Hide `IdOnlyAggregateReference` class.

IdOnlyAggregateReference is an implementation detail of AggregateReference.

Closes #2106

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/core/mapping/AggregateReference.java

@@ -15,11 +15,6 @@
  */
 package org.springframework.data.jdbc.core.mapping;
 
-import java.util.Objects;
-
-import org.springframework.lang.Nullable;
-import org.springframework.util.Assert;
-
 /**
  * A reference to the aggregate root of a different aggregate.
  *
@@ -49,47 +44,4 @@ public interface AggregateReference<T, ID> {
 	 */
 	ID getId();
 
-	/**
-	 * An {@link AggregateReference} that only holds the id of the referenced aggregate root. Note that there is no check
-	 * that a matching aggregate for this id actually exists.
-	 *
-	 * @param <T>
-	 * @param <ID>
-	 */
-	class IdOnlyAggregateReference<T, ID> implements AggregateReference<T, ID> {
-
-		private final ID id;
-
-		public IdOnlyAggregateReference(ID id) {
-
-			Assert.notNull(id, "Id must not be null");
-			this.id = id;
-		}
-
-		@Override
-		public ID getId() {
-			return id;
-		}
-
-		@Override
-		public boolean equals(@Nullable Object o) {
-
-			if (this == o)
-				return true;
-			if (o == null || getClass() != o.getClass())
-				return false;
-			IdOnlyAggregateReference<?, ?> that = (IdOnlyAggregateReference<?, ?>) o;
-			return id.equals(that.id);
-		}
-
-		@Override
-		public int hashCode() {
-			return Objects.hash(id);
-		}
-
-		@Override
-		public String toString() {
-			return "IdOnlyAggregateReference{" + "id=" + id + '}';
-		}
-	}
 }

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/core/mapping/IdOnlyAggregateReference.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2025 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.jdbc.core.mapping;
+
+import org.springframework.util.Assert;
+
+/**
+ * An {@link AggregateReference} that only holds the id of the referenced aggregate root. Note that there is no check
+ * that a matching aggregate for this id actually exists.
+ *
+ * @author Jens Schauder
+ * @author Mark Paluch
+ * @since 4.0
+ * @param <T>
+ * @param <ID>
+ */
+record IdOnlyAggregateReference<T, ID>(ID id) implements AggregateReference<T, ID> {
+
+	IdOnlyAggregateReference {
+		Assert.notNull(id, "Id must not be null");
+	}
+
+	@Override
+	public ID getId() {
+		return id();
+	}
+
+	@Override
+	public String toString() {
+		return "IdOnlyAggregateReference{" + "id=" + id + '}';
+	}
+}

spring-data-jdbc/src/test/java/org/springframework/data/jdbc/core/mapping/IdOnlyAggregateReferenceTest.java

@@ -3,17 +3,16 @@ package org.springframework.data.jdbc.core.mapping;
 import static org.assertj.core.api.Assertions.*;
 
 import org.junit.jupiter.api.Test;
-import org.springframework.data.jdbc.core.mapping.AggregateReference.IdOnlyAggregateReference;
 
 /**
  * Unit tests for the {@link IdOnlyAggregateReference}.
  *
  * @author Myeonghyeon Lee
  */
-public class IdOnlyAggregateReferenceTest {
+class IdOnlyAggregateReferenceTest {
 
 	@Test // DATAJDBC-427
-	public void equals() {
+	void equals() {
 
 		AggregateReference<DummyEntity, String> reference1 = AggregateReference.to("1");
 		AggregateReference<DummyEntity, String> reference2 = AggregateReference.to("1");
@@ -23,7 +22,7 @@ public class IdOnlyAggregateReferenceTest {
 	}
 
 	@Test // DATAJDBC-427
-	public void equalsFalse() {
+	void equalsFalse() {
 
 		AggregateReference<DummyEntity, String> reference1 = AggregateReference.to("1");
 		AggregateReference<DummyEntity, String> reference2 = AggregateReference.to("2");
@@ -33,7 +32,7 @@ public class IdOnlyAggregateReferenceTest {
 	}
 
 	@Test // DATAJDBC-427
-	public void hashCodeTest() {
+	void hashCodeTest() {
 
 		AggregateReference<DummyEntity, String> reference1 = AggregateReference.to("1");
 		AggregateReference<DummyEntity, String> reference2 = AggregateReference.to("1");