JPA(ORM) vs. MyBatis(SQL Mapper)

JDBC

Java DataBase Connectivity

• Java에서 DB를 연결하고, DB의 데이터를 가져오기 위해 사용하는 API
• Java & DB
• Java - JDBC API - JDBC Driver - DBMS
• JDBC API는 JDK에 포함되어있음
  • java.sql , javax.sql package
• Java application에서 DBMS의 종류에 상관없이 JDBC API를 사용해 작업
  • DBMS는 JDBC API를 구현한 드라이버를 제공
• Class & Interface
  • DriverManager : loads JDBC Driver
  • Connection : Interface to connect DB
  • Statement / PreparedStatement / CallableStatement : tranmit SQL
    • Statement : no argument
    • PreparedStatement : takes arguments
    • CallableStatement : used for PL/SQL(Procedural language extionsion to SQL)
  • ResultSet : SQL statement의 result를 저장하는 객체
• Operating Procedure
  • load JDBC Driver
  • Create Connecntion object
  • Create Statement object
  • Execute SQL statement
  • Take data from ResultSet object
    • checks if next data exists by ResultSet.next()
    • by column name or index(starts from 1)
  • Deconstruct ResultSet, Statement, Connection

SQL Mapper & ORM

• JDBC is provided by Java for Data Persistence, but quite annoying
• SQL Mapper & ORM is Persistence Framework that help developer using JDBC
• SQL Mapper
  • 객체와 SQL을 매핑하여 데이터를 객체화 하는 기술
    • 객체와 테이블 간의 관계를 매핑하는 것이 아닌 SQL문을 직접 작성하고 쿼리 수행 결과를 어떠한 객체에 매핑할지 바인딩 하는 방법
  • +) 세부적인 SQL 변경시 편리함
  • • ) DBMS에 종속적, SQL 의존적, 패러다임의 불일치
• ORM(Object-Relational Mapping)
  • 객체와 DB Table을 매핑하여 데이터를 객체화 하는 기술
    • SQL문이 아닌 RDB의 데이터 자체와 매핑
    • 객체와 DB를 각자 설계한다.
  • +) DBMS에 종속적이지 않음, 객체 지향적 biz logic
  • • ) learning curve, SQL statement might be efficient for complex logic

MyBatis(SQL Mapper)

• MyBatis : Object mapping technique
• Write Query & map result of query with object
• can divide query to xml

Problem of SQL Mapper

• SQL dependent
  • All the SQL statements change for modification of functionalities
• 패러다임의 불일치
  • OOP provides various policies that can control complexity of system, like Abstraction, Polymorphism, Inheritence, Encapsulation, …
  • Relational-DB doesn;t have such concepts
  • We spend time & codes solving such problems
  • JPA provides inheritence, relationship, object graph traversing, compare

JPA(ORM)

• Java Persistence API : Standard of Java ORM tech.
  • Collections of Interfaces
  • Hibernate, EclipseLink, DataNucleus, … implements JPA
• Operating Procedure
  • Operates between Application & JDBC
    • dev. calls JPA → JPA calls SQL by JDBC API
    • dev. is not using JDBC API directly
  • Save : jpa.persist(DATA)
    • dev. transfer Object to JPA
    • JPA
      • analyze Object Entity
      • create INSERT SQL
      • transfer SQL to DB through JDBC API
  • Read : jpa.find(id)
    • dev. tranfer Primary Key to JPA
    • JPA
      • create SELECT SQL based on Entity Mapping
      • transfer SQL to DB through JDBC API
      • get result from DB
      • map result(ResultSet) to Object
• Why JPA ?
  • migrate from SQL-centered dev. to Obejct-centered dev.
    • Problem of SQL-centered dev.
      • repeating boaring CRUD(codes)
      • Paradigm imcompetance between OOP and RDB
      • Difference between Object & RDB
  • Productivity
    • Using JPA is making data managing process simple
    • Simple CRUD
      • CREATE : jpa.persist(DATA)
      • READ : jpa.find(PK)
      • UPDATE : READ → MODIFY → CREATE
      • DELETE : jpa.remove(DATA)
    • Maintanace
      • All the SQL must be modified when field has been modified
      • JPA : All dev. have to do is to modifing field
        • SQL will be managed by JPA
    • Performance Optimization of JPA
      • buffered writing
      • caching while reading