如何在 Slick 中使用 LIKE 运算符？

Question

I am trying to use Slick framework for integration with MySQL . However whenever I use LIKE operator it fails with the error, as shown below.

Code

.filterIf(etilizeRequest.q.nonEmpty) {
    case ((((((prod, manRep), catRep), cnRep), pdRep), prodSkusRep), saRep) =>
        cnRep.map(_.name).like("%"+etilizeRequest.q.get+"%").get
}

Error

slick.SlickException: Caught exception while computing default value for Rep[Option[_]].getOrElse -- This cannot be done lazily when the value is needed on the database side at slick.compiler.HoistClientOps$$anonfun$rewriteDBSide$1.applyOrElse(HoistClientOps.scala:159) at slick.compiler.HoistClientOps$$anonfun$rewriteDBSide$1.applyOrElse(HoistClientOps.scala:152) at slick.ast.NodeOps$.r$1(Util.scala:47) at slick.ast.NodeOps$.$anonfun$replace$2(Util.scala:48) at slick.ast.BinaryNode.mapChildren(Node.scala:204) at slick.ast.BinaryNode.mapChildren$(Node.scala:200) at slick.ast.Filter.mapChildren(Node.scala:310) at slick.ast.NodeOps$.g$1(Util.scala:48) at slick.ast.NodeOps$.r$1(Util.scala:47) at slick.ast.NodeOps$.$anonfun$replace$2(Util.scala:48) Caused by: slick.SlickException: Read NULL value for column slick.lifted.OptionColumnExtensionMethods@594b5a63 at slick.lifted.OptionColumnExtensionMethods$.$anonfun$get$1(ExtensionMethods.scala:39) at slick.compiler.HoistClientOps$$anonfun$rewri teDBSide$1.applyOrElse(HoistClientOps.scala:156) at slick.compiler.HoistClientOps$$anonfun$rewriteDBSide$1.applyOrElse(HoistClientOps.scala:152) at slick.ast.NodeOps$.r$1(Util.scala:47) at slick.ast.NodeOps$.$anonfun$replace$2(Util.scala:48) at slick.ast.BinaryNode.mapChildren(Node.scala:204) at slick.ast.BinaryNode.mapChildren$(Node.scala:200) at slick.ast.Filter.mapChildren(Node.scala:310) at slick.ast.NodeOps$.g$1(Util.scala:48) at slick.ast.NodeOps$.r$1(Util.scala:47)

Can someonw suggest the reasoning behind this error and how can I fix it ?

Answer 1

Slick can't always call .get on an Option when the .get happens at the SQL level. It's not clear to me when this happens, but in your example I'd guess it will be the final .get at the end. I think that because we'd be asking, at the database level, to turn an optional like expression into SQL. I don't think that's possible.

In your case there's a work around to convert an optional column to a string column:

cnRep.map(_.name).asColumnOf[String].like(...etc...)

...and you can omit the final .get call. (I actually thought automatic support for this was added in Slick 3.3, but I guess not).

You may also be able to use filterOpt rather than filterIf . That would remove one more get from inside your LIKE expression. Section 2.9 of Essential Slick gives some examples.