orm - tuningujemy podejście do mapowania
TRANSCRIPT
ORM and..Bad habits
Patryk Szlagowski
Patryk SzlagowskiBackend Developer at Logisfera Nova - lsn.io
@abdulklarapl
Captain at FunkyMonkeyLabs
1. ORM - what is it?
2. Problem 1 - greedy fetching3. Problem 2 - „lets map everything”
4. Performance table5. Conclusions
6. Conclusions - moar
1. ORMIn one picture
ORMDB applicationDBAL*
/** * @Route("/", name="homepage") */public function indexAction(Request $request) { return $this->render('default/index.html.twig', array( 'news' => $this->getDoctrine() ->getRepository('AppBundle:Post') ->findAll() )); }
2. Problem 1 - greedy fetching
/** * @return Post[] */public function getAll() { $qb = $this->createQueryBuilder("post"); $qb ->select("post, author, role, category, comments, commentsAuthor, commentsAuthorRole") ->join("post.category", "category") ->join("post.author", "author") ->join("author.role", "role") ->join("post.comments", "comments") ->join("comments.author", "commentsAuthor") ->join("commentsAuthor.role", "commentsAuthorRole"); return $qb->getQuery()->getResult(); }
That is nice. But wait.. How is possible, that results can be mapped to relations from this?
Let’s add custom method in repository and control the joins
2. Problem 1 - greedy fetching
2. Problem 1 - greedy fetching
SELECT {fields}FROM post p0_INNER JOIN dictionary_item d1_ ON p0_.category_id = d1_.idINNER JOIN person p2_ ON p0_.author_id = p2_.idINNER JOIN dictionary_item d3_ ON p2_.role_id = d3_.idINNER JOIN COMMENT c4_ ON p0_.id = c4_.post_idINNER JOIN person p5_ ON c4_.author_id = p5_.idINNER JOIN dictionary_item d6_ ON p5_.role_id = d6_.id
That is I expected. 3 rows for 1 post (3 comments). ORM mapped columns to many objects, grouped by primary key.
But let’s imagine, what if we have 100 records (A) with relation to B (10 records each) AND B-C (with another 10 records for each B)? 10000 records to map.
2. Problem 1 - greedy fetchingWhat’s going on?
What if..I tell you, that you can get all of the rows by one query, without multiply results rows number?
IMPOSSIBRU
Cons• PostgreSQL • JSON functions • complicated query • slower than simple
query
Pros
• JSON response • whole object in one row • what you see in results,
it’s what you get in app
SELECT array_to_json( array_agg( row_to_json({alias}) ) )FROM ( {subquery}) AS {alias}
SELECT array_to_json(array_agg(row_to_json(results)))FROM ( SELECT post.id, post.create_date, post.content, post.title, (SELECT row_to_json(author) FROM ( SELECT person.*, ( SELECT row_to_json(role) FROM ( SELECT * FROM dictionary_item di WHERE di.id = person.role_id ) AS role ) AS role FROM person WHERE person.id = post.author_id ) as author) AS author, ( SELECT row_to_json(category) FROM dictionary_item category WHERE category.id = post.category_id ) as category, ( SELECT array_to_json(array_agg(row_to_json(comments))) FROM ( SELECT comment.title, comment.content, ( SELECT row_to_json(comment_author) FROM ( SELECT person.*, ( SELECT row_to_json(role) FROM ( SELECT * FROM dictionary_item di WHERE di.id = person.role_id ) AS role ) AS role FROM person WHERE person.id = comment.author_id ) AS comment_author ) AS author FROM comment where comment.post_id = post.id ) AS comments ) as commentsFROM post) AS results
3. Problem 2 - results mapping
ORMDataSource response
application model
REST response
In most cases
for what?
3. Problem 2 - results mapping
DataSource response
array/hashmap response REST response
In most cases
Built-in findAll function
Simple query with joins, mapped to
objects
array_to_json query, mapped to objects
array_to_json query, no mapping, return
in REST Api
query time 2326ms 52ms 101ms 111ms
memory usage 82MB 51MB 33.5MB 17.2MB
total (with render) time 7464ms 2100ms 1755ms 364ms
number of queries 4405 1 1 1
4. All about performance
* tested with 400 posts, 10 comments per post, one author per comment, author per post, label per category
5. ConclusionsQuery buildersQuery builders
$this->repository->findAll()
4405
trolololovs
$this->repository->customFindAll()
1
1. Maybe we should start using aggregating functions to get data from DB
2. If you don’t have to to transform DB response to object - don’t do it
3. Don’t use built-in functions such as findBy, findAll, findOne, sth, sth
4. Write your own functions with joins, groups to take control over the query
5. Remember about lazy loading
6. Conclusions
Thank youI want to talk with you