#73 Deconstructing on Joins

src/main/scala/usql/dao/QueryBuilder.scala

@@ -18,7 +18,7 @@ trait QueryBuilder[T] extends Query[T] {
     project(f(columnRootPath))
   }
 
-  protected def columnRootPath: ColumnRootPath[T] = ColumnPath.make(using structure)
+  private[usql] def columnRootPath: ColumnRootPath[T] = ColumnPath.make(using structure)
 
   /** Project using a Column Path */
   def project[P](p: ColumnPath[T, P]): QueryBuilder[P]
@@ -74,4 +74,65 @@ object QueryBuilder {
   def make[T](using tabular: SqlTabular[T]): QueryBuilderForTable[T] = {
     SimpleTableSelect(tabular)
   }
+
+  extension [A, B](qb: QueryBuilder[(A, B)])
+    def map[P](
+        f: (ColumnPath[(A, B), A], ColumnPath[(A, B), B]) => ColumnPath[(A, B), P]
+    ): QueryBuilder[P] = {
+      val root = qb.columnRootPath
+      val a    = root.selectDynamic("_1").asInstanceOf[ColumnPath[(A, B), A]]
+      val b    = root.selectDynamic("_2").asInstanceOf[ColumnPath[(A, B), B]]
+      qb.project(f(a, b))
+    }
+
+  extension [A, B, C](qb: QueryBuilder[(A, B, C)])
+    def map[P](
+        f: (
+            ColumnPath[(A, B, C), A],
+            ColumnPath[(A, B, C), B],
+            ColumnPath[(A, B, C), C]
+        ) => ColumnPath[(A, B, C), P]
+    ): QueryBuilder[P] = {
+      val root = qb.columnRootPath
+      val a    = root.selectDynamic("_1").asInstanceOf[ColumnPath[(A, B, C), A]]
+      val b    = root.selectDynamic("_2").asInstanceOf[ColumnPath[(A, B, C), B]]
+      val c    = root.selectDynamic("_3").asInstanceOf[ColumnPath[(A, B, C), C]]
+      qb.project(f(a, b, c))
+    }
+
+  extension [A, B, C, D](qb: QueryBuilder[(A, B, C, D)])
+    def map[P](
+        f: (
+            ColumnPath[(A, B, C, D), A],
+            ColumnPath[(A, B, C, D), B],
+            ColumnPath[(A, B, C, D), C],
+            ColumnPath[(A, B, C, D), D]
+        ) => ColumnPath[(A, B, C, D), P]
+    ): QueryBuilder[P] = {
+      val root = qb.columnRootPath
+      val a    = root.selectDynamic("_1").asInstanceOf[ColumnPath[(A, B, C, D), A]]
+      val b    = root.selectDynamic("_2").asInstanceOf[ColumnPath[(A, B, C, D), B]]
+      val c    = root.selectDynamic("_3").asInstanceOf[ColumnPath[(A, B, C, D), C]]
+      val d    = root.selectDynamic("_4").asInstanceOf[ColumnPath[(A, B, C, D), D]]
+      qb.project(f(a, b, c, d))
+    }
+
+  extension [A, B, C, D, E](qb: QueryBuilder[(A, B, C, D, E)])
+    def map[P](
+        f: (
+            ColumnPath[(A, B, C, D, E), A],
+            ColumnPath[(A, B, C, D, E), B],
+            ColumnPath[(A, B, C, D, E), C],
+            ColumnPath[(A, B, C, D, E), D],
+            ColumnPath[(A, B, C, D, E), E]
+        ) => ColumnPath[(A, B, C, D, E), P]
+    ): QueryBuilder[P] = {
+      val root = qb.columnRootPath
+      val a    = root.selectDynamic("_1").asInstanceOf[ColumnPath[(A, B, C, D, E), A]]
+      val b    = root.selectDynamic("_2").asInstanceOf[ColumnPath[(A, B, C, D, E), B]]
+      val c    = root.selectDynamic("_3").asInstanceOf[ColumnPath[(A, B, C, D, E), C]]
+      val d    = root.selectDynamic("_4").asInstanceOf[ColumnPath[(A, B, C, D, E), D]]
+      val e    = root.selectDynamic("_5").asInstanceOf[ColumnPath[(A, B, C, D, E), E]]
+      qb.project(f(a, b, c, d, e))
+    }
 }

src/test/scala/usql/dao/QueryBuilderTest.scala

@@ -129,6 +129,33 @@ class QueryBuilderTest extends TestBaseWithH2 {
     foo.count() shouldBe 3
   }
 
+  it should "support tuple-destructured map after a single join" in new EnvWithSamples {
+    val foo: QueryBuilder[(Person, Int)] = Person.query
+      .join(PersonPermission.query)(_.id === _.personId)
+      .map((p, pp) => (p, pp.permissionId))
+    foo.all() should contain theSameElementsAs Seq(
+      alice -> read.id,
+      alice -> write.id,
+      bob   -> read.id
+    )
+
+    foo.count() shouldBe 3
+  }
+
+  it should "support tuple-destructured map after a left join" in new EnvWithSamples {
+    val q = Person.query
+      .leftJoin(PersonPermission.query)(_.id === _.personId)
+      .leftJoin(Permission.query)(_._2.permissionId === _.id)
+      .map((pp, perm) => (pp._1.name, perm.name))
+
+    q.all() should contain theSameElementsAs Seq(
+      ("Alice", Some("Read")),
+      ("Alice", Some("Write")),
+      ("Bob", Some("Read")),
+      ("Charly", None)
+    )
+  }
+
   it should "with simple joins" in new EnvWithSamples {
     val foo = Person.query
       .join(PersonPermission.query)(_.id === _.personId)