Refactor JPQL predicate composition by flattening AND/OR.

Signed-off-by: l2yuPa <jeungwon28@gmail.com>
Closes #4195

Author: l2yujw

spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/query/JpqlQueryBuilder.java

@@ -27,6 +27,7 @@
 import java.util.Map;
 import java.util.Objects;
 import java.util.function.Supplier;
+import java.util.stream.Collectors;
 
 import org.jspecify.annotations.Nullable;
 
@@ -44,6 +45,7 @@
  *
  * @author Mark Paluch
  * @author Choi Wang Gyu
+ * @author Jeongwon Ryu
  * @since 4.0
  */
 @SuppressWarnings("JavadocDeclaration")
@@ -710,7 +712,23 @@ public interface Predicate extends Renderable {
 		@Contract("_ -> new")
 		@CheckReturnValue
 		default Predicate or(Predicate other) {
-			return new OrPredicate(this, other);
+
+			// Flatten OR composition: Or([a,b]).or(c) -> Or([a,b,c])
+			List<Predicate> parts = new ArrayList<>();
+
+			if (this instanceof OrPredicate op) {
+				parts.addAll(op.parts());
+			} else {
+				parts.add(this);
+			}
+
+			if (other instanceof OrPredicate op) {
+				parts.addAll(op.parts());
+			} else {
+				parts.add(other);
+			}
+
+			return new OrPredicate(parts);
 		}
 
 		/**
@@ -721,8 +739,27 @@ default Predicate or(Predicate other) {
 		 */
 		@Contract("_ -> new")
 		@CheckReturnValue
-		default Predicate and(Predicate other) { // don't like the structuring of this and the nest() thing
-			return new AndPredicate(this, other);
+		default Predicate and(Predicate other) {
+
+			// don't like the structuring of this and the nest() thing
+			//
+			// Flatten AND composition to avoid deep nesting:
+			// And([a,b]).and(c) -> And([a,b,c])
+			List<Predicate> parts = new ArrayList<>();
+
+			if (this instanceof AndPredicate ap) {
+				parts.addAll(ap.parts());
+			} else {
+				parts.add(this);
+			}
+
+			if (other instanceof AndPredicate ap) {
+				parts.addAll(ap.parts());
+			} else {
+				parts.add(other);
+			}
+
+			return new AndPredicate(parts);
 		}
 
 		/**
@@ -1526,32 +1563,68 @@ private static boolean hasParenthesis(String str) {
 
 	}
 
-	record AndPredicate(Predicate left, Predicate right) implements Predicate {
+	record AndPredicate(List<Predicate> parts) implements Predicate {
+
+		AndPredicate {
+
+			Assert.notEmpty(parts, "Predicate parts must not be empty");
+
+			// Flatten nested AND predicates to keep the internal representation normalized.
+			List<Predicate> flattened = new ArrayList<>(parts.size());
+			for (Predicate p : parts) {
+				if (p instanceof AndPredicate ap) {
+					flattened.addAll(ap.parts());
+				} else {
+					flattened.add(p);
+				}
+			}
+
+			parts = List.copyOf(flattened);
+		}
 
 		@Override
 		public String render(RenderContext context) {
-			return "%s AND %s".formatted(left.render(context), right.render(context));
+			return parts.stream()
+					.map(p -> p.render(context))
+					.collect(Collectors.joining(" AND "));
 		}
 
 		@Override
 		public String toString() {
 			return render(RenderContext.EMPTY);
 		}
-
 	}
 
-	record OrPredicate(Predicate left, Predicate right) implements Predicate {
+	record OrPredicate(List<Predicate> parts) implements Predicate {
+
+		OrPredicate {
+
+			Assert.notEmpty(parts, "Predicate parts must not be empty");
+
+			// Flatten nested OR predicates to keep the internal representation normalized.
+			List<Predicate> flattened = new ArrayList<>(parts.size());
+			for (Predicate p : parts) {
+				if (p instanceof OrPredicate op) {
+					flattened.addAll(op.parts());
+				} else {
+					flattened.add(p);
+				}
+			}
+
+			parts = List.copyOf(flattened);
+		}
 
 		@Override
 		public String render(RenderContext context) {
-			return "%s OR %s".formatted(left.render(context), right.render(context));
+			return parts.stream()
+					.map(p -> p.render(context))
+					.collect(Collectors.joining(" OR "));
 		}
 
 		@Override
 		public String toString() {
 			return render(RenderContext.EMPTY);
 		}
-
 	}
 
 	record NestedPredicate(Predicate delegate) implements Predicate {

spring-data-jpa/src/test/java/org/springframework/data/jpa/repository/query/JpqlQueryBuilderUnitTests.java

@@ -45,6 +45,7 @@
  * @author Christoph Strobl
  * @author Mark Paluch
  * @author Choi Wang Gyu
+ * @author Jeongwon Ryu
  */
 class JpqlQueryBuilderUnitTests {
 
@@ -180,6 +181,41 @@ void inPredicateWithNestedExpression() {
 				.isEqualTo("o.country IN (SELECT c.code FROM Country c WHERE c.active = true)");
 	}
 
+	@Test
+	void chainedAndRendersWithoutExtraParentheses() {
+
+		Entity entity = entity(LineItem.class);
+
+		Join p = innerJoin(entity, "product");
+		Join p0 = innerJoin(entity, "product2");
+
+		PathAndOrigin aPath = path(p, "name");
+		PathAndOrigin bPath = path(p0, "name");
+
+		Predicate a = where(aPath).eq(literal("ex30"));
+		Predicate b = where(bPath).eq(literal("ex40"));
+		Predicate c = where(aPath).isNotNull();
+
+		String fragment = a.and(b).and(c).render(ctx(entity));
+
+		assertThat(fragment).isEqualTo("p.name = 'ex30' AND p_0.name = 'ex40' AND p.name IS NOT NULL");
+	}
+
+	@Test
+	void chainedOrRendersWithoutExtraParentheses() {
+
+		Entity entity = entity(Order.class);
+		PathAndOrigin id = path(entity, "id");
+
+		Predicate a = where(id).eq(literal("1"));
+		Predicate b = where(id).eq(literal("2"));
+		Predicate c = where(id).eq(literal("3"));
+
+		String fragment = a.or(b).or(c).render(ctx(entity));
+
+		assertThat(fragment).isEqualTo("o.id = '1' OR o.id = '2' OR o.id = '3'");
+	}
+
 	@Test // GH-3588
 	void selectRendering() {