Mybatis

1. Mybatis 介绍

   MyBatis是支持普通 SQL 查询，存储过程和高级映射的优秀持久 层框架。MyBatis 消除了几乎所有的 JDBC 代码和参数的手工设置以 及对结果集的检索封装。MyBatis 可以使用简单的 XML 或注解用于 配置和原始映射，将接口和 Java 的 POJO（Plain Old Java Objects，普 通的 Java 对象）映射成数据库中的记录.

2. 常见的ORM框架

   JDBC‐dbUtils‐ MyBatis‐ Hibernate 
   

3. mybatis 快速入门

maven依赖

<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.3.0</version>
</dependency>
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.36</version>
</dependency>

建库建表

CREATE TABLE emp
(
    empno INT(10) UNSIGNED PRIMARY KEY NOT NULL AUTO_INCREMENT,
    ename VARCHAR(15),
    job VARCHAR(10),
    mgr INT(10) UNSIGNED,
    hiredate DATE,
    sal DECIMAL(7,2),
    comm DECIMAL(7,2),
    deptno INT(10) UNSIGNED,
    hiredateb DATETIME,
    mgrb INT(11),
    phone VARCHAR(255),
    CONSTRAINT emp_ibfk_1 FOREIGN KEY (deptno) REFERENCES dept (deptno)
);
 
CREATE INDEX deptno ON emp (deptno);   
INSERT INTO scott.emp (ename, job, mgr, hiredate, sal, comm, deptno, hiredateb, mgrb, phone) VALUES ('JONES', 'MANAGER', 7839, '1981-04-02', 2975.00, null, 20, null, null, null);
INSERT INTO scott.emp (ename, job, mgr, hiredate, sal, comm, deptno, hiredateb, mgrb, phone) VALUES ('MARTIN', 'SALESMAN', 7698, '1981-09-28', 1250.00, 1400.00, 30, null, null, null);
INSERT INTO scott.emp (ename, job, mgr, hiredate, sal, comm, deptno, hiredateb, mgrb, phone) VALUES ('BLAKE', 'MANAGER', 7839, '1981-05-01', 2850.00, null, 30, null, null, null);
INSERT INTO scott.emp (ename, job, mgr, hiredate, sal, comm, deptno, hiredateb, mgrb, phone) VALUES ('CLARK', 'MANAGER', 7839, '1981-06-09', 2450.00, null, 10, null, null, null);
INSERT INTO scott.emp (ename, job, mgr, hiredate, sal, comm, deptno, hiredateb, mgrb, phone) VALUES ('SCOTT', 'ANALYST', 7566, '1987-07-13', 3000.00, null, 20, null, null, null);
INSERT INTO scott.emp (ename, job, mgr, hiredate, sal, comm, deptno, hiredateb, mgrb, phone) VALUES ('KING', 'PRESIDENT', null, '1981-11-17', 5000.00, null, 10, null, null, null);
INSERT INTO scott.emp (ename, job, mgr, hiredate, sal, comm, deptno, hiredateb, mgrb, phone) VALUES ('TURNER', 'SALESMAN', 7698, '1981-09-08', 1500.00, 0.00, 30, null, null, null);
INSERT INTO scott.emp (ename, job, mgr, hiredate, sal, comm, deptno, hiredateb, mgrb, phone) VALUES ('ADAMS', 'CLERK', 7788, '1987-07-13', 1100.00, null, 20, null, null, null);
INSERT INTO scott.emp (ename, job, mgr, hiredate, sal, comm, deptno, hiredateb, mgrb, phone) VALUES ('JAMES', 'CLERK', 7698, '1981-12-03', 950.00, null, 30, null, null, null);
INSERT INTO scott.emp (ename, job, mgr, hiredate, sal, comm, deptno, hiredateb, mgrb, phone) VALUES ('FORD', 'ANALYST', 7566, '1981-12-03', 3000.00, null, 20, null, null, null);

添加配置文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <properties resource="jdbc.properties"></properties>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql:///scott"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="*/*/bean/EmpMapper.xml"></mapper>
    </mappers>
</configuration>

创建实体类
public class Emp implements Serializable {
    private Integer empno;
    private String ename;
    private String job;
    private  Double sal;
    private Dept dept;
}

创建mapper文件
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="*.*.EmpMapper">
</mapper>
注册mapper文件
<mappers>
        <mapper resource="*/*/bean/EmpMapper.xml"></mapper>
</mappers>

执行定义的select语句
String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        List<Emp> emps = sqlSession.selectList("cn.bdqn.bean.EmpMapper.selectEmp");
        for (Emp emp : emps) {
            System.out.println(emp);
        }

操作 users 表的 CRUD
XML的实现
注解的实现

几个可以优化的地方
连接数据库的配置单独放在一个 properties 文件中

driver=com.mysql.jdbc.Driver
url=jdbc:mysql:///scott
username=root
password=root
 
<properties resource="jdbc.properties"></properties>
 可以在 src 下加入 log4j 的配置文件,打印日志信息 
log4j.rootLogger=DEBUG, Console
#Console
log4j.appender.Console=org.apache.log4j.ConsoleAppender
log4j.appender.Console.layout=org.apache.log4j.PatternLayout
log4j.appender.Console.layout.ConversionPattern=%d [%t] %‐5p [%c] ‐ %m%n
log4j.logger.java.sql.ResultSet=INFO
log4j.logger.org.apache=INFO
log4j.logger.java.sql.Connection=DEBUG
log4j.logger.java.sql.Statement=DEBUG
log4j.logger.java.sql.PreparedStatement=DEBUG

<settings>
       <setting name="logImpl" value="LOG4J" />
</settings>

SqlSessionFacotryUtils

private static final ThreadLocal<SqlSession> threadLocal = new ThreadLocal<SqlSession>();
    private static SqlSessionFactory sessionFactory;
    static String CONFIG_FILE_LOCATION = "mybatis-config.xml";
    static InputStream inputStream;
    private static Properties properties;
 
    static {
        try {
            properties= new Properties();
            properties.load(MyBatisSessionFactory.class.getClassLoader().getResourceAsStream("jdbc.properties"));
inputStream = Resources.getResourceAsStream(CONFIG_FILE_LOCATION);
            sessionFactory = new SqlSessionFactoryBuilder().build(inputStream,properties);
        } catch (Exception e) {
            System.err.println("%%%% Error Creating SessionFactory %%%%");
            e.printStackTrace();
        }
    }
 
    private MyBatisSessionFactory() {
    }
 
 
    public static SqlSession getSession() {
        System.out.println("1111111111111");
        SqlSession session = (SqlSession) threadLocal.get();
 
        if (session == null) {
            if (sessionFactory == null) {
                rebuildSessionFactory();
            }
             session = (sessionFactory != null) ? sessionFactory.openSession()
                    : null;
            threadLocal.set(session);
        }
 
        return session;
    }
 
 
    public static void rebuildSessionFactory() {
        try {
            inputStream = Resources.getResourceAsStream(CONFIG_FILE_LOCATION);
            sessionFactory = new SqlSessionFactoryBuilder().build(inputStream,properties);
         } catch (Exception e) {
            System.err.println("%%%% Error Creating SessionFactory %%%%");
            e.printStackTrace();
        }
    }
 
 
    public static void closeSession() {
        SqlSession session = (SqlSession) threadLocal.get();
        threadLocal.set(null);
 
        if (session != null) {
            session.close();
        }
    }
 
   
    public static SqlSessionFactory getSessionFactory() {
        return sessionFactory;
    }
 
   
    public static void setConfigFile(String configFile) {
        MyBatisSessionFactory.CONFIG_FILE_LOCATION = configFile;
        sessionFactory = null;
    }

解决字段名与实体类属性名不相同的冲突
准备表和数据
定义实体类
查询
as
ResultMap
实现关联表查询
需求
员工和员工详细信息
一对一
Association 用于一对一的关联查询
Property :对象属性的名称
Javatype:对象属性的类型
Column:所对应的外键字段名称
Select:使用另一个查询封装结果
嵌套结果

嵌套查询

一对多关联
Collection : 一对多关联查询
ofType:指定集合中元素对象的类型

嵌套结果

嵌套查询

动态 SQL 与模糊查询
If
Choose(when otherwise)
Trim(where,set)
Foreach
调用存储过程

Mybatis 缓存
一级缓存: 基于 PerpetualCache 的 HashMap 本地缓存，其存储作用域为 Session，当 Session flush 或 close 之后，该 Session 中的所有 Cache 就将清空。
二级缓存与一级缓存其机制相同，默认也是采用 PerpetualCache，HashMap 存储，不同在于 其存储作用域为 Mapper(Namespace)，并且可自定义存储源，如 Ehcache
对于缓存数据更新机制，当某一个作用域(一级缓存 Session/二级缓存 Namespaces)的进行了 C/U/D 操作后，默认该作用域下所有 select 中的缓存将被 clear。
spring 集成 mybatis
maven依赖
实体类
mapper文件
数据表和数据
数据库
Spring配置
关联properties文件
数据源
sqlSessionFatory
加载mapper文件
事务管理
测试