Working with Objects

Understanding

In this chapter we will help you understand the DocumentManager and the UnitOfWork. A Unit of Work is similar to an object-level transaction. A new Unit of Work is implicitly started when a DocumentManager is initially created or after DocumentManager#flush() has been invoked. A Unit of Work is committed (and a new one started) by invoking DocumentManager#flush().

A Unit of Work can be manually closed by calling DocumentManager#close(). Any changes to objects within this Unit of Work that have not yet been persisted are lost.

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$uowSize = $dm->getUnitOfWork()->size();
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$uow = $dm->getUnitOfWork();
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Persisting documents

A document can be made persistent by passing it to the DocumentManager#persist($document) method. By applying the persist operation on some document, that document becomes MANAGED, which means that its persistence is from now on managed by an DocumentManager. As a result the persistent state of such a document will subsequently be properly synchronized with the database when DocumentManager#flush() is invoked.

Example:

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$user = new User();
$user->setUsername('jwage');
$user->setPassword('changeme');
$dm->persist($user);
$dm->flush();
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The semantics of the persist operation, applied on a document X, are as follows:

• If X is a new document, it becomes managed. The document X will be entered into the database as a result of the flush operation.
• If X is a preexisting managed document, it is ignored by the persist operation. However, the persist operation is cascaded to documents referenced by X, if the relationships from X to these other documents are mapped with cascade=PERSIST or cascade=ALL.
• If X is a removed document, it becomes managed.
• If X is a detached document, the behavior is undefined.

Flush Options

When committing your documents you can specify an array of options to the flush method. You can use this to pass a write options to the underlying operations, e.g. a custom write concern.

Example:

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$user = $dm->getRepository(User::class)->find($userId);
// ...
$user->setPassword('changeme');
$dm->flush(['writeConcern' => new \MongoDB\Driver\WriteConcern(1)]);
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You can configure the default flush options on your Configuration object if you want to set them globally for all flushes.

Example:

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$config->setDefaultCommitOptions(
  ['writeConcern' => new \MongoDB\Driver\WriteConcern(1)]
);
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Removing documents

A document can be removed from persistent storage by passing it to the DocumentManager#remove($document) method. By applying the remove operation on some document, that document becomes REMOVED, which means that its persistent state will be deleted once DocumentManager#flush() is invoked. The in-memory state of a document is unaffected by the remove operation.

Example:

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$dm->remove($user);
$dm->flush();
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The semantics of the remove operation, applied to a document X are as follows:

• If X is a new document, it is ignored by the remove operation. However, the remove operation is cascaded to documents referenced by X, if the relationship from X to these other documents is mapped with cascade=REMOVE or cascade=ALL.
• If X is a managed document, the remove operation causes it to become removed. The remove operation is cascaded to documents referenced by X, if the relationships from X to these other documents is mapped with cascade=REMOVE or cascade=ALL.
• If X is a detached document, an InvalidArgumentException will be thrown.
• If X is a removed document, it is ignored by the remove operation.
• A removed document X will be removed from the database as a result of the flush operation.

Detaching documents

A document is detached from a DocumentManager and thus no longer managed by invoking the DocumentManager#detach($document) method on it or by cascading the detach operation to it. Changes made to the detached document, if any (including removal of the document), will not be synchronized to the database after the document has been detached.

Doctrine will not hold on to any references to a detached document.

Example:

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$dm->detach($document);
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The semantics of the detach operation, applied to a document X are as follows:

• If X is a managed document, the detach operation causes it to become detached. The detach operation is cascaded to documents referenced by X, if the relationships from X to these other documents is mapped with cascade=DETACH or cascade=ALL. Documents which previously referenced X will continue to reference X.
• If X is a new or detached document, it is ignored by the detach operation.
• If X is a removed document, the detach operation is cascaded to documents referenced by X, if the relationships from X to these other documents is mapped with cascade=DETACH or cascade=ALL/Documents which previously referenced X will continue to reference X.

There are several situations in which a document is detached automatically without invoking the detach method:

• When DocumentManager#clear() is invoked, all documents that are currently managed by the DocumentManager instance become detached.
• When serializing a document. The document retrieved upon subsequent unserialization will be detached (This is the case for all documents that are serialized and stored in some cache).

The detach operation is usually not as frequently needed and used as persist and remove.

Merging documents

Merging documents refers to the merging of (usually detached) documents into the context of a DocumentManager so that they become managed again. To merge the state of a document into an DocumentManager use the DocumentManager#merge($document) method. The state of the passed document will be merged into a managed copy of this document and this copy will subsequently be returned.

Example:

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$detachedDocument = unserialize($serializedDocument); // some detached document
$document = $dm->merge($detachedDocument);
// $document now refers to the fully managed copy returned by the merge operation.
// The DocumentManager $dm now manages the persistence of $document as usual.
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The semantics of the merge operation, applied to a document X, are as follows:

• If X is a detached document, the state of X is copied onto a pre-existing managed document instance X' of the same iddocument or a new managed copy X' of X is created.
• If X is a new document instance, an InvalidArgumentException will be thrown.
• If X is a removed document instance, an InvalidArgumentException will be thrown.
• If X is a managed document, it is ignored by the merge operation, however, the merge operation is cascaded to documents referenced by relationships from X if these relationships have been mapped with the cascade element value MERGE or ALL.
• For all documents Y referenced by relationships from X having the cascade element value MERGE or ALL, Y is merged recursively as Y'. For all such Y referenced by X, X' is set to reference Y'. (Note that if X is managed then X is the same object as X'.)
• If X is a document merged to X', with a reference to another document Y, where cascade=MERGE or cascade=ALL is not specified, then navigation of the same association from X' yields a reference to a managed object Y' with the same persistent iddocument as Y.

The merge operation is usually not as frequently needed and used as persist and remove. The most common scenario for the merge operation is to reattach documents to an DocumentManager that come from some cache (and are therefore detached) and you want to modify and persist such a document.

References

References between documents and embedded documents are represented just like in regular object-oriented PHP, with references to other objects or collections of objects.

Establishing References

Establishing a reference to another document is straight forward:

Here is an example where we add a new comment to an article:

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$comment = new Comment();
// ...

$article->getComments()->add($comment);
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Or you can set a single reference:

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$address = new Address();
// ...

$user->setAddress($address);
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Removing References

Removing an association between two documents is similarly straight-forward. There are two strategies to do so, by key and by element. Here are some examples:

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$article->getComments()->removeElement($comment);
$article->getComments()->remove($ithComment);
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Or you can remove a single reference:

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$user->setAddress(null);
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When working with collections, keep in mind that a Collection is essentially an ordered map (just like a PHP array). That is why the remove operation accepts an index/key. removeElement is a separate method that has O(n) complexity, where n is the size of the map.

Transitive persistence

Persisting, removing, detaching and merging individual documents can become pretty cumbersome, especially when a larger object graph with collections is involved. Therefore Doctrine provides a mechanism for transitive persistence through cascading of these operations. Each reference to another document or a collection of documents can be configured to automatically cascade certain operations. By default, no operations are cascaded.

The following cascade options exist:

• persist : Cascades persist operations to the associated documents.
• remove : Cascades remove operations to the associated documents.
• merge : Cascades merge operations to the associated documents.
• detach : Cascades detach operations to the associated documents.
• all : Cascades persist, remove, merge and detach operations to associated documents.

The following example shows an association to a number of addresses. If persist() or remove() is invoked on any User document, it will be cascaded to all associated Address documents in the $addresses collection.

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class User
{
    //...
    /**
     * @ReferenceMany(targetDocument=Address::class, cascade={"persist", "remove"})
     */
    private $addresses;
    //...
}
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Even though automatic cascading is convenient it should be used with care. Do not blindly apply cascade=all to all associations as it will unnecessarily degrade the performance of your application.

Querying

Doctrine provides the following ways, in increasing level of power and flexibility, to query for persistent objects. You should always start with the simplest one that suits your needs.

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$user = $dm->find(User::class, $id);
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$user = $dm->getRepository(User::class)->find($id);
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// All users that are 20 years old
$users = $dm->getRepository(User::class)->findBy(['age' => 20]);

// All users that are 20 years old and have a surname of 'Miller'
$users = $dm->getRepository(User::class)->findBy(['age' => 20, 'surname' => 'Miller']);

// A single user by its nickname
$user = $dm->getRepository(User::class)->findOneBy(['nickname' => 'romanb']);
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// All users with an age between 20 and 30 (inclusive).
$qb = $dm->createQueryBuilder(User::class)
    ->field('age')->range(20, 30);
$q = $qb->getQuery()
$users = $q->execute();
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$group = $dm->find(Group::class, $id);
$usersWithGroup = $dm->createQueryBuilder(User::class)
    ->field('group')->references($group)
    ->getQuery()->execute();
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$users = $dm->createQueryBuilder(User::class)
    ->field('groups')->includesReferenceTo($group)
    ->getQuery()->execute();
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