Add the condition function by the primary key.

src/main/scala/model/IssueLabels.scala

@@ -4,6 +4,8 @@ import scala.slick.driver.H2Driver.simple._
 
 object IssueLabels extends Table[IssueLabel]("ISSUE_LABEL") with IssueTemplate with LabelTemplate {
   def * = userName ~ repositoryName ~ issueId ~ labelId <> (IssueLabel, IssueLabel.unapply _)
+  def byPrimaryKey(owner: String, repository: String, issueId: Int, labelId: Int) =
+    byIssue(owner, repository, issueId) && (this.labelId is labelId.bind)
 }
 
 case class IssueLabel(