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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?