Extract a ReadOnlyRepository between Repository and CrudRepository.

Gather read-only, i.e. "safe" operations into a separate interface, giving users a clear ability to define such repositories themselves.

Closes #2610, #2064.

src/main/java/org/springframework/data/repository/CrudRepository.java

@@ -25,7 +25,7 @@
  * @author Jens Schauder
  */
 @NoRepositoryBean
-public interface CrudRepository<T, ID> extends Repository<T, ID> {
+public interface CrudRepository<T, ID> extends ReadOnlyRepository<T, ID> {
 
 	/**
 	 * Saves a given entity. Use the returned instance for further operations as the save operation might have changed the
@@ -48,52 +48,6 @@ public interface CrudRepository<T, ID> extends Repository<T, ID> {
 	 */
 	<S extends T> Iterable<S> saveAll(Iterable<S> entities);
 
-	/**
-	 * Retrieves an entity by its id.
-	 *
-	 * @param id must not be {@literal null}.
-	 * @return the entity with the given id or {@literal Optional#empty()} if none found.
-	 * @throws IllegalArgumentException if {@literal id} is {@literal null}.
-	 */
-	Optional<T> findById(ID id);
-
-	/**
-	 * Returns whether an entity with the given id exists.
-	 *
-	 * @param id must not be {@literal null}.
-	 * @return {@literal true} if an entity with the given id exists, {@literal false} otherwise.
-	 * @throws IllegalArgumentException if {@literal id} is {@literal null}.
-	 */
-	boolean existsById(ID id);
-
-	/**
-	 * Returns all instances of the type.
-	 *
-	 * @return all entities
-	 */
-	Iterable<T> findAll();
-
-	/**
-	 * Returns all instances of the type {@code T} with the given IDs.
-	 * <p>
-	 * If some or all ids are not found, no entities are returned for these IDs.
-	 * <p>
-	 * Note that the order of elements in the result is not guaranteed.
-	 *
-	 * @param ids must not be {@literal null} nor contain any {@literal null} values.
-	 * @return guaranteed to be not {@literal null}. The size can be equal or less than the number of given
-	 *         {@literal ids}.
-	 * @throws IllegalArgumentException in case the given {@link Iterable ids} or one of its items is {@literal null}.
-	 */
-	Iterable<T> findAllById(Iterable<ID> ids);
-
-	/**
-	 * Returns the number of entities available.
-	 *
-	 * @return the number of entities.
-	 */
-	long count();
-
 	/**
 	 * Deletes the entity with the given id.
 	 *

src/main/java/org/springframework/data/repository/ReadOnlyRepository.java

@@ -0,0 +1,74 @@
+/*
+ * Copyright 2011-2022 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.repository;
+
+import java.util.Optional;
+
+/**
+ * Interface for read-only CRUD operations on a repository for a specific type.
+ *
+ * @author Greg Turnquist
+ * @since 3.0
+ */
+@NoRepositoryBean
+public interface ReadOnlyRepository<T, ID> extends Repository<T, ID> {
+
+	/**
+	 * Retrieves an entity by its id.
+	 *
+	 * @param id must not be {@literal null}.
+	 * @return the entity with the given id or {@literal Optional#empty()} if none found.
+	 * @throws IllegalArgumentException if {@literal id} is {@literal null}.
+	 */
+	Optional<T> findById(ID id);
+
+	/**
+	 * Returns whether an entity with the given id exists.
+	 *
+	 * @param id must not be {@literal null}.
+	 * @return {@literal true} if an entity with the given id exists, {@literal false} otherwise.
+	 * @throws IllegalArgumentException if {@literal id} is {@literal null}.
+	 */
+	boolean existsById(ID id);
+
+	/**
+	 * Returns all instances of the type.
+	 *
+	 * @return all entities
+	 */
+	Iterable<T> findAll();
+
+	/**
+	 * Returns all instances of the type {@code T} with the given IDs.
+	 * <p>
+	 * If some or all ids are not found, no entities are returned for these IDs.
+	 * <p>
+	 * Note that the order of elements in the result is not guaranteed.
+	 *
+	 * @param ids must not be {@literal null} nor contain any {@literal null} values.
+	 * @return guaranteed to be not {@literal null}. The size can be equal or less than the number of given
+	 *         {@literal ids}.
+	 * @throws IllegalArgumentException in case the given {@link Iterable ids} or one of its items is {@literal null}.
+	 */
+	Iterable<T> findAllById(Iterable<ID> ids);
+
+	/**
+	 * Returns the number of entities available.
+	 *
+	 * @return the number of entities.
+	 */
+	long count();
+}

src/test/java/org/springframework/data/repository/core/support/DefaultCrudMethodsUnitTests.java

@@ -28,6 +28,7 @@
 import org.springframework.data.domain.Sort;
 import org.springframework.data.repository.CrudRepository;
 import org.springframework.data.repository.PagingAndSortingRepository;
+import org.springframework.data.repository.ReadOnlyRepository;
 import org.springframework.data.repository.Repository;
 import org.springframework.data.repository.core.CrudMethods;
 import org.springframework.data.repository.core.RepositoryInformation;
@@ -111,10 +112,10 @@ void detectsOverloadedMethodsCorrectly() throws Exception {
 	void ignoresWrongOverloadedMethods() throws Exception {
 
 		var type = RepositoryWithAllCrudMethodOverloadedWrong.class;
-		assertFindOneMethodOn(type, CrudRepository.class.getDeclaredMethod("findById", Object.class));
+		assertFindOneMethodOn(type, ReadOnlyRepository.class.getDeclaredMethod("findById", Object.class));
 		assertDeleteMethodOn(type, CrudRepository.class.getDeclaredMethod("delete", Object.class));
 		assertSaveMethodOn(type, CrudRepository.class.getDeclaredMethod("save", Object.class));
-		assertFindAllMethodOn(type, CrudRepository.class.getDeclaredMethod("findAll"));
+		assertFindAllMethodOn(type, ReadOnlyRepository.class.getDeclaredMethod("findAll"));
 	}
 
 	@Test // DATACMNS-464