Schema Code Generation

The Slick code generator is a convenient tool for working with an existing or evolving database schema. It can be run stand-alone or integrated into your sbt build for creating all code Slick needs to work.

Overview

By default, the code generator generates Table classes, corresponding TableQuery values, which can be used in a collection-like manner, as well as case classes for holding complete rows of values. Since Slick 3.3 this is even true for tables with more than 22 columns. In order to accomplish the support of case classes with such a huge parameter count, despite Scala’s tuple size limit, some of the generated functions (like def * and def ?) use HLists internally and thus look somewhat different but behave the same as those for tables with less columns.

Parts of the generator are also explained in our talk at Scala eXchange 2013.

Standalone use

To include Slick’s code generator use the published library. For sbt projects add following to your build definition - build.sbt or project/Build.scala:

libraryDependencies += "com.typesafe.slick" %% "slick-codegen" % "3.5.1"

For Maven projects add the following to your <dependencies>:

<dependency>
  <groupId>com.typesafe.slick</groupId>
  <artifactId>slick-codegen_2.13</artifactId>
  <version>3.5.1</version>
</dependency>

copysourceimport scala.concurrent.ExecutionContext.Implicits.global
import scala.util.{Failure, Success}

import slick.jdbc.H2Profile
import slick.jdbc.H2Profile.api.*

Slick’s code generator comes with a default runner that can be used from the command line or from Java/Scala. You can simply execute

copysourceslick.codegen.SourceCodeGenerator.main(
  Array(uri, outputFolder)
)

or

copysourceslick.codegen.SourceCodeGenerator.main(
  Array(profile, jdbcDriver, url, outputFolder, pkg)
)

or

copysourceslick.codegen.SourceCodeGenerator.main(
  Array(profile, jdbcDriver, url, outputFolder, pkg, user, password)
)

and provide the following values

• uri: Config URL and/or fragment for path in typesafe config, e.g. url#slick.db.default
• profile: Fully qualified name of the profile class, e.g. slick.jdbc.H2Profile
• jdbcDriver: Fully qualified name of the JDBC driver class, e.g. org.h2.Driver
• url: JDBC url, e.g. jdbc:postgresql://localhost/test
• outputFolder: Place where the package folder structure should be put
• pkg: Scala package the generated code should be places in
• user: database connection user name
• password: database connection password
• outputToMultipleFiles: Boolean indicating if the generated output should be one big file or one file per table. Default is false.

Integrated into sbt

The code generator can be run before every compilation or manually in sbt. An example project showing both can be found here.

Generated Code

By default, the code generator places a file Tables.scala in the given folder in a subfolder corresponding to the package. The file contains an object Tables from which the code can be imported for use right away. Make sure you use the same profile. The file also contains a trait Tables which can be used in the cake pattern.

If outputToMultipleFiles is set to true, the code generator will instead create a trait per table. Tables.scala then stacks all the generated tables. The advantage of this, is that you avoid a potentially huge file

Customization

The generator can be flexibly customized by overriding methods to programmatically generate any code based on the data model. This can be used for minor customizations as well as heavy, model driven code generation, e.g. for framework bindings in Play, other data-related, repetitive sections of applications, etc.

This example shows a customized code-generator and how to setup up a multi-project sbt build, which compiles and runs it before compiling the main sources.

The implementation of the code generator is structured into a small hierarchy of sub-generators responsible for different fragments of the complete output. The implementation of each sub-generator can be swapped out for a customized one by overriding the corresponding factory method. SourceCodeGenerator contains a factory method Table, which it uses to generate a sub-generator for each table. The sub-generator Table in turn contains sub-generators for Table classes, entity case classes, columns, key, indices, etc. Custom sub-generators can easily be added as well.

Within the sub-generators the relevant part of the Slick data model can be accessed to drive the code generation.

Please see the api documentation for info on all of the methods that can be overridden for customization.

Here is an example for customizing the generator. Noteworthy, the line override def hugeClassEnabled = false disables generation of case classes for tables with more than 22 columns. A HList based type will be generated instead. So this way you get back the default behavior before the advent of Slick 3.3.

copysourceimport slick.codegen.SourceCodeGenerator
// fetch data model
val modelAction = H2Profile.createModel(Some(H2Profile.defaultTables)) // you can filter specific tables here
val modelFuture = db.run(modelAction)
// customize code generator
val codegenFuture = modelFuture.map(model => new SourceCodeGenerator(model) {
  // override mapped table and class name
  override def entityName =
    dbTableName => dbTableName.dropRight(1).toLowerCase.toCamelCase
  override def tableName =
    dbTableName => dbTableName.toLowerCase.toCamelCase

  // add some custom import
  override def code = "import foo.{MyCustomType,MyCustomTypeMapper}" + "\n" + super.code

  // override table generator
  override def Table = new Table(_){
    // disable entity class generation for tables with more than 22 columns
    override def hugeClassEnabled = false

    // override contained column generator
    override def Column = new Column(_){
      // use the data model member of this column to change the Scala type,
      // e.g. to a custom enum or anything else
      override def rawType =
        if(this.model.name == "SOME_SPECIAL_COLUMN_NAME") "MyCustomType" else super.rawType
    }
  }
})
codegenFuture.onComplete {
  case Success(codegen) =>
    codegen.writeToFile(
      "slick.jdbc.H2Profile","some/folder/","some.packag","Tables","Tables.scala"
    )
  case Failure(_) =>
}