MyBatis 总结

Posted 2020-07-19

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1. mybatis 快速入门:
1). 添加 jar 包
   mybatis-3.1.1.jar
   mysql-connector-java-5.1.7-bin.jar
2). 建库建表

create database mybatis;
   use mybatis;
   CREATE TABLE users(id INT PRIMARY KEY AUTO_INCREMENT, NAME VARCHAR(20), age INT);
   INSERT INTO users(NAME, age) VALUES(‘Tom‘, 12);
   INSERT INTO users(NAME, age) VALUES(‘Jack‘, 11);

3). 添加 Mybatis 的配置文件 conf.xml

<?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>
    <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://localhost:3306/mybatis" />
       <property name="username" value="root" />
       <property name="password" value="root" />
      </dataSource>
     </environment>
    </environments>
   </configuration>

4). 定义表所对应的实体类

public class User {
    private int id;
    private String name;
    private int age;
    //get,set 方法
   }

5). 定义操作 users 表的 sql 映射文件 userMapper.xml

 <?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=" com.irvin.mybatis_test.test1.userMapper">
    <select id="getUser" parameterType="int"
    resultType="com.irvin.mybatis_test.test1.User">
     select * from users where id=#{id}
    </select>
   </mapper>

6). 在 conf.xml 文件中注册 userMapper.xml 文件

<mappers>
    <mapper resource="com/irvin/mybatis_test/test1/userMapper.xml"/>
   </mappers>

7). 编写测试代码：执行定义的 select 语句

 public class Test {
    public static void main(String[] args) throws IOException {
     String resource = "conf.xml";
     //加载 mybatis 的配置文件（它也加载关联的映射文件）
     Reader reader = Resources.getResourceAsReader(resource);
     //构建 sqlSession 的工厂
     SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);
     //创建能执行映射文件中 sql 的 sqlSession
     SqlSession session = sessionFactory.openSession();
     //映射 sql 的标识字符串
     String statement = "com.atguigu.mybatis.bean.userMapper"+".selectUser";
     //执行查询返回一个唯一user 对象的sql
     User user = session.selectOne(statement, 1);
     System.out.println(user);
    }
   }

2. 一对一关联：

<select id="getClass" parameterType="int" resultMap="ClassResultMap">
  select * from class c, teacher t where c.teacher_id=t.t_id and c.c_id=#{id}
</select>

<resultMap type="_Classes" id="ClassResultMap">
  <id property="id" column="c_id"/>
  <result property="name" column="c_name"/>
  <association property="teacher" column="teacher_id" javaType="_Teacher">
   <id property="id" column="t_id"/>
   <result property="name" column="t_name"/>
  </association>
</resultMap>

<select id="getClass2" parameterType="int" resultMap="ClassResultMap2">
  select * from class where c_id=#{id}
</select>

<resultMap type="_Classes" id="ClassResultMap2">
  <id property="id" column="c_id"/>
  <result property="name" column="c_name"/>
  <association property="teacher" column="teacher_id" javaType="_Teacher"
   select="getTeacher">
  </association>
</resultMap>

<select id="getTeacher" parameterType="int" resultType="_Teacher">
  SELECT t_id id, t_name name FROM teacher WHERE t_id=#{id}
</select>

3. 一对多关联：

<select id="getClass3" parameterType="int" resultMap="ClassResultMap3">
  select * from class c, teacher t,student s where c.teacher_id=t.t_id and c.C_id=s.class_id and c.c_id=#{id}
</select>

<resultMap type="_Classes" id="ClassResultMap3">
  <id property="id" column="c_id"/>
  <result property="name" column="c_name"/>
  <association property="teacher" column="teacher_id" javaType="_Teacher">
   <id property="id" column="t_id"/>
   <result property="name" column="t_name"/>
  </association>
  
  <collection property="students" ofType="_Student">
   <id property="id" column="s_id"/>
   <result property="name" column="s_name"/>
  </collection>
</resultMap>


<select id="getClass4" parameterType="int" resultMap="ClassResultMap4">
  select * from class where c_id=#{id}
</select>

<select id="getTeacher2" parameterType="int" resultType="_Teacher">
SELECT t_id id, t_name name FROM teacher WHERE t_id=#{id}
</select>

<select id="getStudent" parameterType="int" resultType="_Student">
SELECT s_id id, s_name name FROM student WHERE class_id=#{id}
</select>

4. 动态 SQL 与模糊查询
<?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="com.irvin.day03_mybatis.test6.userMapper">
  <select id="getUser" parameterType="com.irvin.day03_mybatis.test6.ConditionUser"
   resultType="com.irvin.day03_mybatis.test6.User">
   select * from d_user where age>=#{minAge} and age<=#{maxAge}
   <if test=‘name!="%null%"‘>and name like #{name}</if>
  </select>
</mapper>

5. 调用存储过程
<mapper namespace="com.atguigu.day03_mybatis.test7.userMapper">
  <select id="getCount" resultType="java.util.Map" statementType="CALLABLE">
   {call
    ges_user_count(#{sex_id,mode=IN,jdbcType=INTEGER},#{result,mode=OUT,jdbcType=INTEGER})
   }
  </select>
</mapper>

6. 缓存机制 :
1). 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。

  /*
   * 一级缓存: 也就Session 级的缓存(默认开启)
   */
  @Test
  public void testCache1() {
   SqlSession session = MybatisUtils.getSession();
   String statement = "com.atguigu.mybatis.test8.userMapper.getUser";
   User user = session.selectOne(statement, 1);
   System.out.println(user);

   /*
    * 一级缓存默认就会被使用
    */

   /*
    user = session.selectOne(statement, 1);
    System.out.println(user);
   */

   /*
    1. 必须是同一个Session,如果session 对象已经close()过了就不可能用了
    */

   /*
    session = MybatisUtils.getSession();
    user = session.selectOne(statement, 1);
    System.out.println(user);
   */

   /*
    2. 查询条件是一样的
   */

   /*
    user = session.selectOne(statement, 2);
    System.out.println(user);
   */

   /*
    3. 没有执行过session.clearCache()清理缓存
   */

   /*
    session.clearCache();
    user = session.selectOne(statement, 2);
    System.out.println(user);
   */

   /*
    4. 没有执行过增删改的操作(这些操作都会清理缓存)
   */

   /*
    session.update("com.atguigu.mybatis.test8.userMapper.updateUser",
    new User(2, "user", 23));
    user = session.selectOne(statement, 2);
    System.out.println(user);
   */
  }

2). 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。
3). 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。

  添加一个<cache>在userMapper.xml 中
   <mapper namespace="com.atguigu.mybatis.test8.userMapper">
   <cache/>

7. spring 集成 mybatis

1). 添加Jar 包
  [mybatis]
   mybatis-3.2.0.jar
   mybatis-spring-1.1.1.jar
   log4j-1.2.17.jar

  [spring]
   spring-aop-3.2.0.RELEASE.jar
   spring-beans-3.2.0.RELEASE.jar
   spring-context-3.2.0.RELEASE.jar
   spring-core-3.2.0.RELEASE.jar
   spring-expression-3.2.0.RELEASE.jar
   spring-jdbc-3.2.0.RELEASE.jar
   spring-test-3.2.4.RELEASE.jar
   spring-tx-3.2.0.RELEASE.jar
   aopalliance-1.0.jar
   cglib-nodep-2.2.3.jar
   commons-logging-1.1.1.jar

[MYSQL 驱动包]
mysql-connector-java-5.0.4-bin.jar

2). 数据库表
   CREATE TABLE s_user(
   user_id INT AUTO_INCREMENT PRIMARY KEY,
   user_name VARCHAR(30),
   user_birthday DATE,
   user_salary DOUBLE
   )

3). 实体类: User
   public class User {
    private int id;
    private String name;
    private Date birthday;
    private double salary;
    //set,get 方法
   }

4). DAO 接口: UserMapper (XXXMapper)
   public interface UserMapper {
    void save(User user);
    void update(User user);
    void delete(int id);
    User findById(int id);
    List<User> findAll();
   }

5). SQL 映射文件: userMapper.xml
   <?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="com.atguigu.mybatis.test9.UserMapper">
    <resultMap type="User" id="userResult">
     <result column="user_id" property="id"/>
     <result column="user_name" property="name"/>
     <result column="user_birthday" property="birthday"/>
     <result column="user_salary" property="salary"/>
    </resultMap>

<insert id="save" keyColumn="user_id" keyProperty="id" useGeneratedKeys="true">
     insert into s_user(user_name,user_birthday,user_salary)
     values(#{name},#{birthday},#{salary})
    </insert>

    <update id="update">
     update s_user
     set user_name = #{name},
     user_birthday = #{birthday},
     user_salary = #{salary}
     where user_id = #{id}
    </update>

    <delete id="delete">
     delete from s_user
     where user_id = #{id}
    </delete>

    <select id="findById" resultMap="userResult">
     select * from s_user
     where user_id = #{id}
    </select>

    <select id="findAll" resultMap="userResult">
     select *
     from s_user
    </select>
   </mapper>

6). spring 的配置文件: beans.xml
   <?xml version="1.0" encoding="UTF-8"?>
   <beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:p="http://www.springframework.org/schema/p"
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xsi:schemaLocation="
     http://www.springframework.org/schema/beans
     http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
     http://www.springframework.org/schema/context
     http://www.springframework.org/schema/context/spring-context-3.2.xsd
     http://www.springframework.org/schema/tx
     http://www.springframework.org/schema/tx/spring-tx-3.2.xsd">

    
    <bean id="dataSource"
     class="org.springframework.jdbc.datasource.DriverManagerDataSource">
     <property name="driverClassName" value="com.mysql.jdbc.Driver"/>
     <property name="url" value="jdbc:mysql://localhost:3306/mybatis"/>
     <property name="username" value="root"/>
     <property name="password" value="root"/>
    </bean>

<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
     <property name="dataSource" ref="dataSource"/>
     <property name="typeAliasesPackage" value="com.irvin.spring_mybatis2.domain"/>
    </bean>

<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
     <property name="basePackage" value="com.irvin.spring_mybatis2.mapper"/>
     <property name="sqlSessionFactory" ref="sqlSessionFactory"/>
    </bean>

<bean id="txManager"
     class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
     <property name="dataSource" ref="dataSource"/>
    </bean>

<tx:annotation-driven transaction-manager="txManager" />
   </beans>

7). mybatis 的配置文件: mybatis-config.xml
   <?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>
    
    
    
    
    
   </configuration>

8). 测试
   @RunWith(SpringJUnit4ClassRunner.class) //使用Springtest框架

   @ContextConfiguration("/beans.xml") //加载配置
   public class SMTest {
    @Autowired //注入
    private UserMapper userMapper;

    @Test
    public void save() {
     User user = new User();
     user.setBirthday(new Date());
     user.setName("marry");
     user.setSalary(300);
     userMapper.save(user);
     System.out.println(user.getId());
    }

    @Test
    public void update() {
     User user = userMapper.findById(2);
     user.setSalary(2000);
     userMapper.update(user);
    }

    @Test
    public void delete() {
     userMapper.delete(3);
    }

    @Test
    public void findById() {
     User user = userMapper.findById(1);
     System.out.println(user);
    }

    @Test
    public void findAll() {
     List<User> users = userMapper.findAll();
     System.out.println(users);
    }
   }

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