Transparent Object Persistence (within FLOW3)

Transparent Object
Persistence
(within FLOW3)
Karsten Dambekalns <karsten@typo3.org>

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Samstag, 16. Mai 2009

“DDD persistence”
Domain Models encapsulate behavior and data

Concerned about the problem – only

Infrastructure is of no relevance

Unfortunately you need to be aware of the infrastructure at
some point – at least a little

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Entities
Identity is important

Are not deﬁned by their attributes

Examples could be...

• Projects

• Developers

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Value objects
Have no indentity

Their value is of importance

Are interchangeable

Examples could be...

• Colors

• Numbers

• Tags in Forge

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Aggregates
Cluster associated objects

Have a boundary and a root

The root is a speciﬁc entity

References from outside point to the root

An example for an aggregate:

• Project

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Repositories
Provide access to entities (and aggregates)

Allow to ﬁnd a starting point for traversal

Persisted objects can be searched for

Queries can be built in various ways

Handle storage of additions and updates

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A Domain Model
Project
Repository

Project
Developer

SVN twitter
Account Account

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A Domain Model
Project
Repository
it

Project
Repos

Developer

SVN twitter
Account Account

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A Domain Model
Project
Repository
it

Project
Repos

Developer
Aggre-
gates SVN twitter
Account Account

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A Domain Model

Developer

SVN twitter
Account Account

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Using FLOW3...
You just implement the model

No need to care about persisting your model

FLOW3 handles this for you – transparently

Even a Repository only needs little work

Deﬁne relevant metadata in the source ﬁle using annotations

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@nnotations used

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@nnotations used
@entity

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@nnotations used
@entity

@valueobject

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@nnotations used
@entity

@valueobject

@var

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@nnotations used
@entity

@valueobject

@var

@transient

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@nnotations used
@entity

@valueobject

@var

@transient

@uuid

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@nnotations used
@entity

@valueobject

@var

@transient

@uuid

@identity

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@nnotations used
@entity

@valueobject

@var

@transient

@uuid

@identity

@lazy

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Persistence Manager
Mostly invisible to developers

Manages additions of and updates to objects

Concerned only about objects in repositories

Collects objects and hands over to backend

Allows for objects being persisted at any time

Automatically called to persist at end of script run

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Simpliﬁed stack

SQLite PgSQL MySQL ...

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Simpliﬁed stack

PDO ...

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Simpliﬁed stack

TYPO3 Content Repository
PDO ...

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Simpliﬁed stack

FLOW3 Persistence

PDO ...

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Simpliﬁed stack
Application Application

FLOW3 Persistence

PDO ...

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Simpliﬁed stack
FLOW3 Persistence

Persistence
TYPO3 CR
Backend

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TYPO3 CR
FLOW3

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Transparent persistence
Explicit support for Domain-Driven Design

Class Schemata are defined by the Domain Model class

• No need to write an XML or YAML schema definition

• No need to define the database model and object model
multiple times at different places

Automatic persistence in the JSR-283 based Content Repository

Legacy data sources can be mounted

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Query Factory
Creates a query for you

Decouples persistence layer from backend

Must be implemented by backend

API with one method:

• public function create($className);

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Query objects
Represent a query for an object type

Allow criteria to be attached

Must be implemented by backend

Simple API

• execute()

• matching()

• equals(), lessThan(), ...

• ...

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Object reconstitution
When fetching objects the content repository looks for
matching nodes

The nodes are mapped to objects by a data mapper

Reconstitution

• does not call __construct()

• restores all non-transient properties

• reinjects dependencies (skips constructor arguments)

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public function map(F3PHPCRNodeIteratorInterface $nodes) {
$objects = array();
foreach ($nodes as $node) {
$object = $this->mapSingleNode($node);
$this->persistenceManager->getSession()->registerReconstitutedObject($object);
$objects[] = $object;
}

return $objects;
}

F3TYPO3CRFLOW3PersistenceDataMapper

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$explodedNodeTypeName = explode(':', $node->getPrimaryNodeType()->getName(), 2);
$className = str_replace('_', '', $explodedNodeTypeName[1]);
$classSchema = $this->persistenceManager->getClassSchema($className);
$objectConfiguration = $this->objectManager->getObjectConfiguration($className);

$object = $this->objectBuilder->createEmptyObject($className,
$objectConfiguration);
$this->identityMap->registerObject($object, $node->getIdentifier());

$this->objectBuilder->reinjectDependencies($object, $objectConfiguration);
$this->thawProperties($object, $node, $classSchema);
$object->FLOW3_Persistence_memorizeCleanState();


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public function createEmptyObject($objectName, F3FLOW3ObjectConfiguration
$objectConfiguration) {
$className = $objectConfiguration->getClassName();

if (!in_array('F3FLOW3AOPProxyInterface', class_implements($className))) {
throw new F3FLOW3ObjectExceptionCannotReconstituteObject('Cannot create
empty instance of the class quot;' . $className . 'quot; because it does not implement
the AOP Proxy Interface.', 1234386924);
}

$object = unserialize('O:' . strlen($className) . ':quot;' . $className . 'quot;:0:{};');
$object->FLOW3_AOP_Proxy_setProperty('objectFactory', $this->objectFactory);
$object->FLOW3_AOP_Proxy_setProperty('objectManager', $this->objectManager);
$object->FLOW3_AOP_Proxy_declareMethodsAndAdvices();

return $object;
}

F3FLOW3ObjectBuilder

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Lazy Loading
Loading a full object tree makes sense – or not

It does most of the time

If your domain model has small aggregates eager loading
makes sense

If you have expensive to create objects or a lot of smaller ones
you don’t always need, lazy loading helps

Example: displaying a list of projects doesn’t need the projects
details, just the names

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Lazy Loading
Ideally you would not think about lazy loading beyond the
addition of the @lazy annotation

In practice you need to be aware of some technical issues

In place of the real object you get a proxy, so

• you can’t use it at type hinted places

• pass it around without some thinking

Using it otherwise works as expected

After ﬁrst use the proxy will be completely gone

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The LazyLoadingProxy
public function _loadRealInstance() {
$realInstance = $this
->F3_FLOW3_Persistence_LazyLoadingProxy_population
->__invoke();
$this
->F3_FLOW3_Persistence_LazyLoadingProxy_parent
->FLOW3_AOP_Proxy_setProperty(
$this->F3_FLOW3_Persistence_LazyLoadingProxy_propertyName,
$realInstance
);

return $realInstance;
}

F3FLOW3PersistenceLazyLoadingProxy

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$dataMapper = $this; // make available to closure...
$objectStorage = new F3FLOW3PersistenceLazyLoadingProxy(
$parent,
$propertyName,
function() use ($proxyNode, $dataMapper) {
$objectStorage = new SplObjectStorage();
$itemNodes = $proxyNode->getNodes();
foreach ($itemNodes as $itemNode) {
$objectNode = $itemNode->getNode('ﬂow3:object');
if ($objectNode->getPrimaryNodeType()->getName() ===
F3TYPO3CRFLOW3PersistenceBackend::NODETYPE_OBJECTPROXY) {
$object = $dataMapper->mapObjectProxyNode($objectNode);
} else {
$object = $dataMapper->mapSingleNode($objectNode);
}
$objectStorage->attach($object);
}
return $objectStorage;
}
);


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Node structure
PHP has more data structures than a content repository, e.g.

• JSR-283 deﬁnes multi-valued properties without keys and
without stable ordering

• Arrays in PHP have keys and order that are stable and might
be important for your code

Thus we do some more mapping to node structures

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Questions!

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Links
FLOW3
http://ﬂow3.typo3.org/

TYPO3CR
http://forge.typo3.org/projects/show/package-typo3cr

JSR-283
http://jcp.org/en/jsr/detail?id=283

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Flickr photo credits:
megapixel13 (barcode), rmrayner (ring), Ducatirider (grapes), Here’s Kate (book shelf)
Pumpkin pictures:
http://ptnoticias.com/pumpkinway/

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Transparent Object Persistence (within FLOW3)

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