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Exposed Overview Kotlin

Exposed is a lightweight SQL library written in Kotlin, which provides a DSL (Domain Specific Language) for querying and manipulating SQL databases. It aims to simplify database interactions by providing a type-safe and fluent API.

In this tutorial, we will explore the history, features, and examples of Exposed Kotlin Framework.

History​

Exposed was created by JetBrains as an alternative to existing ORM (Object-Relational Mapping) libraries for Kotlin. It was designed to be simple, lightweight, and easy to use, while still providing powerful database manipulation capabilities.

Feature​

  1. Type-safe DSL: Exposed provides a type-safe DSL for building SQL queries. This ensures that queries are checked at compile-time, reducing the chance of runtime errors.

    val query = Users.select { Users.id eq 1 }

  2. Fluent API: The API provided by Exposed is fluent and expressive, allowing for easy construction of complex queries.

    val query = Users.select { (Users.id eq 1) and (Users.name like "%John%") }

  3. Schema Definition: Exposed allows you to define database schemas using Kotlin code. This eliminates the need for separate SQL scripts and provides better type-safety.

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

  4. Transactions: Exposed supports transaction management, allowing you to group multiple database operations into a single transaction.

    transaction {
        Users.insert { it[name] = "John" }
        Users.insert { it[name] = "Jane" }
    }

  5. Querying: Exposed provides various methods for querying the database, including filtering, sorting, and joining.

    val query = Users.select { Users.age greaterEq 18 }.orderBy(Users.name)

  6. Updating and Deleting: Exposed allows you to update and delete records in the database using a simple syntax.

    Users.update({ Users.id eq 1 }) {
        it[name] = "John Doe"
    }

    Users.deleteWhere { Users.age less 18 }

  7. Database Support: Exposed supports multiple database backends, including SQLite, MySQL, PostgreSQL, and H2.

Examples of Exposed Kotlin Framework​

Example 1: Creating a User Table​

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

Example 2: Inserting Records​

transaction {
    Users.insert {
        it[name] = "John"
        it[age] = 25
    }

    Users.insert {
        it[name] = "Jane"
        it[age] = 30
    }
}

Example 3: Querying Records​

val query = Users.select { Users.age greaterEq 18 }.orderBy(Users.name)

for (row in query) {
    val name = row[Users.name]
    val age = row[Users.age]
    println("$name, $age")
}

Example 4: Updating Records​

Users.update({ Users.id eq 1 }) {
    it[name] = "John Doe"
}

Example 5: Deleting Records​

Users.deleteWhere { Users.age less 18 }

For more information, you can visit the official Exposed website: https://github.com/JetBrains/Exposed

Exposed Kotlin Framework provides a powerful and intuitive way to interact with SQL databases in Kotlin. Its type-safe DSL, fluent API, and support for various database backends make it a great choice for Kotlin developers.