Add support for self (left / right / inner / cross) join (#292)

* Added crossSelfJoin, innerSelfJoin, leftOuterSelfJoin, rightOuterSelfJoin + Tests + Comments + Readme

* Changes as discussed in #292

README.md

@@ -41,6 +41,9 @@ Seq.of(1, 2, 3, 4).containsAny(2, 5);
 // (tuple(1, "A"), tuple(1, "B"), tuple(2, "A"), tuple(2, "B"))
 Seq.of(1, 2).crossJoin(Seq.of("A", "B"));
 
+// (tuple(1, 1), tuple(1, 2), tuple(2, 1), tuple(2, 2))
+Seq.of(1, 2).crossSelfJoin()
+
 // (1, 2, 3, 1, 2, 3, 1, 2, 3, 1, 2, ...)
 Seq.of(1, 2, 3).cycle();
 
@@ -62,6 +65,9 @@ Seq.of(1, 2, 3, 4).grouped(i -> i % 2);
 // (tuple(1, 1), tuple(2, 2))
 Seq.of(1, 2, 4).innerJoin(Seq.of(1, 2, 3), (a, b) -> a == b);
 
+// (tuple(1, 2), tuple(2, 1))
+Seq.of(1, 2).innerSelfJoin((t, u) -> t != u)
+
 // (1, 0, 2, 0, 3, 0, 4)
 Seq.of(1, 2, 3, 4).intersperse(0);
 
@@ -77,6 +83,9 @@ Seq.of(1, 2, 3).join("|", "^", "$");
 // (tuple(1, 1), tuple(2, 2), tuple(4, null))
 Seq.of(1, 2, 4).leftOuterJoin(Seq.of(1, 2, 3), (a, b) -> a == b);
 
+// (tuple(tuple(1, 0), NULL), tuple(tuple(2, 1), tuple(1, 0)))
+Seq.of(tuple(1, 0), tuple(2, 1)).leftOuterSelfJoin((t, u) -> t.v2 == u.v1)
+
 // (1, 2)
 Seq.of(1, 2, 3, 4, 5).limitWhile(i -> i < 3);
 
@@ -89,6 +98,9 @@ Seq.of(new Object(), 1, "B", 2L).ofType(Number.class);
 // (tuple(1, 1), tuple(2, 2), tuple(null, 3))
 Seq.of(1, 2, 4).rightOuterJoin(Seq.of(1, 2, 3), (a, b) -> a == b);
 
+// (tuple(NULL, tuple(1, 0)), tuple(tuple(1, 0), tuple(2, 1)))
+Seq.of(tuple(1, 0), tuple(2, 1)).rightOuterSelfJoin((t, u) -> t.v2 == u.v1)
+
 // tuple((1, 3), (2, 4))
 Seq.of(1, 2, 3, 4).partition(i -> i % 2 != 0);
 

src/main/java/org/jooq/lambda/Seq.java

@@ -202,6 +202,22 @@ default <U> Seq<Tuple2<T, U>> crossJoin(Seq<? extends U> other) {
         return Seq.crossJoin(this, other);
     }
 
+    /**
+     * Cross join stream with itself into one.
+     * <p>
+     * <code><pre>
+     * // (tuple(1, 1), tuple(1, 2), tuple(2, 1), tuple(2, 2))
+     * Seq.of(1, 2).crossSelfJoin()
+     * </pre></code>
+     */
+    default Seq<Tuple2<T, T>> crossSelfJoin() {
+
+        // This algorithm isn't lazy and has substantial complexity for large argument streams!
+        List<? extends T> list = toList();
+
+        return Seq.crossJoin(seq(list), seq(list));
+    }
+
     /**
      * Inner join 2 streams into one.
      * <p>
@@ -245,6 +261,22 @@ default <U> Seq<Tuple2<T, U>> innerJoin(Seq<? extends U> other, BiPredicate<? su
               .onClose(other::close);
     }
 
+    /**
+     * Inner join stream with itself.
+     * <p>
+     * <code><pre>
+     * // (tuple(1, 1), tuple(2, 2))
+     * Seq.of(1, 2).innerSelfJoin((t, u) -> Objects.equals(t, u))
+     * </pre></code>
+     */
+    default Seq<Tuple2<T, T>> innerSelfJoin(BiPredicate<? super T, ? super T> predicate) {
+
+        // This algorithm isn't lazy and has substantial complexity for large argument streams!
+        List<? extends T> list = toList();
+
+        return seq(list).innerJoin(seq(list), predicate);
+    }
+
     /**
      * Left outer join 2 streams into one.
      * <p>
@@ -289,6 +321,22 @@ default <U> Seq<Tuple2<T, U>> leftOuterJoin(Seq<? extends U> other, BiPredicate<
               .onClose(other::close);
     }
 
+    /**
+     * Left outer join one streams into itself.
+     * <p>
+     * <code><pre>
+     * // (tuple(tuple(1, 0), NULL), tuple(tuple(2, 1), tuple(1, 0)))
+     * Seq.of(new Tuple2<Integer, Integer>(1, 0), new Tuple2<Integer, Integer>(2, 1)).leftOuterSelfJoin((t, u) -> Objects.equals(t.v2, u.v1))
+     * </pre></code>
+     */
+    default Seq<Tuple2<T, T>> leftOuterSelfJoin(BiPredicate<? super T, ? super T> predicate) {
+
+        // This algorithm isn't lazy and has substantial complexity for large argument streams!
+        List<? extends T> list = toList();
+
+        return seq(list).leftOuterJoin(seq(list), predicate);
+    }
+
     /**
      * Right outer join 2 streams into one.
      * <p>
@@ -328,6 +376,19 @@ default <U> Seq<Tuple2<T, U>> rightOuterJoin(Seq<? extends U> other, BiPredicate
               .onClose(other::close);
     }
 
+    /**
+     * Right outer join stream into itself.
+     * <p>
+     * <code><pre>
+     * // (tuple(NULL, tuple(1, 0)), tuple(tuple(1, 0), tuple(2, 1)))
+     * Seq.of(new Tuple2<Integer, Integer>(1, 0), new Tuple2<Integer, Integer>(2, 1)).rightOuterSelfJoin((t, u) -> Objects.equals(t.v2, u.v1))
+     * </pre></code>
+     */
+    default Seq<Tuple2<T, T>> rightOuterSelfJoin(BiPredicate<? super T, ? super T> predicate) {
+        return leftOuterSelfJoin((u, t) -> predicate.test(t, u))
+              .map(t -> tuple(t.v2, t.v1));
+    }
+
     /**
      * Produce this stream, or an alternative stream from the
      * <code>value</code>, in case this stream is empty.

src/test/java/org/jooq/lambda/SeqTest.java

@@ -798,6 +798,39 @@ public void testCrossJoin() {
             ).toList());
     }
 
+    @Test
+    public void testCrossSelfJoin() {
+
+        // {A} x {B}
+        // ---------------------------------------------------------------------
+        assertEquals(asList(),
+            Seq.of().crossSelfJoin().toList());
+
+        assertEquals(asList(
+            tuple(1, 1)),
+            Seq.of(1).crossSelfJoin().toList());
+
+        assertEquals(asList(
+            tuple(1, 1),
+            tuple(1, 2),
+            tuple(2, 1),
+            tuple(2, 2)),
+            Seq.of(1, 2).crossSelfJoin().toList());
+
+        assertEquals(asList(
+            tuple(1, 1),
+            tuple(1, 2),
+            tuple(1, 3),
+            tuple(2, 1),
+            tuple(2, 2),
+            tuple(2, 3),
+            tuple(3, 1),
+            tuple(3, 2),
+            tuple(3, 3)),
+            Seq.of(1, 2, 3).crossSelfJoin().toList());
+
+    }
+
     @Test
     public void testInnerJoin() {
         BiPredicate<Object, Object> TRUE = (t, u) -> true;
@@ -828,6 +861,23 @@ public void testInnerJoin() {
             Seq.<Object>of(1).innerJoin(Seq.of(1, 2), TRUE).toList());
     }
 
+    @Test
+    public void testInnerSelfJoin() {
+        BiPredicate<Object, Object> TRUE = (t, u) -> true;
+
+        assertEquals(asList(),
+            Seq.of().innerSelfJoin(TRUE).toList());
+
+        assertEquals(asList(
+            tuple(1, 1),
+            tuple(2, 2)),
+            Seq.of(1, 2).innerSelfJoin((t, u) -> t == u).toList());
+
+        assertEquals(asList(
+            tuple(1, 2)),
+            Seq.of(1, 2).innerSelfJoin((t, u) -> t * 2 == u).toList());
+    }
+
     @Test
     public void testLeftOuterJoin() {
         BiPredicate<Object, Object> TRUE = (t, u) -> true;
@@ -860,6 +910,19 @@ public void testLeftOuterJoin() {
             Seq.<Object>of(1).leftOuterJoin(Seq.of(1, 2), TRUE).toList());
     }
 
+    @Test
+    public void testLeftOuterSelfJoin() {
+        BiPredicate<Object, Object> TRUE = (t, u) -> true;
+
+        assertEquals(asList(),
+            Seq.of().leftOuterSelfJoin(TRUE).toList());
+
+        assertEquals(asList(
+            tuple(tuple(1, 0), (Tuple2<Integer, Integer>) null),
+            tuple(tuple(2, 1), tuple(1,0))),
+            Seq.of(tuple(1, 0), tuple(2, 1)).leftOuterSelfJoin((t, u) -> t.v2 == u.v1).toList());
+    }
+
     @Test
     public void testRightOuterJoin() {
         BiPredicate<Object, Object> TRUE = (t, u) -> true;
@@ -896,6 +959,19 @@ public void testRightOuterJoin() {
             Seq.<Object>of(1).rightOuterJoin(Seq.of(1, 2), TRUE).toList());
     }
 
+    @Test
+    public void testRightOuterSelfJoin() {
+        BiPredicate<Object, Object> TRUE = (t, u) -> true;
+
+        assertEquals(asList(),
+            Seq.of().rightOuterSelfJoin(TRUE).toList());
+
+        assertEquals(asList(
+            tuple((Tuple2<Integer, Integer>) null, tuple(1, 0)),
+            tuple(tuple(1,0), tuple(2, 1))),
+            Seq.of(tuple(1, 0), tuple(2, 1)).rightOuterSelfJoin((t, u) -> t.v1 == u.v2).toList());
+    }
+
     @Test
     public void testOnEmpty() throws X {
         assertEquals(asList(1), Seq.of().onEmpty(1).toList());