Added more join examples

modules/slick/src/main/scala/com/example/user/slick/dbios/SlickLibraryDbio.scala

@@ -95,11 +95,27 @@ class SlickLibraryDbio extends Tables {
         author <- Authors filter (_.id === authorId)
       } yield (author, book)
 
-    // lazy val authorOfBook3 = (bookId: Long) =>
-    //   for {
-    //     authorId <- bookById(bookId).map(_.map(_.authorId))
-    //     (authors) <- Authors filter (_.id === authorId)
-    //   } yield (authors)
+    lazy val authorOfBook3 = (bookId: Long) =>
+      for {
+        (author, book) <- Authors join
+          Books on (_.id === _.authorId) filter {
+          case (authors, books) => books.id === bookId
+        } map {
+          case (authors, books) =>
+            (authors.id, authors.name).mapTo[Author] -> (
+              books.title,
+              books.authorId,
+              books.createdAt
+            ).mapTo[BookDTO]
+        }
+      } yield (author, book)
+
+      lazy val authorOfBook4 = (bookId: Long) =>
+      for {
+        book <- Books
+        author <- book.authorsFk
+      } yield (author, book)
+    
   }
   case class BookWithoutId(title: String, authorId: Long)
   // def test() = {