二、两种方法查询数据库

一、获取session，session直接调用mapper配置文件里写的方法。

二、获取session，session再通过生成mapper接口实现类来查询。这里需要注意的就是，如mapper/StudentMapper.java接口需要同xmlmaper文件的namespace一致。

public class TestXmlBuild1 {
    public static SqlSessionFactory sqlMapper = null;

    @Before
    public void setUpClass() throws IOException {
        String resource = "config/Configuration1.xml";
        Reader reader = Resources.getResourceAsReader(resource);
        sqlMapper = new SqlSessionFactoryBuilder().build(reader);
    }

    @Test
    public void test1() {
        SqlSession session = sqlMapper.openSession();
        //第一种方法，直接调用，名字要和<mapper namespace="mapper.StudentMapper">匹配
        try {
            Student student = (Student) session.selectOne("mapper.StudentMapper.get", "ttt");
            System.out.println(student);
        } finally {
            session.close();
        }
    }
    
    @Test
    public void test2() {
        SqlSession session = sqlMapper.openSession();
        //第二种方法，通过接口，mapper名字需要和<mapper namespace="mapper.StudentMapper">匹配
        try {
            StudentMapper studentMapper = session.getMapper(StudentMapper.class);
            Student student = studentMapper.get("ttt"); 
            System.out.println(student);
        } finally {
            session.close();
        }
    }
}

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="mapper.StudentMapper">
    <resultMap type="Student" id="StudentResultMap">
        <id property="id" column="id" />
        <result property="name" column="name" />
        <result property="password" column="password" />
        <result property="sex" column="sex" />
        <result property="college" column="college" />
        <collection property="scores" column="sid" javaType="ArrayList" ofType="Score" resultMap="Score.ScoreResultMap" />
    </resultMap>
    <select id="get" parameterType="String" resultMap="StudentResultMap">
        SELECT * FROM sc_student st LEFT OUTER JOIN sc_score sc ON st.id=sc.sid WHERE st.id=#{id}
    </select>
    <insert id="insert" parameterType="Student">
        insert into sc_student (id,name,password,sex,college) values
        (#{id},#{name},#{password},#{sex},#{college})
    </insert>
    <update id="update" parameterType="Student">
        UPDATE sc_student SET id=#{id},name=#{name},password=#{password},
        sex=#{sex},college=#{college} WHERE id=#{id}
    </update>
    <delete id="delete" parameterType="Student">
        DELETE FROM sc_student WHERE id = #{id}
    </delete>
</mapper>

mapper/StudentMapper.java

package mapper;

import entity.Student;

public interface StudentMapper {
    //@Select("SELECT * FROM blog WHERE id = #{id}") //不写mapper可以用这种方式代替，没试过。
    public Student get(String id); 
}

Configuration.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>
    <!-- 用于建立会话的变量，可以从文件中读取 -->
    <properties resource="config/config.properties">
        <property name="driver" value="com.mysql.jdbc.Driver" />
        <property name="url" value="jdbc:mysql://localhost:3306/test" />
        <property name="username" value="root" />
        <property name="password" value="asd123" />
    </properties>

    <!-- 可以不设置 -->
    <!-- <setting></setting> -->
    
    <typeAliases>
        <typeAlias alias="Student" type="entity.Student"></typeAlias>
        <typeAlias alias="Score" type="entity.Score"></typeAlias>
    </typeAliases>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC" />
            <dataSource type="POOLED">
                <property name="driver" value="${driver}" />
                <property name="url" value="${url}" />
                <property name="username" value="${username}" />
                <property name="password" value="${password}" />
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="mapper/StudentMapper.xml" />
        <mapper resource="entity/ScoreMapper.xml" />
    </mappers>
</configuration>