title: JPA spring data specification on joins
body: <p>I have some already created org.springframework.data.jpa.domain.Specifications. Now I am creating a query in which I would like to use the specification on a table that I join to. But in order to use a Specification I need a Root, but joining gives me a Join object.</p>
  
  <p>Is there a way of converting from a Join object to a Root? Or is there something analogous to Specification, but for Joins?</p>