The document provides an introduction to Slick, a library for interacting with relational databases in Scala, emphasizing static typing, compositionality, and query building. It covers various aspects including connection drivers, table definitions, query execution, and examples of DSL usage for building and invoking queries. Additionally, it addresses drawbacks and resources for further learning about Slick.

1. The Slick Library
Rebecca Grenier
rebeccagrenier@gmail.com

2. Intro to Slick
 Static Typing + Compilation = Type Safety
 For-Comprehensions
 Compositionality: build complex queries out of simple
parts
@beckythebest

3. Introduction to Slick
@beckythebest

4. Slick Connection Drivers
 Oracle ($$$)
 DB2 ($$$)
 SQL Server ($$$)
@beckythebest
Note: Connection Pooling is your
responsibility
 PostgreSQL
 MySQL
 Access
 Derby
 H2
 Hsqldb
 SQLite

5. The Files Table
@beckythebest
Field Type Null
id int (10) unsigned NO
uid int (10) unsigned NO
path varchar (255) NO
filetype varchar (255) NO

6. Table Definitions:
Mapping to tuples
@beckythebest

7. Table Definitions:
Mapping to case classes
@beckythebest

8. How the 22-item
tuple Limit Affects Slick
What if your table has more than 22 columns?
Define multiple Table Classes that refer to the same table –
similar to “views”
* There is a workaround for Scala >= 2.10.3 where you can
use HList instead
@beckythebest

9. Queries in Slick
Every query starts out as a TableQuery first:
val files = TableQuery[Files]
is the equivalent of
select * from files;
(You can use .selectStatement on any query to see
the SQL for a select statment that is generated
behind the scenes)
@beckythebest

10. A Quick Full Example
val allFiles = db withSession {
implicit session =>
files.run
}
allFiles is a Vector of File case class objects
files is just the query and remains so until it is invoked
(with .run)
@beckythebest

11. Building Your Query:
Adding a Where Clause
With .filter
files.filter(_.filetype === ‘pdf’)
In SQL: select * from files where
filetype= ’pdf’
• In Slick, equals is ===
• Not-Equals is =!=
@beckythebest

12. Use Method Chaining to Add
More Clauses to Your Query
Slick: files.filter(_.filetype ===
“pdf”).filter(_.id < 20000)
SQL: select * from files where filetype=
“pdf” and id < 20000
Reminder: You are not really filtering
yet;
@beckythebest
you are building a Query.

13. Query Building
with Modifiers from Slick’s DSL
 take
files.take(5) SQL: select * from files limit 5
 Drop
files.drop(5) SQL: select * from files offset 5
 length
files.length SQL: select count(*) from files
 map
 flatMap
 sortBy SQL: sort by
@beckythebest

14. Connecting to Your Database
in Slick
Connect with Database.forURL
There is also forDriver, forName, and forDataSource
@beckythebest

15. Queries Need Sessions
Use that Database Connection to get a
Session
@beckythebest
This is a static
session

16. Just Say No to
Dynamic Sessions
AKA A non-explicit session you hope was opened earlier this
thread
Dynamic
Sessions
You can’t count on your thread having a session in an
@beckythebest
asyncronous world

17. Query Invokers
Invoker Returns
Vector of results
List of results
First result or Exception
Some(first) or None
Nothing
files.run
files.list
files.first
files.firstOption
files.execute
@beckythebest

18. Invoke a Delete Query
scala> files.deleteStatement
res5: String = delete from `files`
invoke with .delete
files.delete
@beckythebest

19. Just Delete One Record
Reduce your query with filter:
> files.filter(_.id === 56).deleteStatement
res6: String = delete from `files` where
`files`.`id` = 56
Invoked:
files.filter(_.id === 56).delete
@beckythebest

20. Insert Query Invoker
scala> files.insertStatement
res1: String = insert into `files`
(`id`,`path`,`filetype`,`uid`) values
(?,?,?,?)
invoke with +=
files += File(0, “path to file”, “type”, 333)
@beckythebest

21. Update Query Invoker
scala> files.map(_.path).updateStatement
res4: String = update `files` set `path` = ?
invoke with .update()
files.map(_.path).update(“new path to file”)
@beckythebest

22. Best Practice: Build your Query
Completely BEFORE Invoking
The commands below look similar but have very
different performance:
files.take(5).run
SQL: (select * from files limit 5)
files.run.take(5)
SQL: (select * from files) take 5
@beckythebest

23. What good is all this
Typing?
Use SQL to query the files table by fid (which is an integer)
What happens when a non-integer value gets passed in?
@beckythebest
No error?
No big deal!

24. VS. Static Typing
If you do the same thing in Slick:
We get the following error at compile time:
@beckythebest

25. Joining: Introducing The Users
Table
@beckythebest

26. Files has a new column: uid
@beckythebest

27. Joining with For-
Comprehensions
SQL: select * from
users,files where
files.uid = users.id
When invoked (with innerJoinFileUser.run) this
returns a Collection of tuples with the first item being of
type User and the second being of type File
@beckythebest

28. Where Clauses in For-
Comprehensions
 Use filter expressions instead of filters
 Example: limit to only files owned by Sarah:
@beckythebest

29. Slick also has its own Join
Methods
We just looked at this query joined with a for-comprehension:
Same query joined with innerJoin method:
@beckythebest

30. The SQL Behind the
Scenes
Joined with a for-comprehension
select x2.`uid`, x2.`name`, x2.`mail`, x2.`status`,
x3.`id`, x3.`path`, x3.`filetype`, x3.`uid` from
`users` x2, `files` x3 where x3.`id` = x2.`uid`
Joined with the innerJoin method
select x2.x3, x2.x4, x2.x5, x2.x6, x7.x8, x7.x9,
x7.x10, x7.x11 from (select x12.`id` as x3, x12.`name`
as x4, x12.`mail` as x5, x12.`status` as x6 from
`users` x12) x2 inner join (select x13.`id` as x8,
x13.`path` as x9, x13.`filetype` as x10, x13.`uid` as
x11 from `files` x13) x7 on x2.x3 = x7.x11
@beckythebest

31. Return Anything You Want
With these for-comprehension use yield to reduce the data
you want returned
Instead of yield(u, f) you could have
 yield(f)
 yield (u.name, f.path)
 yield (f.path)
@beckythebest

32. Slick Outer Joins
 You can’t do these with for-comprehensions
 f.path.? turns values into Options (there might not be
files for every user)
 f.? doesn’t work
* Remember, you can always use plain SQL with Slick
@beckythebest

33. Query Compositionality
Every query does Double
Duty:
1. Invoke to get data
2. Use as a building block for
another query
@beckythebest

34. Create Query Methods
object Files {
def byType(filetype: String) =
files.filter(_.filetype === filetype)
}
implicit session =>
Files.byType(“text/html”).list
Returns a list of HTML File case classes
@beckythebest

35. Let’s Look at the SQL Behind
That
The method itself is not a Query, but it returns a Query
scala> filesByType.selectStatement
ERROR
scala> filesByType(“pdf").selectStatement
res3: String = select * from `files` x2 where
x2.`filetype` = ‘pdf'
@beckythebest

36. Composing Queries out of
Queries
object Users {
def userPDFS(email: String) = for {
u <- users if u.email === email
f <- Files.byType(“pdf”) if f.uid ===
u.id
} yield (f)
}
@beckythebest

37. Quick Look at the SQL
scala>
userPDFS("sarah@eatingwell.com").selectStatement
res0: String = select files`id`, files.`path`,
files.`filetype`, files.`id` from `users`,
`files` where ((users.`mail` =
'sarah@eatingwell.com') and (files.`filetype` =
'application/pdf')) and (files.`uid` =
users.`id`)
* There are many more advanced ways
@beckythebest

38. Use the Combos in Code
Now to get all Sarah’s PDFS is a short, clear statement:
val sarahsPdfs = db withSession {
implicit session =>
Users.userPDFS(“sarah@eatingwell.com”).list
}
sarahsPDFS is now a List of File case classes OR
continue to build on it further
@beckythebest

39. Slick Drawbacks
Not a lot of documentation for advanced use
Re-using Slicks collection methods for query building can
be confusing
Learning curve (compared to already knowing SQL) (If
you do)
Not the most efficient SQL
@beckythebest

40. Save Yourselves!
There is now code generation in Slick!
You don’t have to write out 65 Table class definitions like I did
@beckythebest

41. Summary
Slick uses Scala’s best features to bring type safety and
composability to your Relational Database access
• Static Typing
• Collection Methods
• For-Comprehensions
• Compositionality
@beckythebest

42. Resources
Slick Documentation: http://slick.typesafe.com/doc/2.1.0/
Activator’s Hello Slick! http://typesafe.com/activator/template/hello-slick
Adam Mackler’s Learning Slick V2
https://mackler.org/LearningSlick2/
IRC chat room #scala on Freenode
Advanced Query Composing:
http://slick.typesafe.com/talks/2013-12-03_Scala-eXchange/
2013-12-03_Patterns-for-Slick-database-applications-
Scala-eXchange.pdf
Working around the 22 tuple limit:
http://stackoverflow.com/questions/20555304/how-can-i-use-the-
new-slick-2-0-hlist-to-overcome-22-column-limit
@beckythebest

43. Thank You
Questions?
Rebecca Grenier
rebeccagrenier@gmail.com
@beckythebest
Special Thanks to: Underscore Consulting
@beckythebest