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mybatis初探（一）

分类: 文章 • 2022-10-06 22:59:15

一、什么是mybatis

        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。 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.

        1）MyBATIS 目前提供了三种语言实现的版本，包括：Java、.NET以及Ruby。（我主要学习java，就讲java的使用）
        2）它提供的持久层框架包括SQL Maps和Data Access Objects（DAO）。
        3）mybatis与hibernate的对比？

              mybatis提供一种“半自动化”的ORM实现。 这里的“半自动化”，是相对Hibernate等提供了全面的数据库封装机制的“全自动化”ORM实现而言，“全自动”ORM实现了POJO和数据库表之间的映射，以及 SQL 的自动生成和执行。 而mybatis的着力点，则在于POJO与SQL之间的映射关系。

二、mybatis架构图

       

mybatis初探（一）

        执行流程：

        1、mapper-config.xml配合好全局属性，经数据源引入映射文件（mapper.xml）

        2、通过SqlSessionFactory工厂bean获取sqlsession会话对象实例

        3、sqlsession对象操作CRUD

        4、执行器将statement中的数据库语句解析执行相关的数据库操作

 

三、mybatis入门实例

      3.1、引入依赖

<dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.12</version>
      <scope>test</scope>
    </dependency>
    <!--引入spring的相关依赖-->
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-context</artifactId>
      <version>5.1.5.RELEASE</version>
    </dependency>

    <dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.0</version>
  </dependency>

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-test</artifactId>
      <version> 5.1.5.RELEASE  </version>
      <scope>provided</scope>
    </dependency>

    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>8.0.15</version>
    </dependency>

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-jdbc</artifactId>
      <version>5.1.5.RELEASE</version>
    </dependency>

       3.2、配置mybatis-config.xml全局文件

<?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>
        <!--各个标签的顺序不能变-->
        <properties resource="application.properties"></properties>

        <!--延时加载： -->
        <!--1、直接加载：执行完对主加载对象的select语句，马上执行对关联对象的select查询。-->
        <!--2、侵入式延迟（按需加载）：执行对主加载对象的查询时，不会执行对关联对象的查询。但当要访问主加载对象的详情时，就会马上执行关联对象的select查询。-->
        <!--3、深度延迟：执行对主加载对象的查询时，不会执行对关联对象的查询。访问主加载对象的详情时也不会执行关联对象的select查询。只有当真正访问关联对象的详情时，才会执行对关联对象的select查询。-->
        <settings>
            <setting name="lazyLoadingEnabled" value="true"/>
            <setting name="aggressiveLazyLoading" value="false"/>
        </settings>
     
        <environments default="demoMyBatis">
            <environment id="demoMyBatis">
                <transactionManager type="JDBC"></transactionManager>
                <dataSource type="POOLED">
                    <property name="driver" value="${jdbc.driverClassName}"></property>
                    <property name="url" value="${jdbc.url}"></property>
                    <property name="username" value="${jdbc.username}"></property>
                    <property name="password" value="${jdbc.password}"></property>
                </dataSource>
            </environment>
        </environments>

        <mappers>
            <mapper resource="mapper/studentMapper.xml"/>
            <mapper resource="mapper/UserMapper.xml"/>
            <mapper resource="mapper/CountryMapper.xml"/>
            <mapper resource="mapper/MinisterMapper.xml"/>
            <mapper resource="mapper/NewsMapper.xml"/>
        </mappers>

</configuration>

        3.3、创建数据库表及其实例对象

           1、创建student数据库表

DROP TABLE IF EXISTS `student`;

CREATE TABLE `student` (
  `id` int(2) NOT NULL AUTO_INCREMENT,
  `user_name` varchar(15) COLLATE utf8_bin NOT NULL,
  `password` varchar(15) COLLATE utf8_bin NOT NULL,
  `local_address` varchar(25) COLLATE utf8_bin NOT NULL,
  `sex` varchar(4) COLLATE utf8_bin NOT NULL,
  `age` int(2) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8 COLLATE=utf8_bin;

/*Data for the table `student` */

insert  into `student`(`id`,`user_name`,`password`,`local_address`,`sex`,`age`) values 
(1,'李薇','234155','湖南常德','女',34),
(2,'李四','123456','深圳市龙华区','男',27),
(3,'mark','123456','美国华盛顿','男',47);

             2、创建student实体

    private int id;

    private String username;

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                ", localAddress='" + localAddress + '\'' +
                ", sex='" + sex + '\'' +
                ", age=" + age +
                '}';
    }

    private String password;

    private String localAddress;

    private String sex;

    private int age;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getLocalAddress() {
        return localAddress;
    }

    public void setLocalAddress(String localAddress) {
        this.localAddress = localAddress;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

           3.4、配置StudentMapper.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.achuan.demo.dao.StudentDao">

    <select id="selectById" parameterType="int" resultMap="student">
           select * from student where id = #{id}
    </select>

    <select id="selectAll" resultMap="student">
           select * from student;
    </select>

    <select id="selectBySex" parameterType="string" resultMap="student">
           select * from student where sex = #{sex};
    </select>

    <!--useGeneratedKeys:开启主键回写
        keyColumn：指定数据库的主键
        keyProperty：主键对应的pojo属性名-->
    <insert id="insert" parameterType="com.achuan.demo.entity.Student" useGeneratedKeys="true" keyColumn="id" keyProperty="id">
           insert into student(
           id,
           user_name,
           password,
           sex,
           local_address,
           age
           )values (
           null,
           #{username},
           #{password},
           #{sex},
           #{localAddress},
           #{age}
           );
    </insert>

    <update id="update" parameterType="com.achuan.demo.entity.Student">
        update student
        <trim prefix="set" suffixOverrides=",">
            <if test="username!=null">user_name = #{username},</if>
            <if test="password!=null">password = #{password},</if>
            <if test="sex!=null">sex = #{sex},</if>
            <if test="localAddress!=null">local_address = #{localAddress},</if>
            <if test="age!=null">age = #{age}</if>
        </trim>
        where id = #{id};
    </update>

    <delete id="deleteById" parameterType="int">
        delete from student where id = #{id};
    </delete>

    <resultMap id="student" type="com.achuan.demo.entity.Student">
        <!--jdbcType的值必须得大写-->
        <id column="id" jdbcType="INTEGER" property="id"/>
        <result column="user_name" jdbcType="VARCHAR" property="username"/>
        <result column="password" jdbcType="VARCHAR" property="password"/>
        <result column="local_address" jdbcType="VARCHAR" property="localAddress"/>
        <result column="sex" jdbcType="VARCHAR" property="sex"/>
        <result column="age" jdbcType="INTEGER" property="age"/>
    </resultMap>

</mapper>

            3.5、实现StudentDao接口

               1、创建StudentDao接口并定义增删查改数据库操作方法

public interface StudentDao {

    List<Student> selectAll();

    Student selectById(int id);

    List<Student> selectBySex(String sex);

    void insert(Student student);

    void deleteById(int id);

    void update(Student student);

}

              2、StudentDao的实现类StudentDaoImpl


    public SqlSession sqlSession;

    public StudentDaoImpl(SqlSession sqlSession) {
        this.sqlSession = sqlSession;
    }

    @Override
    public List<Student> selectAll() {
        return this.sqlSession.selectList("com.achuan.demo.dao.StudentDao.selectAll");
    }

    @Override
    public Student selectById(int id) {
        return this.sqlSession.selectOne("com.achuan.demo.dao.StudentDao.selectById",id);
    }

    @Override
    public List<Student> selectBySex(String sex) {
        return this.sqlSession.selectList("com.achuan.demo.dao.StudentDao.selectBySex",sex);
    }

    @Override
    public void insert(Student student) {
        this.sqlSession.insert("com.achuan.demo.dao.StudentDao.insert",student);
    }

    @Override
    public void deleteById(int id) {
        this.sqlSession.delete("com.achuan.demo.dao.StudentDao.deleteById",id);
    }

    @Override
    public void update(Student student) {
        this.sqlSession.update("com.achuan.demo.dao.StudentDao.update",student);
    }

           3.6、引入log4j日志

              1、pom.xml中引入log4j相关依赖

<dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-api</artifactId>
      <version>1.7.7</version>
    </dependency>
    <dependency>
      <groupId>log4j</groupId>
      <artifactId>log4j</artifactId>
      <version>1.2.17</version>
    </dependency>
    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-log4j12</artifactId>
      <version>1.7.7</version>
    </dependency>

              2、配置log4j.properties文件

log4j.rootCategory=debug, stdout
log4j.rootLogger=debug, stdout

### stdout ###
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p - %m%n

### set package ###
log4j.logger.org.springframework=info
log4j.logger.org.apache.catalina=info
log4j.logger.org.apache.commons.digester.Digester=info
log4j.logger.org.apache.catalina.startup.TldConfig=info
log4j.logger.chb.test=debug

             3.7、StudentTest测试类进行测试

 StudentDao studentDao;

    SqlSession sqlSession;

    @Before
    public void before() throws IOException {
        //1、读取mybatis全局配置文件并获取文件输入流
        InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
        //2、通过输入流获取sqlsession的代理工厂bean
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        //3、通过代理工厂bean获取sqlSessions
        sqlSession = sqlSessionFactory.openSession();
        //4、将sqlsession加载进userdao实例对象中去
        studentDao = new StudentDaoImpl(sqlSession);
    }

    @Test
    public void test01(){
        Student student = new Student();
        student.setUsername("mark");
        student.setPassword("123456");
        student.setAge(47);
        student.setSex("男");
        student.setLocalAddress("美国华盛顿");
        studentDao.insert(student);
        //执行数据库操作以后将数据提交给数据库
        this.sqlSession.commit();
    }

                运行结果：

          mybatis初探（一）

          3.8、mybatis使用流程总结

                 1)配置mybatis-config.xml 全局的配置文件 (1、数据源，2、外部的mapper)
                 2)创建SqlSessionFactory
                 3)通过SqlSessionFactory创建SqlSession对象

                 4)通过SqlSession操作数据库 CRUD
                 5)调用session.commit()提交事务
                 6)调用session.close()关闭会话

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