Understanding DoctrineJuti Noppornpitak

Today’s Menu

• What is object relational mapping?

• How is Doctrine designed? • Change Tracking Policy • Proxies and Lazy loading • DBAL or ORM?

• Cascading • Doctrine Event System • Second Level Cache • Metadata Cache* • Query Cache* • Result Cache*

Juti NoppornpitakInstaclick Inc., shiroyuki.com, @shiroyuki

What is object relational mapping?

How is Doctrine designed?

Object-relational impedance mismatchPROBLEM

Data Mapper Pattern

DESIGN

Unit of Work

DESIGN

Repository Pattern

DESIGN

Source: http://msdn.microsoft.com/en-us/library/ff649690.aspx

Now, it is time for the entrée.

Change Tracking Policy

Implicit change tracking policy

known as persisting by (UnitOfWork’s) reachability

This meansEntityManager’s persist method is disregarded and

everything reachable/managed by the entity manager, including an initialized proxy, will be persisted

automatically.

Explicit change tracking policy

This meansthe code has to explicitly persist to save the data.

Notify change tracking policy

This meansthe code has full control to explicitly tell UnitOfWork

whether or not the entity is updated. !

So, even if there is an update, the change can be discarded as the notify method says there is no change.

Proxies and Lazy Loading

Everything is a proxy.

What does it mean?

Suppose you have m entities, named a1, a2, ... and am. During the course of code execution,

we make a lot of queries. Each query makes at least one proxy per entity in the result set.

Hence, the number of proxies will be around c×m proxies.

Beside retrieving the ID of the proxy, retrieving or defining properties of a proxy always triggers the proxy loading if the proxy is set for lazy loading.

!In this situation, it might lead to making around

cm queries by the end of the execution.

Solutions

Solution 1Multiple SELECTs (ORM/DQL)

SELECT u, g FROM User u JOIN u.groups g WHERE u.id = :id

Solution 2SELECT PARTIAL (ORM/DQL)

SELECT PARTIAL u.{id, name} FROM User u WHERE u.id = :id

SELECT PARTIAL u.{id, name}, PARTIAL g.{id, name} FROM User u JOIN u.groups g WHERE u.id = :id

or

Solution 3Set the fetch mode to “eager”.

But it is not recommended.

Why?

So, please do not try to use the “eager” mode.

DBAL or ORM?

Doctrine 2Common bundle, DBAL bundle and ORM bundle

ORM is convenientbut we have to exchange resource for the convenience.

Fetching as a hydrate arrayinstead of an object graph.

Database Abstract and Access Layer (DBAL)The thin runtime layer to low-level APIs, such as, PDO.

When should I use DBAL?

Why should I use the ORM first?

ascadingC

Supported cascading operations

DELETE, DETACH, MERGE and PERSIST

Cascade on delete

EDOCTRINE VENT SYSTEM

Event Listeners

Entity ListenersNew in Doctrine ORM 2.4

LifeCycle Event Callbacks

It is the ugliest but best of all.

Let’s leap into the

future

SECOND LEVEL CACHE

How is the second level cache designed?for more information, see https://github.com/doctrine/doctrine2/pull/808

The cache servers usually have faster read/write access

than database servers.

The cache servers only need to search from the smaller data set. This means it is faster to find the

queried data.

So, one obvious benefit of using the second level cache is that we

reduce the access to the database.

A few more things...

Other kinds of cacheThey are not really visible but worth to mention.

Metadata Cache

Query Cache

Result Cache

CONCLUSION

THE END

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