exposed-wiki/DSL.md

• Overview
• Basic CRUD operations
  • Create
  • Read
  • Update
  • Delete
• Where expression
• Count
• Order-by
• Group-by
• Limit
• Join
• Alias
• Batch Insert

---

Overview

The DSL (Domain Specific Language) API of Exposed, is similar to actual SQL statements with type safety that Kotlin offers.
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)
}

Basic CRUD operations

Create

val id = StarWarsFilms.insertAndGetId {
  it[name] = "The Last Jedi"
  it[sequelId] = 8
  it[director] = "Rian Johnson"
}

Read

val query: Query = StarWarsFilms.select { StarWarsFilms.sequelId eq 8 }

Query inherit Iterable so it is possible to traverse it with map/foreach etc'. For example:

StarWarsFilms.select { StarWarsFilms.sequelId eq 8 }.forEach {
  println(it[StarWarsFilms.name])
}

If you want to select only distinct value then use withDistinct() function:

val directors = StarWarsFilms.
   slice{ StarWarsFilms.director }.
   select { StarWarsFilms.sequelId < 5 }.
   withDistinct().map {
      it[StarWarsFilms.director]
   }

Update

StarWarsFilms.update ({ StarWarsFilms.sequelId eq 8 }) {
  it[name] = "Episode VIII – The Last Jedi"
}

If you want to update column value with some expression like increment:

StarWarsFilms.update({ StarWarsFilms.sequelId eq 8 }) {
    with(SqlExpressionBuilder) {
       it.update(StarWarsFilms.sequelId, StarWarsFilms.sequelId + 1)
    }
} 

Delete

StarWarsFilms.deleteWhere { StarWarsFilms.sequelId eq 8 }

Where expression

Query expression (where) expects a boolean operator (ie: Op<Boolean>).
Allowed conditions are:

eq - (==)
neq - (!=)
isNull()
isNotNull()
less - (<)
lessEq - (<=)
greater - (>)
greaterEq - (>=)
like - (=~)
notLike - (!~)
regexp
notRegexp
inList
notInList
between
match (MySQL MATCH AGAINST) 

Allowed logical conditions are:

and
or

Count

count() is a method of Query that is used like below example:

val count = StarWarsFilms.select { StarWarsFilms.sequelId eq  8 }.count()

Order-by

Order-by accepts a list of columns mapped to boolean indicates if sorting should be ascending or descending. Example:

StarWarsFilms.selectAll().orderBy(StarWarsFilms.sequelId to true)

Group-by

In group-by, define fields and their functions (such as count) by the slice() method.

StarWarsFilms
  .slice(StarWarsFilms.sequelId.count(), StarWarsFilms.director)
  .selectAll()
  .groupBy(StarWarsFilms.director)

Available functions are:

count
sum
max
min
average
...

Limit

You can use limit function to prevent loading large data sets or use it for pagination with second offset parameter.

// Take 2 films after the first one.
StarWarsFilms.select { StarWarsFilms.sequelId eq Players.sequelId }.limit(2, offset = 1)

Join

For join example consider the following tables:

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)
}

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

Join to count how many players play in each movie:

(Players innerJoin StarWarsFilms)
  .slice(Players.name.count(), StarWarsFilms.name)
  .select { StarWarsFilms.sequelId eq Players.sequelId }
  .groupBy(StarWarsFilms.name)

• In case there is a foreign key it is possible to replace select{} with selectAll()

Alias

Aliases allow preventing ambiguity between field names and table names. Use the aliased var instead of original one:

val filmTable1 = StarWarsFilms.alias("ft1")
filmTable1.selectAll() // can be used in joins etc'

Batch Insert

Batch Insert allow mapping a list of entities into DB raws in one sql statement. It is more efficient than inserting one by one as it initiates only one statement. Here is an example:

val cityNames = listOf("Paris", "Moscow", "Helsinki")
val allCitiesID = cities.batchInsert(cityNames) { name ->
  this[cities.name] = name
}