使用MyBatis编写Dao的两种语法

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在MyBatis中，我们有两种Dao的写法，一种叫传统Dao写法，一种叫Mapper代理接口。下面看看如何实现。

1 传统Dao写法

1.1 编写CustomerDao接口

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/**
 * Dao接口
 */
public interface CustomerDao {

    /**
     * 查询所有用户
     */
    public List<Customer> findAll();

    /**
     * 添加
     */
    public void save(Customer customer);

    /**
     * 修改
     */
    public void update(Customer customer);

    /**
     * 查询一个
     */
    public Customer findById(Integer id);

    /**
     * 条件查询
     */
    public List<Customer> findByName(String name);

    /**
     * 删除
     */
    public void delete(Integer id);
}

1.2 编写CustomerDao实现类

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/**
 * Dao实现类
 */
public class CustomerDaoImpl implements CustomerDao{
    @Override
    public List<Customer> findAll() {
        SqlSession sqlSession = null;
        try {
            sqlSession = MyBatisUtils.getSession();
            return sqlSession.selectList("com.yiidian.dao.CustomerDao.findAll");
        } catch (Exception e) {
            e.printStackTrace();
        } finally{
            sqlSession.close();
        }
        return null;
    }

    @Override
    public void save(Customer customer) {
        SqlSession sqlSession = null;
        try {
            sqlSession = MyBatisUtils.getSession();
            sqlSession.insert("com.yiidian.dao.CustomerDao.save", customer);
            sqlSession.commit();
        } catch (Exception e) {
            e.printStackTrace();
            sqlSession.rollback();
        } finally{
            sqlSession.close();
        }
    }

    @Override
    public void update(Customer customer) {
        SqlSession sqlSession = null;
        try {
            sqlSession = MyBatisUtils.getSession();
            sqlSession.update("com.yiidian.dao.CustomerDao.update", customer);
            sqlSession.commit();
        } catch (Exception e) {
            e.printStackTrace();
            sqlSession.rollback();
        } finally{
            sqlSession.close();
        }
    }

    @Override
    public Customer findById(Integer id) {
        SqlSession sqlSession = null;
        try {
            sqlSession = MyBatisUtils.getSession();
            return sqlSession.selectOne("com.yiidian.dao.CustomerDao.findById",id);
        } catch (Exception e) {
            e.printStackTrace();
        } finally{
            sqlSession.close();
        }
        return null;
    }

    @Override
    public List<Customer> findByName(String name) {
        SqlSession sqlSession = null;
        try {
            sqlSession = MyBatisUtils.getSession();
            return sqlSession.selectList("com.yiidian.dao.CustomerDao.findByName",name);
        } catch (Exception e) {
            e.printStackTrace();
        } finally{
            sqlSession.close();
        }
        return null;
    }

    @Override
    public void delete(Integer id) {
        SqlSession sqlSession = null;
        try {
            sqlSession = MyBatisUtils.getSession();
            sqlSession.delete("com.yiidian.dao.CustomerDao.delete", id);
            sqlSession.commit();
        } catch (Exception e) {
            e.printStackTrace();
            sqlSession.rollback();
        } finally{
            sqlSession.close();
        }
    }
}

传统方式的重点在于Dao实现类，在Dao实现类中，手动调用SqlSession提供的方法直接执行映射文件的SQL语句。

1.3 编写CustomerDao.xml映射

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<?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">
<!--
   namespace: 用于指定该映射文件需要映射的Dao接口
-->
<mapper namespace="com.yiidian.dao.CustomerDao">

    <!--查询所有-->
    <select id="findAll" resultType="com.yiidian.domain.Customer">
        select * from t_customer
    </select>

    <!--1.添加方法-->
    <insert id="save" parameterType="com.yiidian.domain.Customer">
        INSERT INTO t_customer(NAME,gender,telephone) VALUES(#{name},#{gender},#{telephone})
    </insert>

    <!--2.修改方法-->
    <update id="update" parameterType="com.yiidian.domain.Customer">
        UPDATE t_customer SET
        NAME = #{name},
        gender = #{gender},
        telephone = #{telephone}
        WHERE id = #{id}
    </update>

    <!--查询一个-->
    <select id="findById" parameterType="integer" resultType="com.yiidian.domain.Customer">
        select * from t_customer where id = #{id}
    </select>

    <!--条件查询-->
    <select id="findByName" parameterType="string" resultType="com.yiidian.domain.Customer">
        select * from t_customer where name like #{name}
    </select>

    <!--删除-->
    <delete id="delete" parameterType="integer">
        delete from t_customer where id = #{id}
    </delete>
</mapper>

1.4 编写测试类

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/**
 * MyBatis测试类 - 传统Dao写法
 */
public class TestCustomerDao {

    /**
     * 添加
     */
    @Test
    public void testSave(){
        //1.获取SqlSession对象
        SqlSession session = MyBatisUtils.getSession();

        //2.创建传统Dao实现类对象
        CustomerDao customerDao = new CustomerDaoImpl();

        //3.调用save方法
        Customer customer = new Customer();
        customer.setName("小苍");
        customer.setGender("女");
        customer.setTelephone("15755556666");
        customerDao.save(customer);


        //4.关闭连接
        session.close();
    }

    /**
     * 修改
     */
    @Test
    public void testUpdate(){
        //1.获取SqlSession对象
        SqlSession session = MyBatisUtils.getSession();

        //2.创建传统Dao实现类对象
        CustomerDao customerDao = new CustomerDaoImpl();

        //3.调用update方法
        Customer customer = new Customer();
        customer.setId(5);
        customer.setName("小泽");
        customer.setGender("女");
        customer.setTelephone("15755556666");
        customerDao.update(customer);

        session.commit();

        //4.关闭连接
        session.close();
    }

    /**
     * 查询所有
     */
    @Test
    public void testFindAll(){
        //1.获取SqlSession对象
        SqlSession session = MyBatisUtils.getSession();

        //2.创建传统Dao实现类对象
        CustomerDao customerDao = new CustomerDaoImpl();

        //3.调用findAll方法
        List<Customer> list = customerDao.findAll();

        for(Customer cust:list){
            System.out.println(cust);
        }

        //4.关闭连接
        session.close();
    }

    /**
     * 查询一个
     */
    @Test
    public void testFindById(){
        //1.获取SqlSession对象
        SqlSession session = MyBatisUtils.getSession();

        //2.创建传统Dao实现类对象
        CustomerDao customerDao = new CustomerDaoImpl();

        //3.调用findById方法
        Customer customer = customerDao.findById(3);

        System.out.println(customer);

        //4.关闭连接
        session.close();
    }

    /**
     * 条件查询
     */
    @Test
    public void testFindByName(){
        //1.获取SqlSession对象
        SqlSession session = MyBatisUtils.getSession();

        //2.创建传统Dao实现类对象
        CustomerDao customerDao = new CustomerDaoImpl();

        //3.调用findByName方法
        List<Customer> list = customerDao.findByName("%小%");

        for(Customer cust:list){
            System.out.println(cust);
        }

        //4.关闭连接
        session.close();
    }

    /**
     * 删除
     */
    @Test
    public void testDelete(){
        //1.获取SqlSession对象
        SqlSession session = MyBatisUtils.getSession();

        //2.创建传统Dao实现类对象
        CustomerDao customerDao = new CustomerDaoImpl();

        //3.调用findByName方法
        customerDao.delete(5);

        // 提交事务
        session.commit();

        //4.关闭连接
        session.close();
    }
}

2 Mapper代理接口

2.1 编写CustomerDao接口

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/**
 * Dao接口
 */
public interface CustomerDao {

    /**
     * 查询所有用户
     */
    public List<Customer> findAll();

    /**
     * 添加
     */
    public void save(Customer customer);

    /**
     * 修改
     */
    public void update(Customer customer);

    /**
     * 查询一个
     */
    public Customer findById(Integer id);

    /**
     * 条件查询
     */
    public List<Customer> findByName(String name);

    /**
     * 删除
     */
    public void delete(Integer id);
}

2.2 编写CustomerDao.xml映射

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<?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">
<!--
   namespace: 用于指定该映射文件需要映射的Dao接口
-->
<mapper namespace="com.yiidian.dao.CustomerDao">

    <!--查询所有-->
    <select id="findAll" resultType="com.yiidian.domain.Customer">
        select * from t_customer
    </select>

    <!--1.添加方法-->
    <insert id="save" parameterType="com.yiidian.domain.Customer">
        INSERT INTO t_customer(NAME,gender,telephone) VALUES(#{name},#{gender},#{telephone})
    </insert>

    <!--2.修改方法-->
    <update id="update" parameterType="com.yiidian.domain.Customer">
        UPDATE t_customer SET
        NAME = #{name},
        gender = #{gender},
        telephone = #{telephone}
        WHERE id = #{id}
    </update>

    <!--查询一个-->
    <select id="findById" parameterType="integer" resultType="com.yiidian.domain.Customer">
        select * from t_customer where id = #{id}
    </select>

    <!--条件查询-->
    <select id="findByName" parameterType="string" resultType="com.yiidian.domain.Customer">
        select * from t_customer where name like #{name}
    </select>

    <!--删除-->
    <delete id="delete" parameterType="integer">
        delete from t_customer where id = #{id}
    </delete>
</mapper>

2.3 编写测试类

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/**
 * MyBatis测试类 - Mapper代理接口
 */
public class TestCustomerDao2 {

    /**
     * 添加
     */
    @Test
    public void testSave(){
        //1.获取SqlSession对象
        SqlSession session = MyBatisUtils.getSession();

        //2.生成Dao代理对象
        CustomerDao customerDao = session.getMapper(CustomerDao.class);

        //3.调用save方法
        Customer customer = new Customer();
        customer.setName("小苍");
        customer.setGender("女");
        customer.setTelephone("15755556666");
        customerDao.save(customer);


        //4.关闭连接
        session.close();
    }

    /**
     * 修改
     */
    @Test
    public void testUpdate(){
        //1.获取SqlSession对象
        SqlSession session = MyBatisUtils.getSession();

        //2.生成Dao代理对象
        CustomerDao customerDao = session.getMapper(CustomerDao.class);

        //3.调用update方法
        Customer customer = new Customer();
        customer.setId(5);
        customer.setName("小泽");
        customer.setGender("女");
        customer.setTelephone("15755556666");
        customerDao.update(customer);

        session.commit();

        //4.关闭连接
        session.close();
    }

    /**
     * 查询所有
     */
    @Test
    public void testFindAll(){
        //1.获取SqlSession对象
        SqlSession session = MyBatisUtils.getSession();

        //2.生成Dao代理对象
        CustomerDao customerDao = session.getMapper(CustomerDao.class);

        //3.调用findAll方法
        List<Customer> list = customerDao.findAll();

        for(Customer cust:list){
            System.out.println(cust);
        }

        //4.关闭连接
        session.close();
    }

    /**
     * 查询一个
     */
    @Test
    public void testFindById(){
        //1.获取SqlSession对象
        SqlSession session = MyBatisUtils.getSession();

        //2.生成Dao代理对象
        CustomerDao customerDao = session.getMapper(CustomerDao.class);

        //3.调用findById方法
        Customer customer = customerDao.findById(5);

        System.out.println(customer);

        //4.关闭连接
        session.close();
    }

    /**
     * 条件查询
     */
    @Test
    public void testFindByName(){
        //1.获取SqlSession对象
        SqlSession session = MyBatisUtils.getSession();

        //2.生成Dao代理对象
        CustomerDao customerDao = session.getMapper(CustomerDao.class);

        //3.调用findByName方法
        List<Customer> list = customerDao.findByName("%小%");

        for(Customer cust:list){
            System.out.println(cust);
        }

        //4.关闭连接
        session.close();
    }

    /**
     * 删除
     */
    @Test
    public void testDelete(){
        //1.获取SqlSession对象
        SqlSession session = MyBatisUtils.getSession();

        //2.生成Dao代理对象
        CustomerDao customerDao = session.getMapper(CustomerDao.class);

        //3.调用findByName方法
        customerDao.delete(5);

        // 提交事务
        session.commit();

        //4.关闭连接
        session.close();
    }
}

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