CRUD

Learn CRUD with insert, select, update and delete.

CRUD operations

CRUD stands for Create, Read, Update, Delete, the four basic database operations. Exposed has a function for each.

Create: Users.insert { it[name] = "Ayşe" }. Read: Users.select { Users.id eq 1 }. Update: Users.update { Users.name eq "Ayşe" where Users.id eq 1 }. Delete: Users.deleteWhere { Users.id eq 1 }. All calls live inside a transaction. Exposed generates SQL behind the scenes; you only work with the Kotlin API.

Exercise Call Users.insert

Define object Users : Table() with val id = integer("id") and val name = varchar("name", 50). In main, open a connection with Database.connect, then in a transaction block call Users.insert { it[name] = "Alex" } and print println("Record added").

Show example solution

object Users : Table() {
    val id = integer("id")
    val name = varchar("name", 50)
}

fun main() {
    Database.connect("jdbc:h2:mem:test", driver = "org.h2.Driver")
    transaction {
        Users.insert {
            it[name] = "Alex"
        }
        println("Record added")
    }
}

select, update, deleteWhere

select reads records: Users.select { Users.id eq 1 }. update modifies records: Users.update({ Users.id eq 1 }) { it[name] = "Ayşe" }.

deleteWhere removes records: Users.deleteWhere { Users.id eq 1 }. All queries use operators like eq, lessEq, greater for conditions. select returns a Query; you can iterate rows with .forEach { row -> ... }, get the first with .first(), or collect to a list with .toList().

Test yourself

Which function adds a new record?
- select
- insert
- deleteWhere
- update
Show answer

insert — insert adds a new record.

Complete the deleteWhere call

Users.____ { Users.id eq 1 }

Show answer

Users.deleteWhere { Users.id eq 1 }

Match CRUD operations

insert

Create
select

Read
update

Update
deleteWhere

Delete

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