Repository

Repository의 역할 에 대해선 이전에 알아보았다.
또 우리는 프로젝트를 생성할때 Spring Data JPA Dependencies 를 추가하였다.
이를 활용하여 간단한 crud 를 만들어보자.

Spring Data JPA 란 ?

Spring Data JPA 는 JPA 를 한단계 더 추상화시킨 Repository 인터페이스를 제공하며 hibername 구현체를 사용한다.

Spring Data JPA 사용법

package com.hello.hello.repository;

import com.hello.hello.domain.entity.Member;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface MemberJpaRepository extends JpaRepository<Member,Long> {
}

MemberJpaRepository 라는 이름의 interface 를 만들고 JpaRepository 를 상속받는다.
extends JpaRepository<Entiry , PK Type>

JpaRepository

/*
 * Copyright 2008-2023 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.jpa.repository;

import java.util.List;

import javax.persistence.EntityManager;

import org.springframework.data.domain.Example;
import org.springframework.data.domain.Sort;
import org.springframework.data.repository.NoRepositoryBean;
import org.springframework.data.repository.PagingAndSortingRepository;
import org.springframework.data.repository.query.QueryByExampleExecutor;

/**
 * JPA specific extension of {@link org.springframework.data.repository.Repository}.
 *
 * @author Oliver Gierke
 * @author Christoph Strobl
 * @author Mark Paluch
 * @author Sander Krabbenborg
 * @author Jesse Wouters
 * @author Greg Turnquist
 */
@NoRepositoryBean
public interface JpaRepository<T, ID> extends PagingAndSortingRepository<T, ID>, QueryByExampleExecutor<T> {

	/*
	 * (non-Javadoc)
	 * @see org.springframework.data.repository.CrudRepository#findAll()
	 */
	@Override
	List<T> findAll();

	/*
	 * (non-Javadoc)
	 * @see org.springframework.data.repository.PagingAndSortingRepository#findAll(org.springframework.data.domain.Sort)
	 */
	@Override
	List<T> findAll(Sort sort);

	/*
	 * (non-Javadoc)
	 * @see org.springframework.data.repository.CrudRepository#findAll(java.lang.Iterable)
	 */
	@Override
	List<T> findAllById(Iterable<ID> ids);

	/*
	 * (non-Javadoc)
	 * @see org.springframework.data.repository.CrudRepository#save(java.lang.Iterable)
	 */
	@Override
	<S extends T> List<S> saveAll(Iterable<S> entities);

	/**
	 * Flushes all pending changes to the database.
	 */
	void flush();

	/**
	 * Saves an entity and flushes changes instantly.
	 *
	 * @param entity entity to be saved. Must not be {@literal null}.
	 * @return the saved entity
	 */
	<S extends T> S saveAndFlush(S entity);

	/**
	 * Saves all entities and flushes changes instantly.
	 *
	 * @param entities entities to be saved. Must not be {@literal null}.
	 * @return the saved entities
	 * @since 2.5
	 */
	<S extends T> List<S> saveAllAndFlush(Iterable<S> entities);

	/**
	 * Deletes the given entities in a batch which means it will create a single query. This kind of operation leaves JPAs
	 * first level cache and the database out of sync. Consider flushing the {@link EntityManager} before calling this
	 * method.
	 *
	 * @param entities entities to be deleted. Must not be {@literal null}.
	 * @deprecated Use {@link #deleteAllInBatch(Iterable)} instead.
	 */
	@Deprecated
	default void deleteInBatch(Iterable<T> entities) {
		deleteAllInBatch(entities);
	}

	/**
	 * Deletes the given entities in a batch which means it will create a single query. This kind of operation leaves JPAs
	 * first level cache and the database out of sync. Consider flushing the {@link EntityManager} before calling this
	 * method.
	 *
	 * @param entities entities to be deleted. Must not be {@literal null}.
	 * @since 2.5
	 */
	void deleteAllInBatch(Iterable<T> entities);

	/**
	 * Deletes the entities identified by the given ids using a single query. This kind of operation leaves JPAs first
	 * level cache and the database out of sync. Consider flushing the {@link EntityManager} before calling this method.
	 *
	 * @param ids the ids of the entities to be deleted. Must not be {@literal null}.
	 * @since 2.5
	 */
	void deleteAllByIdInBatch(Iterable<ID> ids);

	/**
	 * Deletes all entities in a batch call.
	 */
	void deleteAllInBatch();

	/**
	 * Returns a reference to the entity with the given identifier. Depending on how the JPA persistence provider is
	 * implemented this is very likely to always return an instance and throw an
	 * {@link javax.persistence.EntityNotFoundException} on first access. Some of them will reject invalid identifiers
	 * immediately.
	 *
	 * @param id must not be {@literal null}.
	 * @return a reference to the entity with the given identifier.
	 * @see EntityManager#getReference(Class, Object) for details on when an exception is thrown.
	 * @deprecated use {@link JpaRepository#getReferenceById(ID)} instead.
	 */
	@Deprecated
	T getOne(ID id);

	/**
	 * Returns a reference to the entity with the given identifier. Depending on how the JPA persistence provider is
	 * implemented this is very likely to always return an instance and throw an
	 * {@link javax.persistence.EntityNotFoundException} on first access. Some of them will reject invalid identifiers
	 * immediately.
	 *
	 * @param id must not be {@literal null}.
	 * @return a reference to the entity with the given identifier.
	 * @see EntityManager#getReference(Class, Object) for details on when an exception is thrown.
	 * @deprecated use {@link JpaRepository#getReferenceById(ID)} instead.
	 * @since 2.5
	 */
	@Deprecated
	T getById(ID id);

	/**
	 * Returns a reference to the entity with the given identifier. Depending on how the JPA persistence provider is
	 * implemented this is very likely to always return an instance and throw an
	 * {@link javax.persistence.EntityNotFoundException} on first access. Some of them will reject invalid identifiers
	 * immediately.
	 *
	 * @param id must not be {@literal null}.
	 * @return a reference to the entity with the given identifier.
	 * @see EntityManager#getReference(Class, Object) for details on when an exception is thrown.
	 * @since 2.7
	 */
	T getReferenceById(ID id);

	/*
	 * (non-Javadoc)
	 * @see org.springframework.data.repository.query.QueryByExampleExecutor#findAll(org.springframework.data.domain.Example)
	 */
	@Override
	<S extends T> List<S> findAll(Example<S> example);

	/*
	 * (non-Javadoc)
	 * @see org.springframework.data.repository.query.QueryByExampleExecutor#findAll(org.springframework.data.domain.Example, org.springframework.data.domain.Sort)
	 */
	@Override
	<S extends T> List<S> findAll(Example<S> example, Sort sort);
}

JpaRepository 를 상속받으면 위의 메서드 들을 사용할수 있다.
어떤 타입의 Entity 가 들어올지 모르므로 제네릭을 사용한것을 볼수있다.