Error when trying to filter by UUID - Slick

Question

I'm trying to filter my table with:

val applicationId = ...
val application = Applications.filter(_.id === applicationId).first

where id and applicationId are UUIDs.

I was getting an error that:

scala.slick.SlickException: UUID does not support a literal representation

I found that I need to use bind:

// val applicationId is a UUID
val application = Applications.filter(_.id === applicationId.bind).first

However, this is throwing an exception

java.util.NoSuchElementException: Invoker.first

even though I am querying with a UUID that I know is in the table

This is the selectStatement that Slick is producing. I'm not sure why it doesn't include the UUID?

select x2."Id" from "Application" x2 where x2."Id" = ?

Answer 1

I've been struggling with this today. I don't know if I have a good solution, but I can give a few options.

Patch slick driver to allow equality test

I'm using MySQL and that database supports a syntax to send byte data as a string:

mysql> desc user;
+---------------+--------------+------+-----+---------+-------+
| Field         | Type         | Null | Key | Default | Extra |
+---------------+--------------+------+-----+---------+-------+
| user_uuid     | binary(16)   | NO   | PRI | NULL    |       |
| email         | varchar(254) | NO   | UNI | NULL    |       |
| display_name  | varchar(254) | NO   |     | NULL    |       |
| password_hash | varchar(254) | YES  |     | NULL    |       |
+---------------+--------------+------+-----+---------+-------+
4 rows in set (0.01 sec)

mysql> select * from user where user_uuid = x'e4d369040f044b6e9561765c356907d3';
+------------------+-----------------+--------------+---------------+
| user_uuid        | email           | display_name | password_hash |
+------------------+-----------------+--------------+---------------+
| ????????????     | foo@example.com | Foo          | NULL          |
+------------------+-----------------+--------------+---------------+
1 row in set (0.00 sec)

To show that the UUID is correct:

mysql> select hex(user_uuid), email, display_name from user where user_uuid = x'e4d369040f044b6e9561765c356907d3';
+----------------------------------+-----------------+--------------+
| hex(user_uuid)                   | email           | display_name |
+----------------------------------+-----------------+--------------+
| E4D369040F044B6E9561765C356907D3 | foo@example.com | Foo          |
+----------------------------------+-----------------+--------------+

On that basis, the following patch to MySQLDriver.scala (version 1.0.1) works nicely:

$ git diff
diff --git a/src/main/scala/scala/slick/driver/MySQLDriver.scala b/src/main/scala/scala/slick/driver/
index 84a667e..1aa5cca 100644
--- a/src/main/scala/scala/slick/driver/MySQLDriver.scala
+++ b/src/main/scala/scala/slick/driver/MySQLDriver.scala
@@ -174,9 +174,15 @@ trait MySQLDriver extends ExtendedDriver { driver =>
       }
     }

+    import java.util.UUID
+
     override val uuidTypeMapperDelegate = new UUIDTypeMapperDelegate {
       override def sqlType = java.sql.Types.BINARY
       override def sqlTypeName = "BINARY(16)"
+
+    override def valueToSQLLiteral(value: UUID): String =
+      "x'"+value.toString.replace("-", "")+"'"
     }
   }
 }

With that you can do code like:

def findUserByUuid(uuid: UUID): Option[UserRecord] = db.withSession {
  // Note: for this to work with slick 1.0.1 requires a tweak to MySQLDriver.scala
  // If you don't, the "===" in the next line will fail with:
  // "UUID does not support a literal representation".
  val query = (for (u <- UserRecordTable if u.uuid === uuid) yield u)
  query.firstOption
}

I'm not sure which database you're using but a similar approach may work. I haven't performance tested any of this.

Encode the UUID as byte array

There are a few options to avoid the slick code patch.

Using the UUIDHelper from http://nineofclouds.blogspot.com.au/2013/04/storing-uuids-with-anorm.html, you can encode the UUID into a byte array and do a static query. Somewhat inelegant but works like:

import UuidHelper

implicit object SetUUID extends SetParameter[UUID] {
  def apply(v: UUID, pp: PositionedParameters) { pp.setBytes(UuidHelper.toByteArray(v)) }
}
implicit val getUserRecordResult = GetResult(r => 
  UserRecord(UuidHelper.fromByteArray(r.nextBytes()), r.<<, r.<<, r.<<)
)

val userByUuid = StaticQuery[UUID, UserRecord] + "select * from user where user_uuid = ?"
val user = userByUuid(user.uuid).first
// do what you want with user.

Encode UUID as hex string

The below is probably the least elegant, but included for completeness:

implicit val getUserRecordResult = GetResult(r => UserRecord(UuidHelper.fromByteArray(r.nextBytes()), r.<<, r.<<, r.<<))

val uuid = user.uuid.toString.replace("-", "")
val userByUuid = StaticQuery.queryNA[UserRecord](s"select * from user where user_uuid = x'$uuid'")
val user = userByUuid().first

HTH

EDIT: a pull request against master below. Note that the pull request is against master (2.0.0), but I tested it successfully only against 1.0.1.

https://github.com/slick/slick/pull/240