====== Spring Data JDBC ======
  * [[https://projects.spring.io/spring-data-jdbc/|Spring Data JDBC]]
  * https://github.com/spring-projects/spring-data-jdbc
  * [[https://spring.io/blog/2018/09/17/introducing-spring-data-jdbc|Introducing Spring Data JDBC]]
  * [[springframework:spring_data_jdbc:querydsl|Spring Data JDBC & QueryDSL]]

===== 가장 큰 특징 =====
  * Entity 가 proxy 객체가 아닌 POJO 이기 때문에, proxy 일 때 발생하는 숨은 동작들이 발생하지 않는다.
  * 이 특징을 잘 활용하면 side effect 없이 다양한 시도를 할 수 있다.

===== JdbcAggregateTemplate =====
  * [[https://docs.spring.io/spring-data/jdbc/docs/current/api/org/springframework/data/jdbc/core/JdbcAggregateTemplate.html|JdbcAggregateTemplate]]
  * SpringDataJdbc 가 내부적으로 사용하는 DB 제어 template
  * 직접 주입 받아서 사용가능하다.

===== EntityCallback =====
  * [[https://docs.spring.io/spring-data/commons/docs/current/api/org/springframework/data/mapping/callback/EntityCallback.html?is-external=true|EntityCallback]] - Spring Data의 EntityCallback
  * [[https://docs.spring.io/spring-data/jdbc/docs/current/api/org/springframework/data/relational/core/mapping/event/BeforeSaveCallback.html|BeforeSaveCallback]] : Entity 저장전 Callback.
  * 각종 ''Before*Callback''

===== AbstractJdbcConfiguration =====
  * [[https://docs.spring.io/spring-data/jdbc/docs/current/api/org/springframework/data/jdbc/repository/config/AbstractJdbcConfiguration.html|AbstractJdbcConfiguration]] 설정 확장.
  * [[https://docs.spring.io/spring-data/jdbc/docs/current/api/org/springframework/data/jdbc/core/convert/JdbcCustomConversions.html|JdbcCustomConversions]] : Custom 객체 -> DB 저장데이터 변환
  * [[https://docs.spring.io/spring-data/commons/docs/current/api/org/springframework/data/convert/WritingConverter.html|@WritingConverter]] : 데이터를 컬럼으로 쓰기할 때 변환
  * [[https://docs.spring.io/spring-data/commons/docs/current/api/org/springframework/data/convert/ReadingConverter.html|@ReadingConverter]] : 데이터를 컬럼에서 객체로 읽을 때 변환

===== Bidirectional Relationship =====
==== internal ====
  * [[https://docs.spring.io/spring-data/commons/docs/current/api/org/springframework/data/annotation/Transient.html|@Transient]] : 해당 피드를 Repository에서 다루지 않는다는 표시.
  * [[https://docs.spring.io/spring-data/commons/docs/current/api/org/springframework/data/annotation/PersistenceConstructor.html|@PersistenceConstructor]] 로 지정된 생성자는 DB에서 데이터 읽어서 객체화 할 때 호출된다.
  * DB 데이터를 읽을 때 생성자에서 ''@Transient'' 필드에 값 주입해서 양방향 관계 흉내가 가능함.

==== external ====
  * 이런 방법 보다는 그냥 [[https://docs.spring.io/spring-data/jdbc/docs/2.2.3/api/org/springframework/data/jdbc/core/mapping/AggregateReference.html|AggregateReference]] 를 사용해 ID 값만 저장하고 ID로 일괄 조회하는 것이 나을 듯. 이것이 SpringDataJDBC의 기본 방침.


===== Caching =====
  * Spring Data JDBC는 Cache를 지원하지 않는다.
  * 필요하다면 [[springframework:cacheabstraction|Spring Cacheh Abstraction]]을 사용한다.

===== Eager Loading =====
  * [[https://docs.spring.io/spring-data/jdbc/docs/2.2.3/api/org/springframework/data/jdbc/core/mapping/AggregateReference.html|AggregateReference]] 로 매핑된 필드를 [[https://docs.spring.io/spring-data/jdbc/docs/2.2.3/api/org/springframework/data/relational/core/mapping/Embedded.html|@Embedded]]로 매핑한 View 객체를 생성하고 일반 SQL 쿼리로 join 을 통해 값을 채우면 된다.
  * [[https://github.com/schauder/talk-beyond/blob/master/src/main/java/de/schauderhaft/beyond/join/MinionView.java|MinionView]] ''Minion''이라는 Entity에 대해 join 데이터를 ''Embed''한 view 클래스.
  * 어차피 조회한 엔티티가 proxy가 아니라서 별다른 side effect 없이 View 객체 사용가능.

<code java>
class MinionView extends Minion {
    MinionView(String name, AggregateReference<Person, Long> evilMaster) {
        super(name, evilMaster);
    }

    @Embedded(onEmpty = Embedded.OnEmpty.USE_EMPTY, prefix = "master_")
    Person master;
}

// join 해서 MinionView에 값을 넣는 Repository 쿼리
@Query("select m.id as id, m.name name, m.number_of_eyes as number_of_eyes, " +
        "p.name as master_name, p.id as master_evil_master " +
        "from minion m join person p on p.id = m.evil_master")
List<MinionView> allMinionViews();
</code>


===== 참조 =====
  * [[https://springone.io/2021/sessions/spring-data-jdbc-beyond-the-obvious|Spring Data JDBC: Beyond the Obvious | SpringOne | Sep 1–2, 2021]]
  * [[https://spring.io/blog/2020/05/20/migrating-to-spring-data-jdbc-2-0|Migrating to Spring Data JDBC 2.0]]
  * [[https://www.baeldung.com/spring-data-jdbc-intro|Introduction to Spring Data JDBC | Baeldung]]
  * [[https://www.infoq.com/presentations/spring-data-jdbc/|The New Kid on the Block: Spring Data JDBC]]
  * [[https://evgeniy-khist.github.io/spring-data-examples/#75e0f07fedd63771fc35ec852a9c937f|Spring Data JPA pitfalls and modern alternatives: Spring Data JDBC and Spring Data R2DBC]]
  * [[https://spring.io/blog/2018/09/24/spring-data-jdbc-references-and-aggregates|Spring Data JDBC, References, and Aggregates]]
  * [[https://spring.io/blog/2021/09/09/spring-data-jdbc-how-to-use-custom-id-generation|Spring Data JDBC - How to use custom ID generation]]
  * [[https://spring.io/blog/2021/09/22/spring-data-jdbc-how-do-i-make-bidirectional-relationships|Spring Data JDBC - How do I make Bidirectional Relationships?]]
  * [[https://spring.io/blog/2021/10/18/spring-data-jdbc-how-do-i-implement-caching|Spring Data JDBC - How do I implement caching?]]
  * [[https://www.youtube.com/watch?v=GOSW911Ox6s|Domain-Driven Design with Relational Databases Using Spring Data JDBC - YouTube]] : Spring Data JDBC에서 내부적으로 자동적으로 처리되는 부분들을 드러내 보여줌.
    * https://github.com/schauder/talk-beyond : 관련 소스
  * [[https://www.youtube.com/watch?v=SJlKBkZ2yAU|Spring Data JDBC: Beyond the Obvious - YouTube]]
  * [[https://luvstudy.tistory.com/174|Spring Data JDBC는 현재 쓸 만할까?]]
    * 2022현재 multiple datasource 지정 안됨
    * [[https://github.com/spring-projects/spring-data-relational/issues/544|Multiple datasources support [DATAJDBC-321] · Issue #544 · spring-projects/spring-data-relational]]
    * [[https://github.com/spring-projects/spring-data-relational/pull/1005|Add jdbcConverterRef to @EnableJdbcRepositories by kota65535 · Pull Request #1005 · spring-projects/spring-data-relational]]
    * [[https://youtube.com/playlist?list=PLbuI9mmWSoUFGL6B_NxB9IoGqyDq-vEen&si=aaNTrHZx_9fswpn6|Spring Dataa JDBC - SpringBoot 3]]