What is Slick and why we use it? Mark van der Tol

Why we moved to SQL MongoDB has No joins or referential integrity No transactions Max element size for index Advantages PostgreSQL has Better indexes Better tooling Strict schema 2

Problem faced with MongoDB Query unseen alerts for users Data: { "message": "Example alert", "seenBy": [...] } Query: { "seenBy": { "$ne": "user" } } Max element size for indexed elements: 1 KB 3

Trivial in SQL SELECT message FROM alerts WHERE id NOT IN ( SELECT messageId FROM views WHERE user = "user" ) 4

MongoDB We keep using Mongo for statistics data Easier to shard/replicate No schema enforcement 5

What is Slick Database query library for Scala Table mapping Strongly typed Collection like syntax 6

Available for DB2* Derby/JavaDB H2 HSQLDB/HyperSQL Microsoft Access Microsoft SQL Server MySQL Oracle* PostgreSQL SQLite *Requires subscription for production use 7

Database connection import scala.slick.driver.PostgresDriver.simple._ import Database.threadLocalSession Database.forURL("jdbc:postgresql://…", driver = "org.postgresql.Driver") withSession { //session is now implicitly available in thread-local storage } Database.forURL("jdbc:postgresql://…", driver = "org.postgresql.Driver") withTransaction { //session is now implicitly available in thread-local storage } 8

Table definition object CoffeeTable extends Table[(String, BigDecimal, Int)]("COFFEE") { def name = column[String]("NAME", O.PrimaryKey) def price = column[BigDecimal]("PRICE") def sales = column[Int]("SALES") def * = name ~ price ~ sales } 9

Simple SELECT query val minPrice: BigDecimal = 1.0 val query = for { c <- CoffeeTable if (c.price >= minPrice) } yield (c.name) val names = query.list 10

Table definition for Case class case class Coffee (name: String, price: BigDecimal, sales: Int) object CoffeeTable extends Table[Coffee]("coffee") { def name = column[String]("NAME", O.PrimaryKey) def price = column[BigDecimal]("PRICE") def sales = column[Int]("SALES") def * = name ~ price ~ sales <> (Coffee, Coffee.unapply _) } 11

Simple SELECT query val query = for { c <- CoffeeTable } yield (c) val coffees = query.list 12

SELECT query with join val query = for { p <- PersonTable c <- CoffeeTable if (p.favoriteCoffee === c.name) } yield (p.name, c.name, c.price) 13

INSERT query CoffeeTable.insert( Coffee("Java", 2.50, 0) ) 14

UPDATE/DELETE query val query = for { c <- CoffeeTable if (c.price < 1.50) } yield (c.price) query.update(1.50) query.delete 15

Plain SQL queries val query = StaticQuery.query[BigDecimal, (String, Int)]( """select c.name, c.sales from coffees c where c.price < ?""" ) 16

Features not shown Queries with parameters Extensible: Add own types and functions "Direct embedding" 17

Features Query library that stays close to SQL Hides dbms specific syntax Prevents SQL-injections Many checks compile time 18

Disadvantages DSL not always intuitive Difficult compile errors Focus on single thread usage Not very comprehensive documentation 19

Multi-threaded use workaround val session = Database.forURL("jdbc:…", driver = “…").createSession() session.conn.setAutoCommit(false) //prevent Slick from creating transactions itself session.asInstanceOf[BaseSession].inTransaction = true … session.conn.commit() session.close() 20

Resources Slick: Sheets: 21

THANK YOU 22