尝试按UUID过滤时出错 - Slick

Question

我正在尝试使用以下方法过滤我的表格：

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

在这里，id 和 applicationId 都是UUIDs。

我遇到了一个错误：

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

我发现我需要使用 bind ：

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

然而，这会抛出异常。

java.util.NoSuchElementException: Invoker.first

尽管我使用的UUID在表中存在，但我仍在查询。
这是Slick生成的selectStatement。我不确定它为什么不包括UUID？

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

- AlexBrand

Answer 1

我今天一直在苦恼这个问题。我不知道是否有好的解决方案，但我可以提供几个选项。

### 补丁Slick驱动程序以允许等式测试

我正在使用MySQL数据库，该数据库支持将字节数据作为字符串发送的语法：

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 |
+------------------+-----------------+--------------+---------------+
| ????????????     | [e-mail] | Foo          | NULL          |
+------------------+-----------------+--------------+---------------+
1 row in set (0.00 sec)

为了表明UUID是正确的：

mysql> select hex(user_uuid), email, display_name from user where user_uuid = x'e4d369040f044b6e9561765c356907d3';
+----------------------------------+-----------------+--------------+
| hex(user_uuid)                   | email           | display_name |
+----------------------------------+-----------------+--------------+
| E4D369040F044B6E9561765C356907D3 | [e-mail] | Foo          |
+----------------------------------+-----------------+--------------+

基于此，下面的补丁程序应用于MySQLDriver.scala（版本1.0.1）效果很好：

$ 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("-", "")+"'"
     }
   }
 }

使用这个功能，你可以编写如下代码：

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
}

我不确定您正在使用哪个数据库，但类似的方法可能有效。我还没有对此进行性能测试。

将UUID编码为字节数组

有几种选项可以避免代码修补。

使用http://nineofclouds.blogspot.com.au/2013/04/storing-uuids-with-anorm.html中的UUIDHelper，您可以将UUID编码为字节数组并执行静态查询。有些不太优雅，但可行的方式是：

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.

将UUID编码为十六进制字符串

下面的方法可能不是最优雅的，但是出于完整性考虑而包含在内:

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

编辑：下面是针对主分支的拉取请求。请注意，此拉取请求针对主分支（2.0.0），但我仅在1.0.1上成功测试过。

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

- Andrew E