Kotlin

sqltgen generates JDBC-based Kotlin code using the standard java.sql package. Generated code uses Kotlin idioms: data classes, nullable types, and Kotlin objects.

Configuration

"kotlin": {
  "out": "src/main/kotlin",
  "package": "com.example.db"
}

What is generated

src/main/kotlin/com/example/db/
  Author.kt         — data class for the author table
  Book.kt           — data class for the book table
  Queries.kt        — Kotlin object with query functions
  Querier.kt        — DataSource-backed wrapper object

Model data classes

// Author.kt
package com.example.db

data class Author(
    val id: Long,
    val name: String,
    val bio: String?,      // nullable → T?
    val birthYear: Int?    // nullable → T?
)

• Non-null columns use non-nullable Kotlin types (Long, Int, Boolean, etc.).
• Nullable columns use Kotlin nullable types (Long?, Int?, String?, etc.).
• snake_case SQL names → camelCase Kotlin property names.

Query functions

// Queries.kt
package com.example.db

import java.sql.Connection

object Queries {

    fun getAuthor(conn: Connection, id: Long): Author? { … }

    fun listAuthors(conn: Connection): List<Author> { … }

    fun createAuthor(conn: Connection, name: String, bio: String?,
                     birthYear: Int?): Author? { … }

    fun deleteAuthor(conn: Connection, id: Long): Unit { … }

    fun countAuthors(conn: Connection): Long { … }  // :execrows
}

Querier wrapper

// Querier.kt
package com.example.db

import javax.sql.DataSource

class Querier(private val ds: DataSource) {

    fun getAuthor(id: Long): Author? =
        ds.connection.use { Queries.getAuthor(it, id) }

    fun listAuthors(): List<Author> =
        ds.connection.use { Queries.listAuthors(it) }
    // …
}

Wiring up

Gradle dependency

// build.gradle.kts — PostgreSQL driver
dependencies {
    implementation("org.postgresql:postgresql:42.7.3")
    // SQLite:
    // implementation("org.xerial:sqlite-jdbc:3.47.0.0")
    // MySQL:
    // implementation("com.mysql:mysql-connector-j:9.1.0")
}

Using a plain Connection

import java.sql.DriverManager
import com.example.db.Queries

val conn = DriverManager.getConnection(
    "jdbc:postgresql://localhost:5432/mydb", "user", "pass")

val author = Queries.getAuthor(conn, 1L)
val all    = Queries.listAuthors(conn)

Using the Querier wrapper

import com.zaxxer.hikari.HikariDataSource
import com.example.db.Querier

val ds = HikariDataSource().apply {
    jdbcUrl  = "jdbc:postgresql://localhost:5432/mydb"
    username = "user"
    password = "pass"
}

val q = Querier(ds)
val author = q.getAuthor(1L)

Inline row types

object Queries {

    data class ListBooksWithAuthorRow(
        val id: Long,
        val title: String,
        val genre: String,
        val price: java.math.BigDecimal,
        val authorName: String,
        val authorBio: String?
    )

    fun listBooksWithAuthor(conn: Connection): List<ListBooksWithAuthorRow> { … }
}

Naming conventions