exposed-wiki/DAO.md

• Overview
• Basic CRUD operations
  • Create
  • Read
  • Update
  • Delete

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Overview

The DAO (Data Access Object) API of Exposed, is similar to ORM frameworks like Hibernate with specific Kotlin API.
A DB table is represented by an object inherited from org.jetbrains.exposed.sql.Table like that:

object StarWarsFilms : Table() {
  val id: Column<Int> = integer("id").autoIncrement().primaryKey()
  val sequelId: Column<Int> = integer("sequel_id").uniqueIndex()
  val name: Column<String> = varchar("name", 50)
  val director: Column<String> = varchar("director", 50)
}

Tables that contains Int id with the name id can be declared like that:

object StarWarsFilms : IntIdTable() {
  val sequelId: Column<Int> = integer("sequel_id").uniqueIndex()
  val name: Column<String> = varchar("name", 50)
  val director: Column<String> = varchar("director", 50)
}

An entity instance or a row in the table is defined as a class instance:

class StarWarsFilm(id: EntityID<Int>) : IntEntity(id) {
 companion object : IntEntityClass<StarWarsFilm>(StarWarsFilms)

 var sequelId by StarWarsFilms.sequelId 
 var name     by StarWarsFilms.name
 var director by StarWarsFilms.director
}

Basic CRUD operations

Create

val movie = StarWarsFilm.new {
  name = "The Last Jedi"
  sequelId = 8
  director = "Rian Johnson"
}

Read

To get entities use one of the following

val movies = StarWarsFilm.all()
val movies = StarWarsFilm.find {StarWarsFilms.sequelId eq 8}
val movie = StarWarsFilm.findById(5)

• For a list of avaialable predicates see DSL Where expression.

Read a value from a property similarly to any property in a Kotlin class:

val name = movie.name

Update

Update a value of a property similarly to any property in a Kotlin class:

movie.name = "Episode VIII – The Last Jedi"

Delete

movie.delete()