title: Scala Slick: MappedColumnType cannot find implicit value for BaseColumlnType[String]
body: <p>I'm trying to set up database columns in Slick with non-primitive objects. I've spent the past day researching MappedColumnType for mapping custom objects to columns, and as far as I can tell I'm implementing them as people recommend. Unfortunately, the following code produces an error:</p>
  
  <pre><code>  implicit val localDateMapper = MappedColumnType.base[LocalDate, String]
      (
      //map date to String
      d =&gt; d.toString,
      //map String to date
      s =&gt; LocalDate.parse(s)
      )
  </code></pre>
  
  <p>And here is the error:</p>
  
  <pre><code>could not find implicit value for evidence parameter of type slick.driver.H2Driver.BaseColumnType[String]
  </code></pre>
  
  <p>I've seen multiple examples where people map custom objects to and from Strings. I figure there must be something I'm missing?</p>
  
  <p>For reference, I'm using Play Slick 1.1.1 and Scala 2.11.6. The former supports Slick 3.1.</p>