Custom LocalDateTime parser in Slick 3 - scala

Question

I'm converting a bunch of java.sql.Timestamp columns from my Slick 3 models into LocalDateTime. My database backend is MySQL 8 and the columns I'm converting are either TIMESTAMP or DATETIME.
I ran into issues with MySQL returning dates in format yyyy-MM-dd HH:mm:ss, while LocalDateTime.parse expects yyyy-MM-dd'T'HH:mm:ss. This results in runtime errors such as java.time.format.DateTimeParseException: Text '2022-12-05 08:01:08' could not be parsed at index 10.
It found that it could be solved by using a custom formatter, like this:
private val formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")
val localDateTimeMapper: BaseColumnType[LocalDateTime] = MappedJdbcType.base[LocalDateTime, String](
ldt => ldt.format(formatter),
s => LocalDateTime.parse(s, formatter)
)
Normally I would define the formatter as implicit, but it creates a compile error in the model: No implicits found for parameter tt: TypedType[LocalDateTime]. Applying the formatter explicitly works wonderful for column[LocalDateTime], but does not work for column[Option[LocalDateTime]] (causes Type mismatch, required TypedType[Option[LocalDateTime]]).
class Users(tag: Tag) extends Table[User](tag, "users") {
def uuid = column[UUID]("uuid", O.PrimaryKey)
def name = column[String]("name")
def email = column[String]("email")
def lastSignedInAt = column[Option[LocalDateTime]]("last_signed_in_at")(localDateTimeMapper)
def createdAt = column[LocalDateTime]("created_at")(localDateTimeMapper)
override def * = (uuid, name, email, lastSignedInAt, createdAt) <> (User.tupled, User.unapply)
}
Other custom types (such as enums) works without issues using the implicit formatter approach, but I suspect the issue here is that Slick has a LocalDateTime-mapper that I'm trying to override. From what I can tell Slick wants LocalDateTime objects to be stored as VARCHAR rather than date types, but I don't want to convert the database columns.
Any advise on how I can make my custom formatter work (or use built in functionality in Slick) to allow LocalDateTime to work with MySQL's date types?

Answer 1

I eventually found a way that works by extending Slick's MySQLProfile:
package lib
import slick.jdbc.JdbcProfile
import java.sql.PreparedStatement
import java.sql.ResultSet
import java.time.LocalDateTime
import java.time.format.DateTimeFormatter
trait ExMySQLProfile extends JdbcProfile with slick.jdbc.MySQLProfile { driver =>
private val localDateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")
override val columnTypes = new ExJdbcTypes
class ExJdbcTypes extends super.JdbcTypes {
#inline
private[this] def stringToMySqlString(value: String): String = {
value match {
case null => "NULL"
case _ =>
val sb = new StringBuilder
sb.append('\'')
for (c <- value) c match {
case '\'' => sb.append("\\'")
case '"' => sb.append("\\\"")
case 0 => sb.append("\\0")
case 26 => sb.append("\\Z")
case '\b' => sb.append("\\b")
case '\n' => sb.append("\\n")
case '\r' => sb.append("\\r")
case '\t' => sb.append("\\t")
case '\\' => sb.append("\\\\")
case _ => sb.append(c)
}
sb.append('\'')
sb.toString
}
}
/**
* Override LocalDateTime handler, to parse values as we expect them.
*
* The default implementation in Slick does not support TIMESTAMP or DATETIME
* columns, but expects timestamps to be stored as VARCHAR
*/
override val localDateTimeType: LocalDateTimeJdbcType = new LocalDateTimeJdbcType {
override def sqlType: Int = java.sql.Types.TIMESTAMP
override def setValue(v: LocalDateTime, p: PreparedStatement, idx: Int): Unit = {
p.setString(idx, if (v == null) null else v.toString)
}
override def getValue(r: ResultSet, idx: Int): LocalDateTime = {
r.getString(idx) match {
case null => null
case iso8601String => LocalDateTime.parse(iso8601String, localDateTimeFormatter)
}
}
override def updateValue(v: LocalDateTime, r: ResultSet, idx: Int) = {
r.updateString(idx, if (v == null) null else v.format(localDateTimeFormatter))
}
override def valueToSQLLiteral(value: LocalDateTime): String = {
stringToMySqlString(value.format(localDateTimeFormatter))
}
}
}
}
trait MySQLProfile extends ExMySQLProfile {}
object MySQLProfile extends MySQLProfile
In my application.conf I've configured the profile with:
slick.dbs.default {
profile = "lib.MySQLProfile$"
}