'arrayObjectPrototype' =>
        ArrayObject::__set_state(array(
        )),
    'returnType'           => 'arrayobject',
    'buffer'               => null,
    'count'                => null,
    'dataSource'           =>
        Zend\Db\Adapter\Driver\Pdo\Result::__set_state(array(
            'statementMode'   => 'forward',
            'fetchMode'       => 2,
            'resource'        =>
                PDOStatement::__set_state(array(
                    'queryString' => 'SELECT "album".* FROM "album"',
                )),
            'options'         => null,
            'currentComplete' => false,
            'currentData'     => null,
            'position'        => -1,
            'generatedValue'  => '0',
            'rowCount'        =>
                Closure::__set_state(array(
                )),
        )),
    'fieldCount'           => 3,
    'position'             => 0,
))

Of particular interest is the returnType property, which has a value of arrayobject. This tells us that all database entries will be returned as an ArrayObject instances. And this is a little problem for us, as the PostRepositoryInterface requires us to return an array of Post instances. Luckily the Zend\Db\ResultSet subcomponent offers a solution for us, via the HydratingResultSet; this result set type will populate an object of a type we specify with the data returned.

Let's modify our code. First, remove the following import statement from the class file:

use Zend\Db\ResultSet\ResultSet;

Next, we'll add the following import statements to our class file:

use Zend\Hydrator\Reflection as ReflectionHydrator;
use Zend\Db\ResultSet\HydratingResultSet;

Now, update the findAllPosts() method to read as follows:

public function findAllPosts()
{
    $sql       = new Sql($this->db);
    $select    = $sql->select('posts');
    $statement = $sql->prepareStatementForSqlObject($select);
    $result    = $statement->execute();

    if (! $result instanceof ResultInterface || ! $result->isQueryResult()) {
        return [];
    }

    $resultSet = new HydratingResultSet(
        new ReflectionHydrator(),
        new Post('', '')
    );
    $resultSet->initialize($result);
    return $resultSet;
}

We have changed a couple of things here. First, instead of a normal ResultSet, we are now using the HydratingResultSet. This specialized result set requires two parameters, the second one being an object to hydrate with data, and the first one being the hydrator that will be used (a hydrator is an object that will transform an array of data into an object, and vice versa). We use Zend\Hydrator\Reflection here, which is capable of injecting private properties of an instance. We provide an empty Post instance, which the hydrator will clone to create new instances with data from individual rows.

Instead of dumping the $result variable, we now directly return the initialized HydratingResultSet so we can access the data stored within. In case we get something else returned that is not an instance of a ResultInterface, we return an empty array.

Refreshing the page you will now see all your blog posts listed on the page. Great!

Refactoring hidden dependencies

There's one little thing that we have done that's not a best-practice. We use both a hydrator and an Post prototype inside our ZendDbSqlRepository. Let's inject those instead, so that we can reuse them between our repository and command implementations, or vary them based on environment. Update your ZendDbSqlRepository as follows:

// In module/Blog/src/Model/ZendDbSqlRepository.php:
namespace Blog\Model;

use InvalidArgumentException;
use RuntimeException;
// Replace the import of the Reflection hydrator with this:
use Zend\Hydrator\HydratorInterface;
use Zend\Db\Adapter\AdapterInterface;
use Zend\Db\Adapter\Driver\ResultInterface;
use Zend\Db\ResultSet\HydratingResultSet;
use Zend\Db\Sql\Sql;

class ZendDbSqlRepository implements PostRepositoryInterface
{
    /**
     * @var AdapterInterface
     */
    private $db;

    /**
     * @var HydratorInterface
     */
    private $hydrator;

    /**
     * @var Post
     */
    private $postPrototype;

    public function __construct(
        AdapterInterface $db,
        HydratorInterface $hydrator,
        Post $postPrototype
    ) {
        $this->db            = $db;
        $this->hydrator      = $hydrator;
        $this->postPrototype = $postPrototype;
    }

    /**
     * Return a set of all blog posts that we can iterate over.
     *
     * Each entry should be a Post instance.
     *
     * @return Post[]
     */
    public function findAllPosts()
    {
        $sql       = new Sql($this->db);
        $select    = $sql->select('posts');
        $statement = $sql->prepareStatementForSqlObject($select);
        $result    = $statement->execute();

        if (! $result instanceof ResultInterface || ! $result->isQueryResult()) {
            return [];
        }

        $resultSet = new HydratingResultSet($this->hydrator, $this->postPrototype);
        $resultSet->initialize($result);
        return $resultSet;
    }

    /**
     * Return a single blog post.
     *
     * @param  int $id Identifier of the post to return.
     * @return Post
     */
    public function findPost($id)
    {
    }
}

Now that our repository requires more parameters, we need to update the ZendDbSqlRepositoryFactory and inject those parameters:

// In /module/Blog/src/Factory/ZendDbSqlRepositoryFactory.php
namespace Blog\Factory;

use Interop\Container\ContainerInterface;
use Blog\Model\Post;
use Blog\Model\ZendDbSqlRepository;
use Zend\Db\Adapter\AdapterInterface;
use Zend\Hydrator\Reflection as ReflectionHydrator;
use Zend\ServiceManager\Factory\FactoryInterface;

class ZendDbSqlRepositoryFactory implements FactoryInterface
{
    public function __invoke(ContainerInterface $container, $requestedName, array $options = null)
    {
        return new ZendDbSqlRepository(
            $container->get(AdapterInterface::class),
            new ReflectionHydrator(),
            new Post('', '')
        );
    }
}

With this in place you can refresh the application again and you'll see your blog posts listed once again. Our repository no longer has hidden dependencies, and works with a database!

Finishing the repository

Before we jump into the next chapter, let's quickly finish the repository implementation by completing the findPost() method:

public function findPost($id)
{
    $sql       = new Sql($this->db);
    $select    = $sql->select('posts');
    $select->where(['id = ?' => $id]);

    $statement = $sql->prepareStatementForSqlObject($select);
    $result    = $statement->execute();

    if (! $result instanceof ResultInterface || ! $result->isQueryResult()) {
        throw new RuntimeException(sprintf(
            'Failed retrieving blog post with identifier "%s"; unknown database error.',
            $id
        ));
    }

    $resultSet = new HydratingResultSet($this->hydrator, $this->postPrototype);
    $resultSet->initialize($result);
    $post = $resultSet->current();

    if (! $post) {
        throw new InvalidArgumentException(sprintf(
            'Blog post with identifier "%s" not found.',
            $id
        ));
    }

    return $post;
}

The findPost() function looks similar to the findAllPosts() method, with several differences.

Conclusion

Finishing this chapter, you now know how to query for data using the Zend\Db\Sql classes. You have also learned a little about the zend-hydrator component, and the integration zend-db provides with it. Furthermore, we've continued demonstrating dependency injection in all aspects of our application.

In the next chapter we'll take a closer look at the router so we'll be able to start displaying individual blog posts.