Feedbacks from the trenches

François ARMAND @fanf42 - 2016-10

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OBJECT MAPPING

PURESQL

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Love SQL ?

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Who’s talkin’ for why?

● 10 years of Scala

● CTO @Normation● Lead-dev on Rudder● chose Scala 7y ago for Rudder

Continuous Configuration for Effective ComplianceFrançois ARMAND / @fanf42

● 10 years of Scala

● CTO @Normation● Lead-dev on Rudder● chose Scala 7y ago for Rudder

Continuous Configuration for Effective Compliance

Squeryl

François ARMAND / @fanf42

Who’s talkin’ for why?

● 10 years of Scala

● CTO @Normation● Lead-dev on Rudder● chose Scala 7y ago for Rudder

Continuous Configuration for Effective Compliance

SquerylJdbcTemplate

François ARMAND / @fanf42

Who’s talkin’ for why?

But what ?

● 10 years of Scala

● CTO @Normation● Lead-dev on Rudder● chose Scala 7y ago for Rudder

Continuous Configuration for Effective Compliance

SquerylJdbcTemplate

François ARMAND / @fanf42

Who’s talkin’ for why?

Slick 3 ?

● Fairly popular, ~ default choice in 2016 for Scala world

● Let’s test it ! ⇒ ported ~ 50% of Rudder code to it.

● Fairly popular, ~ default choice in 2016 for Scala world

● Let’s test it ! ⇒ ported ~ 50% of Rudder code to it.

● Does not work for us :● Feels magic and ORM-y, with *Surprises*

○ in generated SQL■ you can’t precisely control it (that’s the point)

○ in performance (using path of least resistance)■ ex: run-time compilation for EACH request in the path of least resistance

○ with lift embeding type ■ i.e working with Rep[MyClass] in place of MyClass

● An awful lot of boilerplate

Slick 3 ?

Doobie ?

Use Doobie. It’s GREAT.

Doobie

Use Doobie. It’s GREAT.

Questions ?

Doobie

Use Doobie.It’s GREAT.Doobie

● A pure functional, principled database access layer for Scala

Use Doobie.It’s GREAT.Doobie

● A pure functional, principled database access layer for Scala

● Mapping is a joy (actually make me smile)

Use Doobie.It’s GREAT.Doobie

● A pure functional, principled database access layer for Scala

● Mapping is a joy (actually make me smile)

● No surprises - particularly in performances and optimization

Use Doobie.It’s GREAT.Doobie

● A pure functional, principled database access layer for Scala

● Mapping is a joy (actually make me smile)

● No surprises - particularly in performances and optimization

● Rob Norris (@tpolecat) is über nice and helpful

Use Doobie.It’s GREAT.Doobie

● A pure functional, principled database access layer for Scala

● Mapping is a joy (actually make me smile)

● No surprises - particularly in performances and optimization

● Rob Norris (@tpolecat) is über nice and helpful

● It actually makes me like SQL ○ (it tooks 15 years, and PostgreSQL helps a lot)

Use Doobie.It’s GREAT.

● A pure functional, principled database access layer for Scala

● Mapping is a joy (actually make me smile)

● No surprises - particularly in performances and optimization

● Rob Norris (@tpolecat) is über nice and helpful

● It actually makes me like SQL ○ (it tooks 15 years, and PostgreSQL helps a lot)

Doobie

A principled database access layer for Scala

● everything is a value● standard functional programming idioms apply● Clear separation of concepts

○ (I won’t talk about Free Monad - oups)

Mapping just works. No boilerplate.

Mapping just works. No boilerplate.

Mapping just works. No boilerplate.

Mapping just works. No boilerplate.

Mapping just works. No boilerplate.

Mapping just works. Returns what you want.

No surprises - Sane (performant) defaults

● The exact, 50 lines if you want,SQL queries you want to write.

● PreparedStatement by default.● Batch updates are given.

● Comparison with JDBC

Rob Norris @tpolecat

(like, he produced working code for SQLXML mapping. At 3 a.m. Just for me)(OK, 3 a.m for my timezone. But still :)

is extremely nice and helpful

actually likes SQL

Update 0.4.0: rainbows and wonders

● Fragments○ https://tpolecat.github.io/doobie-scalaz-0.4.0/08-Fragments.html ○ Doobie 0.4.0 add fragments, which allows to safely build and factor out part of requests

(typically: “select column1, …, column42 in the_table”)

● Logging○ https://tpolecat.github.io/doobie-scalaz-0.4.0/10-Logging.html ○ Allows to log queries… based on conditions ! Plus, access to full, fine grained timing.

■ “only the one for which you get an error from Database”■ Or “all the queries taking more than 200ms” !

○ über easy to connect with your logging framework

● Cats or Scalaz○ now, you can choose!

Yes. Really.

Savant word for

“Makes you love SQL - No surprise, it just works”

Questions ?

The End

References

● Book of Doobie : https://tpolecat.github.io/doobie-0.3.0/00-index.html

● Really nice presentation of concepts and use of Free Monad:○ SBTB 2015: Rob Norris, Programs as Values: JDBC Programming with Doobie:

https://www.youtube.com/watch?v=M5MF6M7FHPo

● https://twitter.com/tpolecat

● https://gitter.im/tpolecat/doobie● The faq is pretty cool: https://tpolecat.github.io/doobie-0.3.0/15-FAQ.html (“in”

clause, outer join, pure SQL strings and more)

● Rudder is full of examples, feel free to read files (importing Doobie) in: https://github.com/Normation/rudder/tree/branches/rudder/4.0/rudder-core/src/main/scala/com/normation/rudder/repository/jdbc

Question: testing mapping in the repl ?

This is integrated with testing frameworks, in particular scalacheck

Question: more typed, safer queries ?

● Some things are coming in Doobie 0.4.0 !○ but nothing is fixed for now

○ [update] Actually, was reported post 0.4.0

● I sum-up all the feedback/ideas I get at Scala.io 2016 here: https://github.com/tpolecat/doobie/issues/375

Question: variables number or parameters?

How I deal with a query whose number of parameter is know at runtime ?Doobie has several level of API:

● sql””” …. “”” : the simplest, but also the less flexible● Query/Query0: give a return type, a type for parameters, and a string for query: allows to build

queries by string concatenation (ideal for porting from JDBC)

● HC: “high interface”: allows to add parameter by index, “à la” JDBC, but typed. ○ full, complexe example on next page that adapt a query at runtime based on user

parameters, and use HC● and a low level interface, where all JDBC ugliness is exposed

Question: variables number or parameters?

} Request depends of parameters of the function

Query is a pure string built with concatenation

Dynamically set parameters

with HPS & HC

Question: retrieving variable depths of

dependent objects?

One big question in data persistance layer is to manage the depth in the dependency graph of object you are going to retrieve. Typically, with an employee having a property “manager”, which is an ID in DB but also (of course) an employee, how I manage to get only the first employee with the manager ID ? The first employee with the full employee manager ? And his manager ?

Rob Norris gave a super talk exactly on that subject at ScalaWorld 2016:

● “Pure Functional Database Programming with Fixpoint Types “○ slides: http://tpolecat.github.io/presentations/sw2016/slides.html#1○ video: https://www.youtube.com/watch?v=7xSfLPD6tiQ

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