I use slick 2.0.1

My case class is：

   case class IdentityId(userId: String, providerId: String)
   case class IdentityItem (
   userId:String,
   providerID: String,
   ....
   ){
   def identityId=IdentityId(userId,providerID)
  }

userId is the foreign key of user table, providerID is the foreign key of provider table, for avoid composite primary keys, I decide add another column name identityId.

you should know that in default slick use only constructed field as the datatable column. In this case I want to use additional column "identityId".