Schrödinger's SQL

The SQL inside the ORM/Builder box

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Claudio Zizza

Developer for 20 years
(Currently PHP)

Organizing PHP Usergroup Karlsruhe

Part of Doctrine: doctrine-project.org
Twitter: @SenseException
Mastodon: @SenseException@phpc.social

Who has a big customer-project without a database?

Microsoft Access 2000

S E Q UE L

Structured Query Language

ISO/IEC 9075

  • SQL-86 (or SQL-87)
  • SQL-89
  • SQL-92
  • SQL:1999
  • SQL:2003
  • SQL:2006
  • SQL:2008
  • SQL:2011
  • SQL:2016
  • SQL:2019

    SELECT firstname, name FROM address_book ORDER BY name;
            

Select firstname and name from address book and order them by name

id firstname name
1 John Doe
2 Jane Doe
3 Leo Part

    SELECT firstname, name FROM address_book GROUP BY name;
            

ERROR: column "address_book.firstname" must appear in the GROUP BY clause or be used in an aggregate function

It's a PostgreSQL database.

No!

Yes!

Ooooh...

Know your database!

How did you learn SQL?


    $pdo = new PDO('mysql:dbname=bar;host=127.0.0.1');

    $statement = $pdo->query('SELECT id, name FROM foo');

    $result = $statement->fetchAll(PDO::FETCH_CLASS, Foo::CLASS);

    foreach ($result as $foo) {
        echo $foo->getId() . ' contains name ' . $foo->getName() . PHP_EOL;
    }

            

Entity


    use Doctrine\ORM\Mapping as ORM;

    #[ORM\Table(name: 'foo')]
    #[ORM\Entity]
    class Foo
    {
        #[ORM\Column(type: 'integer')]
        #[ORM\Id]
        #[ORM\GeneratedValue(strategy: 'AUTO')]
        private int $id;

        #[ORM\Column(type: 'string')]
        private string $value;

        // public function __construct(string $value)
        // public function setValue(string $value) : void
        // ...
    }
            

Insert new entity


    $entity = new Foo('value');

    $entityManager->persist($entity);

    $entityManager->flush();
            

DQL or find()


    SELECT e FROM Foo e WHERE e.id = 42
            

    $foo = $entityManager->find(Foo::class, 42);
            

Congratulations

ORM

+

You have doubled your problems

ORM is awesome, but

before it was:

  • Know how to query
  • OOP boilerplate code

Now it is:

  • Know how queries look like
  • Know when queries happen
  • Know how to query
  • No full SQL power due to DB compatibility

Know when queries happen

Insert new entity


    $entity = new Foo('value');

    $entityManager->persist($entity);

    $entityManager->flush(); // <-- There's SQL somewhere in there
            

Update entity (default tracking policy)


    $entity = $entityManager
        ->find(Foo::class, 42); // <-- There's SQL somewhere in there

    $entity->setValue('new value');

    $entityManager->flush(); // <-- There's SQL somewhere in there
            

What Unit Of Work does


    $entity = $entityManager->find(Foo::class, 42);
    
    // ... sooo much code
    
    $entity = $entityManager->find(Foo::class, 42); // <-- No SQL query
            

Which language?


    $de = new Language('de');
    $en = new Language('en');
    $it = new Language('it');
    $entityManager->persist($de);
    $entityManager->persist($en);
    $entityManager->persist($it);

    $movie = new Movie('The Mutex');
    $movie->setLanguages([$de, $en, $it]);
    $entityManager->persist($movie);
    $entityManager->flush();

    $movie = $entityManager->createQuery(
            "SELECT m, l FROM Movie m
            JOIN m.languages l
            WHERE l.iso6391 = 'it' AND m.name = 'The Mutex'"
        )
        ->getResult();

    $movie[0]->getLanguages();
            

All languages

  • de
  • en
  • it

Clear EntityManager/Unit Of Work


    $entityManager->persist($movie);
    $entityManager->flush();

    $entityManager->clear(); // <-- Clear enities from the EntityManager/Unit Of Work

    $movie = $entityManager->createQuery(
            "SELECT m, l FROM Movie m
            JOIN m.languages l
            WHERE l.iso6391 = 'it' AND f.name = 'The Mutex'"
        )
        ->getResult();

    $movie[0]->getLanguages();
            

Lazy vs. Eager Loading


    class Foo
    {
        // ...

        /**
         * @var Bar[]
         *
         * Use LAZY or EAGER in fetch
         */
        #[ORM\OneToMany(targetEntity: 'Bar', mappedBy: 'foo', fetch: 'LAZY')]
        private $bars;

        // ...
    }
            

Lazy vs. Eager Loading


    $foos = $entityManager->getRepository(Foo::class)
        ->findAll();

    foreach ($foos as $foo) {
        foreach ($foo->getBars() as $bar) {
            // do stuff
        }
    }
            

Same code, different SQL

Lazy

  -- findAll() returns 3 Foo entities
  SELECT t0.id AS id_1, t0.name AS name_2 FROM foo t0
  -- Each query is one iteration for getting the Bar relations
  SELECT t0.id AS id_1, t0.name AS name_2, t0.foo_id AS foo_id_3 FROM bar t0 WHERE t0.foo_id = 1
  SELECT t0.id AS id_1, t0.name AS name_2, t0.foo_id AS foo_id_3 FROM bar t0 WHERE t0.foo_id = 2
  SELECT t0.id AS id_1, t0.name AS name_2, t0.foo_id AS foo_id_3 FROM bar t0 WHERE t0.foo_id = 3
            
Eager

  -- findAll() returns 3 Foo entities and joins the bar relation
  SELECT t0.id AS id_1, t0.name AS name_2, t3.id AS id_4, t3.name AS name_5, t3.foo_id AS foo_id_6
      FROM foo t0
      LEFT JOIN bar t3 ON t3.foo_id = t0.id
            

Know how queries look like

Explicit join - One query


SELECT f, b FROM Entity\Foo f JOIN f.bars b
            

SELECT f0_.id AS id_0, f0_.name AS name_1, b1_.id AS id_2, b1_.name AS name_3, b1_.foo_id AS foo_id_4
    FROM foo f0_
    INNER JOIN bar b1_ ON f0_.id = b1_.foo_id
            

Why should I care about how SQL looks like?


    SELECT q FROM Entity\Qux q WHERE q.city = 'Hahnland'
            

Full table scan

Index scan


    select * from qux WHERE city = 'Hahnland';
            

Before

Next release

You can't ignore indices

Slow SQL queries

  • Need more resources
  • May lock rows / Waiting queries

DQL is not SQL!

DBAL QueryBuilder


    $queryBuilder->where('f.id = 1')
        ->select('f.name', 'f.id', 'b.name as bname', 'q.stuff')
        ->leftJoin('f', 'bar', 'b', 'b.foo_id = f.id')
        ->from('foo', 'f')
        ->orWhere('f.id = 2')
        ->leftJoin('f', 'qux', 'q', 'q.foo_id = f.id'); // join order?

    if ($yolo) {
        $queryBuilder->andWhere('q.moreStuff = true');
    }
            

SQL is much more powerful

Window Function


    SELECT name, department,
        SUM(revenue) OVER (PARTITION BY department ORDER BY name)
        FROM company;
            
name department SUM
Albert sales 1200
Zoe sales 1200
Angela development 1804

It's that new MySQL 8 feature

It's a SQL 2003 standard

Values List


    VALUES ('value1', 42, 1.8), ('value2', 12, 9);
            

Values List in DB Versions

  • PostgreSQL: Yes - 8.2 (and earlier)
  • MariaDB: Yes - 10.3
  • MySQL: 8.0.19 (But with ROW syntax)

JSON

MySQL/MariaDB


    SELECT JSON_OBJECT('a', name, 'b', number) AS jayson FROM foo;
            

PostgreSQL


    SELECT JSON_BUILD_OBJECT('a', name, 'b', number) AS jayson FROM foo;
            
jayson
{"a": "value1", "b": 42}

Common Table Expression (CTE)


    WITH bar (col1, col2) AS (SELECT id, content FROM foo)

    SELECT * FROM bar;
            
id parent_id name
1 NULL A
2 NULL B
3 NULL C
4 2 B-1
5 1 A-1
6 2 B-2
7 1 A-2
8 5 A-1-1
9 5 A-1-2
10 8 A-1-1-1

With Recursive


    WITH RECURSIVE cat AS (
        SELECT * from category WHERE name = 'A'
        UNION ALL
        SELECT cat_recursive.* from category as cat_recursive
            JOIN cat AS parent ON parent.id = cat_recursive.parent_id
    )
    SELECT * FROM cat;
            

With Recursive

id parent_id name
1 NULL A
5 1 A-1
7 1 A-2
8 5 A-1-1
9 5 A-1-2
10 8 A-1-1-1

This was just the tip of the iceberg

unsplash-logo Annie Spratt

Native Query (ResultSetMapping)


    // Example with PostgreSQL
    $rsm = new ResultSetMapping();
    $rsm->addEntityResult(Foo::class, 'f');
    $rsm->addFieldResult('f', 'column1', 'id');
    $rsm->addFieldResult('f', 'column2', 'name');
    $rsm->addFieldResult('f', 'column3', 'comment');

    $sql = "VALUES (5, 'foo', 'It is foo.'), (6, 'bar', 'It is bar.');";

    $query = $this->entityManager->createNativeQuery($sql, $rsm);

    $foos = $query->getResult();
            

SQL fiddles

SQL books

Thank you

What are your questions?