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sqlest

sqlest is a database library for Scala. It allows you to write SQL directly in Scala with type safety guarantees while also providing a simple mechanism of extracting domain specific case classes from the results.

sqlest-extractors is a second library used for extracting case classes from table data. It is used within sqlest. Check out the readme

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Using sqlest

To use sqlest from an existing project add the following resolvers

resolvers ++= Seq(
  "Sonatype OSS Releases"  at "http://oss.sonatype.org/content/repositories/releases/",
  // Only needed if you are using a snapshot version of sqlest
  "Sonatype OSS Snapshots" at "http://oss.sonatype.org/content/repositories/snapshots/"
)

and the following library dependency

libraryDependencies ++= Seq(
  "uk.co.jhc" %% "sqlest" % "0.8.6"
)

sqlest is available for Scala 2.11

Examples

Database Connection

Before doing anything else a connection to a database must be available. This is encapsulated in the Database object which requires a DataSource and a StatementBuilder.

import sqlest._

Configure a DataSource

val dataSource = {
  val dataSource = new org.h2.jdbcx.JdbcDataSource
  dataSource.setURL("jdbc:h2:~/test")
  dataSource
}

Choose the StatementBuilder that is compatible with the database you are using.

val statementBuilder = sqlest.sql.H2StatementBuilder

Use the DataSource and the StatementBuilder to create an implicit database. This database is used in all execute calls.

implicit val database = Database.withDataSource(dataSource, statementBuilder)

Table and column definitions

A table definition consists of a table name and any columns that you want to use. A table can be created with an alias but it is standard to create an object that has no alias.

class FruitTable(alias: Option[String]) extends Table("fruit", alias) {
  val id = column[Int]("id")
  val name = column[String]("name")
  val juiciness = column[Int]("juiciness")
}
object FruitTable extends FruitTable(None)

class SmoothyTable(alias: Option[String]) extends Table("smoothy", alias) {
  val id = column[Int]("id")
  val description = column[String]("description")
}
object SmoothyTable extends SmoothyTable(None)

class IngredientsTable(alias: Option[String]) extends Table("ingredients", alias) {
  val smoothyId = column[Int]("smoothy_id")
  val fruitId = column[Int]("fruit_id")
}
object IngredientsTable extends IngredientsTable(None)

Domain classes

Let's define some domain classes that we want to populate from our database

case class Fruit(name: String, juiciness: Int)
case class Smoothy(description: String, fruits: List[Fruit])

Extractors

Extractors are used to populate domain classes from ResultSets returned by running queries. They declaratively specify which parameter in a case class is populated by which column in a table

lazy val fruitExtractor = extract[Fruit](
  name = FruitTable.name,
  juiciness = FruitTable.juiciness
)

Querying

Queries are written in sqlest the same way as they are written in SQL. The table and column definitions are used directly. Here is a query that will return the juiciest fruits

scala> select(FruitTable.name, FruitTable.juiciness).
     |   from(FruitTable).
     |   where(FruitTable.juiciness >= 8).
     |   orderBy(FruitTable.juiciness.desc).
     |   extractAll(fruitExtractor)    // fruitExtractor is defined below
res11: List[fruitExtractor.SingleResult] = List(Fruit(Watermelon,10), Fruit(Tomato,9), Fruit(Grape,8))

Extractors are designed for composition to allow nested case classes to be extracted, and multiple rows of the ResultSet to be combined into a single result

lazy val smoothyExtractor = extract[Smoothy](
  description = SmoothyTable.description,
  fruits = fruitExtractor.asList
).groupBy(SmoothyTable.id) // All results with the same value for this field are combined into a single result

This extractor can then be used to find out which fruits are used in a smoothy

scala> select.
     |   from(SmoothyTable).
     |   innerJoin(IngredientsTable).on(SmoothyTable.id === IngredientsTable.smoothyId).
     |   innerJoin(FruitTable).on(IngredientsTable.fruitId === FruitTable.id).
     |   where(SmoothyTable.description === "Super banana smoothie").
     |   extractHead(smoothyExtractor)
res12: smoothyExtractor.SingleResult = Smoothy(Super banana smoothie,List(Fruit(Banana,4), Fruit(Grape,8)))

Authors

Contributors

Acknowledgements

  • Dean Chapman - author of Sqler which inspired sqlest
  • Frank Wallis - ideas, feedback and contributions
  • Slick - a great project which contains many ideas used in sqlest
  • jOOQ - a similar project written in Java which provided many ideas used in sqlest