I tried it by simply adding
Cats.ddl.create
Cats.filter(_.name===cat.name).delete
to play-slick-cake-sample/app/controllers/Application.scala
. Works fine for me.
Looks like you are using the wrong imports. Look at https://github.com/freekh/play-slick/blob/master/samples/play-slick-sample/app/controllers/Application.scala and mimic the imports.