1. Reactive Database Access in Scala with Slick 3
Ihor Mielientiev
AUGUST 3, 2015

2. AGENDA What is Slick? 1 Introduction To Slick 2 Reactive Slick 3 3
Reactive Streams in Slick 3 4
Advices 5
Pros & Cons (Summary) 6
Q&A 7

3. WHAT IS SLICK?
Slick is database query and access library for Scala
Slick IS NOT ORM it's Functional-Relational Mapper
Brings relational model to Scala (not hidden)
Natural fit (no impedance mismatch)
Stateless

4. Minimal Configuration

5. /resource/application.conf

6. Mapping

7. Slick Mapping

8. No XML, no Annotations, no “magic”
Slick Mapping
Do mapping in Scala
Type Safe
No XML, no Annotations, no “magic”

9. Scala collection-like API

10. Slick Querying
Get users with age > 20 OR

11. Slick Querying
Slick Generate Next SQL (H2):

12. Slick Querying (Insert)
Inserting
Batching
Insert or update

13. Slick Querying (Insert 2)
Insert and return object
Batching with returning object

14. Slick Querying (Update / Delete)
A query for an UPDATE statement must resolve to a comprehension with a single table
Delete
A query for deleting must only select from a single table.

15. Joins
Cross Join
Inner Join

16. Joins
Left Join
Right Join
Full Join

17. Joins
It's too simple... Lets consider more complex example.
Get all users' addresses,
who subscribed on “New York Times“ and has age > 18 and lives in USA

18. Joins

19. Joins (for-comprehension)

20. Joins Generated SQL
Applicative join
Monadic join

21. Joins Generated SQL
If changes 'filter' order in
applicative joins...
Be careful, and look
at generated SQL

22. Transactions
- Transactions disabled by default
- To enable transaction just add .transactionally

23. Transactions

24. Pre Compiled Queries

25. Plain SQL
- Slick allows you to write your own SQL
- Plain SQL queries in Slick are built via string interpolation
using the sql, sqlu and tsql
- sqlu is used for DML statements which produce a row count
instead of a result set.

26. Plain SQL
- sql is used for statements which produce a result set.
- For mapping sql result to Model, you need to implement GetResult

27. Type-checked SQL
- Ability to type check hand-written SQL statements
Add annotation:
Use it (tsql):

28. Type-checked SQL
Bad syntax:

29. Type-checked SQL
Incorrect type:

30. Type-checked SQL
Table doesn't exist:
Field name error:

31. - Compilation depends on running DB
Type-checked SQL (Issues)
- Compilation depends on running DB
- Increase compilation time
- Limited IDE support

32. Supported Databases
- DB2 (via slick-extensions)
- Derby/JavaDB
- H2
- HSQLDB/HyperSQL
- Microsoft SQL Server (via slick-extensions)
- MySQL
- Oracle (via slick-extensions)
- PostgreSQL
- SQLite

33. Reactive Slick 3

34. Reactive Streams In Slick 3
- Reactive Streams is an initiative to provide a standard for asynchronous stream
processing with non-blocking back pressure.
- Reactive Streams is a “protocol” for efficiently passing data between two
independent units of execution (producer & consumer) in an asynchronous, non-blocking and bounded fashion.

35. Advices
1. Always view on generated SQL
2. Try to get data you actually need in that moment (Query granularity)
3. Stay tuned with updates
4. Learn SQL

36. Pros Cons Summary - Generated SQL is far from perfect + Full Control
+ Type Safe
+ Composable Queries
+ Reactive
+ Minimal Boilerplate
- Generated SQL is far from perfect
- Not always intuitive
- DSL has limitations

37. Thank you
Questions?