Hi!

I'm Marco!

Ocramius

Doctrine Project

A group of persistence-oriented libraries for PHP

We are looking for contributors!

(Must be prepared to take unpopular decisions)

Doctrine ORM

A JSR-317 / Hibernate inspired Object Relational Mapper

Doctrine 2 ORM
Best Practices

Know your enemy

Know your enemy tools

Read the Documentation

Knowledge is Power

When is an ORM the appropriate tool?

Who is Doctrine ORM for?

OLTP

DDD

Fast prototyping

OO-first

Who is Doctrine ORM NOT for?

Dynamic data structures

Reporting

That's what SQL is for

It's a QUERY language, after all

Where do we start?

Entities (of course)

Entities should work without the ORM

Entities should work without the DB

Entities (mostly) represent your domain

The Database is just saving things

Design entities first

Define the Database after modeling your domain

Define Mappings after designing the Entities

Designing Entities


class User {
    private $username;
    private $passwordHash;

    public function getUsername() :string {
        return $this->username;
    }

    public function setUsername(string $username) {
        $this->username = $username;
    }

    public function getPasswordHash() : string {
        return $this->passwordHash;
    }

    public function setPasswordHash(string $passwordHash) {
        $this->passwordHash = $passwordHash;
    }
}

Entities are NOT typed arrays

Entities have Behavior

Entity
internal State design
is Irrelevant

You can deal with state after designing the API

Designing State-first leads to terrible coupling 


class User {
    private $banned;
    private $username;
    private $passwordHash;

    public function toNickname() : string {
        return $this->username;
    }

    public function authenticate(
        string $pass, callable $checkHash
    ) : bool {
        return $checkHash($pass, $this->passwordHash)
            && ! $this->hasActiveBans();
    }

    public function changePass(string $pass, callable $hash) {
        $this->passwordHash = $hash($pass);
    }
}

No behavior
=
no need for the ORM

Respect the LOD


class User
{
    // ...
    public function hasAccessTo(Resource $resource) : bool
    {
        return (bool) array_filter(
            $this->role->getAccessLevels(),
            function (AccessLevel $acl) use ($resource) : bool {
                return $acl->canAccess($resource)
            }
        );
    }
}


class User
{
    // ...
    public function hasAccessTo(Resource $resource) : bool
    {
        return $this->role->allowsAccessTo($resource);
    }
}

More expressive

Easier to test

Less coupling

More flexible

Easier to refactor

Disallow
Collection access
from outside the Entity 


class User
{
    private $bans;

    public function getBans() : Collection {
        return $this->bans;
    }
}


public function banUser(Uuid $userId)
{
    $user = $this->repository->find($userId);

    $user->getBans()->add(new Ban($user));
}

Keep Collections hidden in your Entities


class User
{
    private $bans;

    public function ban() {
        $this->bans[] = new Ban($this);
    }
}


public function banUser(Uuid $userId)
{
    $user = $this->repository->find($userId);

    $user->ban();
}

Entity Validity

Entities should always be valid

Invalid state should be in a different object

(You may need a DTO)

(Also applies to Temporary State)

Stay valid after __construct

(Regardless of the DB)

Named constructors are OK

Avoid setters

Avoid coupling with the Application Layer 


class UserController
{
    // form reads from/writes to user entity (bad)
    public function registerAction()
    {
        $this->userForm->bind(new User());
    }
}


class UserController
{
    // coupling between form and user (bad)
    public function registerAction()
    {
        $this->em->persist(User::fromFormData($this->form));
    }
}

Form components break Entity Validity

Both Symfony\Form and Zend\Form are terrible

(For this use-case)

Use a DTO instead

Avoid Lifecycle Callbacks

Lifecycle Callbacks are a Persistence Hack

Lifecycle Callbacks are supposed to be the ORM-specific serialize and unserialize

Don't use Lifecycle Callbacks for Business Logic/Events

Avoid auto-generated identifiers

Your db operations will block each other

You are denying bulk inserts

You cannot make multi-request transactions

Your object is invalid until saved

Your object does not work without the DB

Use UUIDs instead

Don't forget that a UUID is just a 128 bit integer!


public function __construct()
{
    $this->id = Uuid::uuid4();
}

auto_increment is abused for sorting

Are you looking for a DATETIME field instead?

Avoid derived primary keys

You are just normalizing for the sake of it

Does your domain really NEED it?

Avoid composite primary keys

Any reason to not use an unique constraint instead?

Do they make a difference in your domain?

Favour immutable entities

Or append-only data-structures


class PrivateMessage
{
    private $from;
    private $to;
    private $message;
    private $read = [];

    public function __construct(
        User $from,
        User $to,
        string $message
    ) {
        // ...
    }

    public function read(User $user) {
        $this->read[] = new MessageRead($user, $this);
    }
}


class MessageRead
{
    private $user;
    private $message;

    public function __construct(User $user, Message $message)
    {
        $this->id      = Uuid::uuid4();
        $this->user    = $user;
        $this->message = $message;
    }
}

Immutable data is simple

Immutable data is cacheable (forever)

Immutable data is predictable

Immutable data enables historical analysis

You may want to look at Event Sourcing...

Avoid Soft-Deletes

Soft Deletes are a broken idea

Soft Deletes come from an era where keeping everything in a single DB was required

Soft Deletes
break
immutability

Soft Deletes
break
Data integrity

(and therefore validity)

Soft Deletes can usually be replaced with more specific domain concepts

Mapping driver choice

Use Annotations in private packages

Use XML Mappings in public packages

Lazy or Eager?

Eager Loading is Useless

Extra Lazy indicates high risk areas

We reach the limits of the ORM

Careful about performance/transaction size!

Avoid bi-directional associations

bi-directional associations are overhead

Code only what you need for your domain logic to work

Hack complex DQL queries instead of making them simpler with bi-directionality

Use custom repositories for improved expressiveness 


final class UserRepository
{
    public function findUsersThatHaveAMonthlySubscription()
    {
        // ... INSERT DQL/SQL HELL HERE ...
    }
}

Query Functions are better than repositories 


final class UsersThatHaveAMonthlySubscription
{
    public function __construct(EntityManagerInterface $em) {
        // ...
    }

    public function __invoke() : Traversable
    {
        // ... INSERT DQL/SQL HELL HERE ...
    }
}

Repositories are Services

So are Query Functions

Avoid ObjectManager#getRepository()

It is a ServiceLocator

It causes the same problems of the ServiceLocator

Inject Repositories instead

Separate MyRepository#get() and MyRepository#find()

MyRepository#find() can return null

MyRepository#get() cannot return null


final class BlogPostRepository
{
    // ...

    public function getBySlug($slug) : BlogPost
    {
        $found = $this->findOneBy(['slug' => (string) $slug]);

        if (! $found) {
            throw BlogPostNotFoundException::bySlug($slug);
        }

        return $found;
    }
}

Using a get() method that throws,
you can simplify error logic

Avoid 2pc

Keep transactions unrelated

Use ObjectManager#clear() between different ObjectManager#flush() calls

Different boundaries
=
Different transactions

Communicate between boundaries via identifiers,
not object references

Keep Normalization under control

Keep Normalization (freaks) under control

You may need to gag your DBAs...

Or get them to understand your needs

Academic and practical knowledge may differ

What about Performance?

Know how the ORM is structured

EntityManager

UnitOfWork

Metadata Drivers

DQL

Repositories

Second Level Cache

Profile these hotspots

Measuring is the only way

There are other talks about this...

RECAP

Domain First

Do not normalize without a need for it

Otherwise, you're digging your own grave!

Consider using Separate DBs

Transactional Data
!=
Reporting Data

Thanks!

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