You can use the Composer-generated autoloader to load all needed classes:

<?php
require 'vendor/autoload.php';

After you've included the autoloader you should be able to open a Midgard2 repository session:

<?php
// Set up Midgard2 connection
$parameters = array(
    // Use local SQLite file for storage
    'midgard2.configuration.db.type' => 'SQLite',
    'midgard2.configuration.db.name' => 'midgard2cr',
    'midgard2.configuration.db.dir' => __DIR__,
    // Where you want to store file attachments
    'midgard2.configuration.blobdir' => '/var/lib/midgard2/blobs',
    // Let Midgard2 initialize the DB as needed
    'midgard2.configuration.db.init' => true,
);

// Get a Midgard repository
$repository = Midgard\PHPCR\RepositoryFactory::getRepository($parameters);

// Log in to get a session
$credentials = new \PHPCR\SimpleCredentials('admin', 'password');
$session = $repository->login($credentials, 'default');

After this the whole PHPCR API will be available. See some example code in the examples directory.

With MySQL, the connection parameters could for example be:

$parameters = array(
    // MySQL connection settings. The database has to exist
    'midgard2.connection.db.type' => 'MySQL',
    'midgard2.connection.db.name' => 'midgard2',
    'midgard2.connection.db.username' => 'midgard',
    'midgard2.connection.db.password' => 'midgard',
    'midgard2.connection.db.host' => '127.0.0.1',
    'midgard2.connection.db.port' => '3306'
    // Let Midgard2 initialize the DB as needed
    'midgard2.configuration.db.init' => true,
);

This is the only different part from the example using SQLite above.

Midgard2 uses standard relational databases for content storage. The PHPCR model is mapped to database tables in the following way:

• Tree structure is defined in midgard_node table, which contains name, parent reference, and a reference to a content object
• Properties of a node type are stored in the table defined for that node type in its MgdSchema (see examples)
• Multivalued properties, and properties not defined in the node type (for example with nt:unstructured) are stored in the midgard_node_property table, which contains name, reference to midgard_node entry, type and value
• Binary property contents are stored as files into the blobdir defined in repository configuration

New Node Types can be registered by writing MgdSchemas for them and copying them to Midgard's schema directory (by default /usr/share/midgard2/schema).

The Midgard2 PHPCR provider can be used with the Doctrine PHPCR ODM. To start using it, prepare a Midgard2 PHPCR session as explained in the Getting started document, and then:

<?php
// Configuring a Midgard2 PHPCR session before this

// prepare the doctrine configuration
$config = new \Doctrine\ODM\PHPCR\Configuration();

// Create a Document Manager instance for the PHPCR session
$dm = \Doctrine\ODM\PHPCR\DocumentManager::create($session, $config);

// After this you can use PHPCR ODM normally, for example:

// fetching a document by PHPCR path (id in PHPCR ODM lingo)
$user = $dm->getRepository('Namespace\For\Document\User')->find('/bob');
//or let the odm find the document class for you
$user = $dm->find('/bob');

// create a new document
$newUser = new \Namespace\For\Document\User();
$newUser->username = 'Timmy';
$newUser->email = 'foo@example.com';
$newUser->path = '/timmy';
// make the document manager know this document
// this will create the node in PHPCR but not read the 
// fields or commit the changes yet.
$dm->persist($newUser);

// store all changes, insertions, etc. with the storage backend
$dm->flush();

If you're using the Doctrine PHPCR Symfony Bundle, you can also configure PHPCR ODM through it.