/kotlin-exposed-patterns

name: kotlin-exposed-patterns
description: JetBrains Exposed ORM patterns including DSL queries, DAO pattern, transactions, HikariCP connection pooling, Flyway migrations, and repository pattern.
metadata:
  origin: ECC

Kotlin Exposed Patterns

Comprehensive patterns for database access with JetBrains Exposed ORM, including DSL queries, DAO, transactions, and production-ready configuration.

When to Use

• Setting up database access with Exposed
• Writing SQL queries using Exposed DSL or DAO
• Configuring connection pooling with HikariCP
• Creating database migrations with Flyway
• Implementing the repository pattern with Exposed
• Handling JSON columns and complex queries

How It Works

Exposed provides two query styles: DSL for direct SQL-like expressions and DAO for entity lifecycle management. HikariCP manages a pool of reusable database connections configured via `HikariConfig`. Flyway runs versioned SQL migration scripts at startup to keep the schema in sync. All database operations run inside `newSuspendedTransaction` blocks for coroutine safety and atomicity. The repository pattern wraps Exposed queries behind an interface so business logic stays decoupled from the data layer and tests can use an in-memory H2 database.

Examples

DSL Query

suspend fun findUserById(id: UUID): UserRow? =
    newSuspendedTransaction {
        UsersTable.selectAll()
            .where { UsersTable.id eq id }
            .map { it.toUser() }
            .singleOrNull()
    }

DAO Entity Usage

suspend fun createUser(request: CreateUserRequest): User =
    newSuspendedTransaction {
        UserEntity.new {
            name = request.name
            email = request.email
            role = request.role
        }.toModel()
    }

HikariCP Configuration

val hikariConfig = HikariConfig().apply {
    driverClassName = config.driver
    jdbcUrl = config.url
    username = config.username
    password = config.password
    maximumPoolSize = config.maxPoolSize
    isAutoCommit = false
    transactionIsolation = "TRANSACTION_READ_COMMITTED"
    validate()
}

Database Setup

HikariCP Connection Pooling

// DatabaseFactory.kt
object DatabaseFactory {
    fun create(config: DatabaseConfig): Database {
        val hikariConfig = HikariConfig().apply {
            driverClassName = config.driver
            jdbcUrl = config.url
            username = config.username
            password = config.password
            maximumPoolSize = config.maxPoolSize
            isAutoCommit = false
            transactionIsolation = "TRANSACTION_READ_COMMITTED"
            validate()
        }

        return Database.connect(HikariDataSource(hikariConfig))
    }
}

data class DatabaseConfig(
    val url: String,
    val driver: String = "org.postgresql.Driver",
    val username: String = "",
    val password: String = "",
    val maxPoolSize: Int = 10,
)

Flyway Migrations

// FlywayMigration.kt
fun runMigrations(config: DatabaseConfig) {
    Flyway.configure()
        .dataSource(config.url, config.username, config.password)
        .locations("classpath:db/migration")
        .baselineOnMigrate(true)
        .load()
        .migrate()
}

// Application startup
fun Application.module() {
    val config = DatabaseConfig(
        url = environment.config.property("database.url").getString(),
        username = environment.config.property("database.username").getString(),
        password = environment.config.property("database.password").getString(),
    )
    runMigrations(config)
    val database = DatabaseFactory.create(config)
    // ...
}

Migration Files

-- src/main/resources/db/migration/V1__create_users.sql
CREATE TABLE users (
    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    name VARCHAR(100) NOT NULL,
    email VARCHAR(255) NOT NULL UNIQUE,
    role VARCHAR(20) NOT NULL DEFAULT 'USER',
    metadata JSONB,
    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
);

CREATE INDEX idx_users_email ON users(email);
CREATE INDEX idx_users_role ON users(role);

Table Definitions

DSL Style Tables

// tables/UsersTable.kt
object UsersTable : UUIDTable("users") {
    val name = varchar("name", 100)
    val email = varchar("email", 255).uniqueIndex()
    val role = enumerationByName<Role>("role", 20)
    val metadata = jsonb<UserMetadata>("metadata", Json.Default).nullable()
    val createdAt = timestampWithTimeZone("created_at").defaultExpression(CurrentTimestampWithTimeZone)
    val updatedAt = timestampWithTimeZone("updated_at").defaultExpression(CurrentTimestampWithTimeZone)
}

object OrdersTable : UUIDTable("orders") {
    val userId = uuid("user_id").references(UsersTable.id)
    val status = enumerationByName<OrderStatus>("status", 20)
    val totalAmount = long("total_amount")
    val currency = varchar("currency", 3)
    val createdAt = timestampWithTimeZone("created_at").defaultExpression(CurrentTimestampWithTimeZone)
}

object OrderItemsTable : UUIDTable("order_items") {
    val orderId = uuid("order_id").references(OrdersTable.id, onDelete = ReferenceOption.CASCADE)
    val productId = uuid("product_id")
    val quantity = integer("quantity")
    val unitPrice = long("unit_price")
}

Composite Tables

object UserRolesTable : Table("user_roles") {
    val userId = uuid("user_id").references(UsersTable.id, onDelete = ReferenceOption.CASCADE)
    val roleId = uuid("role_id").references(RolesTable.id, onDelete = ReferenceOption.CASCADE)
    override val primaryKey = PrimaryKey(userId, roleId)
}

DSL Queries

Basic CRUD

// Insert
suspend fun insertUser(name: String, email: String, role: Role): UUID =
    newSuspendedTransaction {
        UsersTable.insertAndGetId {
            it[UsersTable.name] = name
            it[UsersTable.email] = email
            it[UsersTable.role] = role