Reactive Database Access With Slick 3

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

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AGENDA
What is Slick?1
Introduction To Slick2
Reactive Slick 33
Reactive Streams in Slick 34
Advices5
Pros & Cons (Summary)6
Q&A7

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• 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
WHAT IS SLICK?

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Minimal
Configuration

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/resource/application.conf

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Mapping

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Slick Mapping

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

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Scala collection-like API

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Slick Querying
Get users with age > 20
OR

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Slick Querying
Slick Generate Next SQL (H2):

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Slick Querying (Insert)
Inserting
Batching
Insert or update

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

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Slick Querying (Update / Delete)
Update
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.

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Joins
Cross Join
Inner Join

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Joins
Left Join
Right Join
Full Join

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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

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Joins

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Joins (for-comprehension)

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Joins Generated SQL
Applicative join Monadic join

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

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

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Transactions

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Pre Compiled Queries

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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.

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

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

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Type-checked SQL
Bad syntax:

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Type-checked SQL
Incorrect type:

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

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

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

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Reactive Slick 3

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Reactive Streams In Slick 3
- Reactive Streams is an initiative to provide a standard for asynchronous stream
processing with non-blocking back pressure.
http://www.reactive-streams.org/
- 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.

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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

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

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Thank you
Questions?