trjhtr

I implemented a simple Java JDBC wrapper in Kotlin with Arrow functional library.

/**
 * Executes simple SQL statement that takes no arguments.
 * E.g. "CREATE TABLE" statement.
 *
 * @return IO with either an exception or boolean result
 */
fun String.executeStatement(dataSource: DataSource): IO<Either<Throwable, Boolean>> 
 val connection = dataSource.connection
 return IO connection.createStatement().execute(this) .attemptAndCloseConnection(connection)


/**
 * Executes prepared SQL statement (a statement that takes arguments).
 * E.g. "INSERT, UPDATE, DELETE..." statements.
 *
 * @return IO with either an exception or with result of execution as an integer
 */
fun String.executePreparedStatement(dataSource: DataSource, vararg args: Any): IO<Either<Throwable, Int>> 
 val connection = dataSource.connection
 return IO 
 val preparedStatement = connection.prepareStatement(this)
 args.forEachIndexed() idx, arg -> preparedStatement.setObject(idx + 1, arg) 
 preparedStatement.executeUpdate()
 .attemptAndCloseConnection(connection)


/**
 * Executes SQL query
 */
fun <E> String.executeQuery(dataSource: DataSource, resultSetMapper: (ResultSet) -> E, vararg args: Any): IO<Either<Throwable, List<E>>> 
 val connection = dataSource.connection
 return IO 
 val list = mutableListOf<E>()
 val preparedStatement = connection.prepareStatement(this)
 args.forEachIndexed() idx, arg -> preparedStatement.setObject(idx + 1, arg) 
 val resultSet = preparedStatement.executeQuery()
 while (resultSet.next()) 
 list.add(resultSetMapper(resultSet))
 
 list.toList()
 .attemptAndCloseConnection(connection)


private fun <A> IO<A>.attemptAndCloseConnection(connection: Connection?) =
 this.attempt().map connection?.close(); it 

Every result of execution is wrapped in an instance of IO to represent side-effects.

Functions are invoked directly on strings which produces an instance of Either<Throwable, T> when run:

val dataSource = HikariDataSource()
// add config for data source...

"""CREATE TABLE cities (
 id INTEGER PRIMARY KEY AUTO_INCREMENT,
 name VARCHAR(255) NOT NULL);""".executeStatement(dataSource)
 .unsafeRunSync()

"INSERT INTO cities (name) VALUES (?)".executePreparedStatement(dataSource, "New York").unsafeRunSync()

My major concerns are:

• Passing an instance of DataSource upon invocation of every function. E.g. with Scala, I could pass data source implicitly which would declutter invocations.


• Mutable list in executeQuery function. Is it even ok?


• Closing connection (attemptAndCloseConnection function) - is there some better way to do this?


• Other proposals?