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sqlest-extractors

sqlest-extractors is a small library for extracting case classes from table data:

  • Minimal work to set up sqlest-extractors with a new table type
  • Extractors are defined declaratively and are easily composed
  • Support for:
    • Tuples
    • Options
    • List, Seq, Map, etc.
    • Mapped values
    • Grouping rows into single results

Using sqlest-extractors

To use sqlest-extractors 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-extractors
  "Sonatype OSS Snapshots" at "http://oss.sonatype.org/content/repositories/snapshots/"
)

and the following library dependency

libraryDependencies ++= Seq(
  "uk.co.jhc" %% "sqlest-extractors" % "0.7.3"
)

sqlest-extractors is available for Scala 2.11

Overview

Table data consists of multiple Rows of cells.

To use sqlest-extractors:

  1. Determine the Row type
  2. Extend the CellExtractor trait to read a value from a cell in a Row
  3. Mixin ExtractorSyntax[Row]

Example - CSV

object CSVDefinitions {
  // Start with some type aliases for CSV data
  type CSVRow = List[String]
  type CSV = List[CSVRow]

  // Now define a simple parser
  def parse(input: String): CSV =
    input.split(scala.util.Properties.lineSeparator).toList.map(_.split(",").toList)

  // Sample contents of a csv file containing person information
  val csvFile = """
    |Anne,35,1,Old Kent Road,
    |Bob,45,2,Whitechapel,
    |Charlie,20,,Lost,
    """.trim.stripMargin

  // Parse it into our CSV type
  val parsedCsv: CSV = parse(csvFile)
}
import CSVDefinitions._
import sqlest.extractor.{ CellExtractor, ExtractorSyntax }

Implement the CellExtractor trait for CSVRow that will read a String

case class StringExtractor(index: Int) extends CellExtractor[CSVRow, String] {
  def read(row: CSVRow): Option[String] = {
    val cellValue = row(index)
    if (cellValue.trim.nonEmpty) Some(cellValue)
    else None
  }
}

Implement the CellExtractor trait for CSVRow that will read a Int

case class IntExtractor(index: Int) extends CellExtractor[CSVRow, Int] {
  def read(row: CSVRow): Option[Int] = scala.util.Try(Integer.parseInt(row(index))).toOption
}

Extend the application with ExtractorSyntax for the row type. This provides the methods extract, extractTuple and extractConstant.

object CSVApp extends ExtractorSyntax[CSVRow] {
  // Create some cell extractors
  val nameExtractor = StringExtractor(0)
  val ageExtractor = IntExtractor(1)
  val houseExtractor = IntExtractor(2)
  val streetExtractor = StringExtractor(3)

  // Create a tuple extractor that will read all fields
  val tupleExtractor =
    extractTuple(
      nameExtractor,
      ageExtractor,
      houseExtractor.asOption,
      streetExtractor.asOption)

  // Define the domain classes to extract from the CSV data
  case class Person(name: String, age: Int, address: Option[Address])
  case class Address(house: Int, street: String)

  // Create extractors to read the domain classes
  val addressExtractor = extract[Address](houseExtractor, streetExtractor)

  // Named arguments often enhance the readability of extractor definitions
  val personExtractor = extract[Person](
    name = nameExtractor,
    age = ageExtractor,
    address = addressExtractor.asOption)

  // `extractHeadOption` and `extractAll` must be passed an Iterable[CSVRow]
  // `List` implements `Iterable` so the parsedCsv can be used directly
  def tupleHeadOption = tupleExtractor.extractHeadOption(parsedCsv)
  def tupleAll = tupleExtractor.extractAll(parsedCsv)
  def addressHeadOption = addressExtractor.extractHeadOption(parsedCsv)
  def personAll = personExtractor.extractAll(parsedCsv)
}

extractHeadOption tries to read the first row. If there isn't one it returns None

scala> CSVApp.tupleHeadOption
res0: Option[(String, Int, Option[Int], Option[String])] = Some((Anne,35,Some(1),Some(Old Kent Road)))

scala> CSVApp.addressHeadOption
res1: Option[CSVApp.Address] = Some(Address(1,Old Kent Road))

extractAll reads all rows into a List

scala> CSVApp.tupleAll
res2: List[(String, Int, Option[Int], Option[String])] = List((Anne,35,Some(1),Some(Old Kent Road)), (Bob,45,Some(2),Some(Whitechapel)), (Charlie,20,None,Some(Lost)))

scala> CSVApp.personAll
res3: List[CSVApp.Person] = List(Person(Anne,35,Some(Address(1,Old Kent Road))), Person(Bob,45,Some(Address(2,Whitechapel))), Person(Charlie,20,None))

More examples

See the tests for more examples of:

  • ConstantExtractor
  • OptionExtractor
  • TupleExtractor
  • MappedExtractor
  • SeqExtractor
  • ListMultiRowExtractor
  • GroupedExtractor

Suggested usages

  • CSVs
  • java.util.ResultSet - this is what sqlest uses extractors for
  • Fixed format record data
  • Converting a list of Tuples into case classes