Extension functions on JDBC Connection and ResultSet

LICENSE

Copyright 2016 Cameron Jordan

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

sql.kt

import java.math.BigDecimal
import java.sql.Connection
import java.sql.PreparedStatement
import java.sql.ResultSet
import java.sql.Timestamp
import java.time.Instant
import java.util.*

class PreparedStatementParameters(private val stmt: PreparedStatement) {
    private var index = 0

    fun param(value: Boolean) {
        index++
        stmt.setBoolean(index, value)
    }

    fun param(value: Byte) {
        index++
        stmt.setByte(index, value)
    }

    fun param(value: Short) {
        index++
        stmt.setShort(index, value)
    }

    fun param(value: Int) {
        index++
        stmt.setInt(index, value)
    }

    fun param(value: Long) {
        index++
        stmt.setLong(index, value)
    }

    fun param(value: Float) {
        index++
        stmt.setFloat(index, value)
    }

    fun param(value: Double) {
        index++
        stmt.setDouble(index, value)
    }

    fun param(value: BigDecimal) {
        index++
        stmt.setBigDecimal(index, value)
    }

    fun param(value: Instant) {
        index++
        stmt.setTimestamp(index, Timestamp.from(value))
    }

    fun param(value: Instant, calendar: Calendar) {
        index++
        stmt.setTimestamp(index, Timestamp.from(value), calendar)
    }

    fun param(value: String) {
        index++
        stmt.setString(index, value)
    }

    fun param(value: ByteArray) {
        index++
        stmt.setBytes(index, value)
    }

    fun param(value: IntArray) {
        index++
        val tmp = kotlin.arrayOfNulls<Int?>(value.count())

        // so, many, boxes, :(
        for (i in value.indices)
            tmp[i] = value[i]

        val sqlArray = stmt.connection.createArrayOf(SQL_TYPE_INT, tmp)
        stmt.setArray(index, sqlArray)
    }

    fun param(value: Array<String>) {
        index++
        val sqlArray = stmt.connection.createArrayOf(SQL_TYPE_STRING, value)
        stmt.setArray(index, sqlArray)
    }

    companion object {
        var SQL_TYPE_STRING = "text"
        var SQL_TYPE_INT = "int4"
    }
}

fun <T> Connection.execute(sql: String, params: PreparedStatementParameters.() -> Unit, block: (ResultSet) -> T): T {
    val stmt = this.prepareStatement(sql)
    try {
        PreparedStatementParameters(stmt).params()
        val rs = stmt.executeQuery()
        try {
            return block(rs)
        }
        finally {
            rs.close()
        }
    } finally {
        stmt.close()
    }
}

fun Connection.execute(sql: String, params: PreparedStatementParameters.() -> Unit) {
    val stmt = this.prepareStatement(sql)
    try {
        PreparedStatementParameters(stmt).params()
        stmt.execute()
    } finally {
        stmt.close()
    }
}

class ResultSetIterator<out T>(private val resultSet: ResultSet, private val selector: (ResultSet) -> T) : Iterator<T> {
    override fun hasNext() = resultSet.next()
    override fun next() = selector(resultSet)
}

fun <T> ResultSet.asSequence(selector: (ResultSet) -> T) = ResultSetIterator(this, selector).asSequence()
fun ResultSet.asSequence() = ResultSetIterator(this, { it }).asSequence()

usage.kt

fun demo() {
    conn.execute("SELECT stuff, things FROM my_sproc(?, ?)", { param(someInt); param(someString) }) { resultSet ->
        val rows = resultSet.asSequence { SomeDataClass(it.getBytes(1), it.getDouble(2)) }
        for (row in rows) {
            // do something
        }
    }
}