JDBC ResultSet to Data Class

JdbcToDataClass.kt

// Bring in Google Guava as a dependency
// compile 'com.google.guava:guava:22.0'


import com.google.common.base.CaseFormat
import java.sql.ResultSet


fun ResultSet.toDataClass(): String {

    val table = metaData.getTableName(1).let { it.substring(0,1) + CaseFormat.UPPER_UNDERSCORE.to(CaseFormat.LOWER_CAMEL, it.substring(1)) }
    val headers = (1..metaData.columnCount).asSequence()
            .map { metaData.getColumnName(it) }
            .toList()

    val types = (1..metaData.columnCount).asSequence()
            .map {
                it to when  {
                    metaData.getColumnClassName(it).contains(".Integer") -> "Int"
                    metaData.getColumnClassName(it).contains(".String") -> "String"
                    metaData.getColumnClassName(it).contains(".Date") -> "LocalDate"
                    metaData.getColumnClassName(it).contains(".Timestamp") -> "LocalDateTime"
                    metaData.getColumnClassName(it).contains(".BigDecimal") -> "BigDecimal"
                    metaData.getColumnClassName(it).contains(".Long") -> "Long"
                    else -> "String"
                }
            }.map { if (metaData.isNullable(it.first) == 1) "${it.second}?" else it.second }
            .toList()

    fun buildField(index: Int) = "    val ${CaseFormat.UPPER_UNDERSCORE.to(CaseFormat.LOWER_CAMEL, headers[index])}: ${types[index]}"

    val parameters = headers.map { CaseFormat.UPPER_UNDERSCORE.to(CaseFormat.LOWER_CAMEL, it) }

    val tableFields = (0..(headers.size - 1)).asSequence().map { buildField(it) }.joinToString(",\n")

    data class TypeHeaderParameter(val type: String, val header: String, val parameter: String)
    val resultSetConstructor = types.asSequence().zip(headers.asSequence()).zip(parameters.asSequence())
            .map { TypeHeaderParameter(it.first.first, it.first.second, it.second) }
            .map { thp ->
                val header = "\"${thp.header}\""
                val parameter = "${thp.parameter} ="
                when(thp.type.replace("?","")) {
                    "Int" -> "$parameter rs.getInt($header)"
                    "String" -> "$parameter rs.getString($header)"
                    "LocalDate" -> "$parameter rs.getLocalDate($header)"
                    "LocalDateTime" -> "$parameter rs.getLocalDateTime($header)"
                    "BigDecimal" -> "$parameter rs.getBigDecimal($header)"
                    "Long" -> "$parameter rs.getLong($header)"
                    else -> throw Exception("Unmapped type!")
                }
            }.joinToString(",\n    ").let { "constructor(rs: ResultSet): this(\n    $it\n)"}

    return "data class $table (\n$tableFields\n) {\n $resultSetConstructor \n}"
}


fun ResultSet.getLocalDate(colName: String) = this.getDate(colName)?.toLocalDate()
fun ResultSet.getLocalDate(colIndex: Int) = this.getDate(colIndex)?.toLocalDate()

fun ResultSet.getLocalDateTime(colName: String) = this.getTimestamp(colName)?.toLocalDateTime()
fun ResultSet.getLocalDateTime(colIndex: Int) = this.getTimestamp(colIndex)?.toLocalDateTime()