mybatis框架学习

2022-11-02 07:34:22 #framework

Maven导入jar包


<dependencies>

    <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.7</version>
    </dependency>

    <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>8.0.30</version>
    </dependency>

    <!-- https://mvnrepository.com/artifact/junit/junit -->
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.13.2</version>
    </dependency>

    <!-- https://mvnrepository.com/artifact/log4j/log4j -->
    <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>1.2.17</version>
    </dependency>

    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>RELEASE</version>
        <scope>compile</scope>
    </dependency>

</dependencies>

mybatis核心配置文件

在配置文件中所有的标签都要按照指定的顺序放置
properties settings typeAliases typeHandlers objectFactory
objectWrapperFactory reflectorFactory plugins environments
databaseIdProvider mappers

引入外部资源(数据库配置文件)


<!-- 引入外部资源-->
<properties resource="db.properties">
    <!--  添加属性 优先使用外部配置文件-->
    <property name="username" value="root"/>
</properties>

配置文件设置

日志配置 STDOUT_LOGGING Mybatis默认日志,LOG4J 第三方日志(需导入对应jar包)

<settings>
    <!-- 系统日志-->
    <!--        <setting name="logImpl" value="STDOUT_LOGGING"/>-->
    <setting name="logImpl" value="LOG4J"/>
</settings>

LOG4J 配置

log4j.rootLogger = debug,console,file

log4j.appender.console = org.apache.log4j.ConsoleAppender
log4j.appender.console.Target = System.out
log4j.appender.console.Threshold = DEBUG
log4j.appender.console.layout = org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern = [%c]-%m%n

log4j.appender.file = org.apache.log4j.FileAppender
log4j.appender.file.File = ./log/log4j.log
log4j.appender.file.Threshold = DEBUG
log4j.appender.file.layout = org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern = [%p][%d{yyyy-MM--dd}][%c]%m%n

log4j.logger.org.mybatis=dubug
log4j.logger.java.sql=dubug
log4j.logger.java.sql.Statement=dubug
log4j.logger.java.sql.PreparedStatement=dubug
log4j.logger.java.sql.ResultSet=dubug

开启驼峰命名自动映射

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<settings>
    <setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>

实体类起别名

可以使用过注解 “@Alias“ 起别名


@Alias("hello")
public class User {
    private int id;
    private String name;
    private String pwd;
}

给包起别名子类可以直接使用类名

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<typeAliases>
    <package name="com.hg.pojo"/>
</typeAliases>

给实体类起别名

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<typeAliases>
    <typeAlias type="com.hg.pojo.User" alias="user"/>
</typeAliases>

环境配置

一个Mybatis可以有多套环境配置,但只会生效一个,JDBC参数可以引入外部资源,也可以手动添加

<environments default="development">
    <!--        默认环境,可以有多套环境-->
    <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>

Mapper文件映射

当mapper.xml文件和Mapper接口类在同一个包下时可以使用class进行映射
当mapper.xml文件和Mapper接口类所在包同名时用resource进行映射
mapper.xml文件可使用包扫描
mapper.xml文件必须和接口类同名同包

<mappers>
    <mapper resource="com/hg/mapper/UserMapper.xml"/>
    <!--        和接口在同一个包下-->
    <!--        <mapper class="com.hg.mapper.UserMapper"/>-->
    <!--        扫描包-->
    <!--        <package name="com/hg/mapper"/>-->
</mappers>

Mapper文件编写

每个mapper.xml文件都对应一个mapper接口类,使用 namespace 引入命名空间
在idea编译器中连接数据后,配置sql方言可以在mapper.xml进行智能提醒
在mapper.xml文件中java的包装类型都是用其对应的基本类型比如Integer类型使用时为_int
java基础类型使用时须在类型前添加 _ 比如int类型使用时为_int
使用引用类时需添加完整路径

基础数据库的 `CRUD` 操作代码示例

<select id="getUserList" resultType="hello">
    select *
    from mybatis.user
</select>

<insert id="addUser" parameterType="com.hg.pojo.User">
    insert into mybatis.user(name, pwd)
    values (#{name}, #{pwd})
</insert>

<update id="updateUser" parameterType="com.hg.pojo.User">
    update mybatis.user
    set name=#{name},
        pwd=#{pwd}
    where id = #{id}
</update>

<delete id="delUser" parameterType="_int">
    delete
    from mybatis.user
    where id = #{id}
</delete>

使用注解实现查询

1 2	@Select("select * from mybatis.user where id=#{id}") User getUserById(int id);

万能的Map

1	List<User> getUserList2(Map<String,Object> map);

<!--    分页查询-->
<select id="getUserList2" resultType="com.hg.pojo.User" parameterType="map">
    select * from mybatis.user limit #{currentPageNode},#{pageSize};
</select>

public class UserDaoTest {
    @Test
    public void getUserById2(){
        //第一步：获得SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        //方式一：getMapper
        UserMapper userDao = sqlSession.getMapper(UserMapper.class);
        Map<String, Object> map = new HashMap<>();
        map.put("currentPageNode",0);
        map.put("pageSize",2);
      
        List<User> userList2 = userDao.getUserList2(map);
        //关闭SqlSession
        sqlSession.close();
    }
}

mapper层操作数据库Demo

新建数据库操作工具类获取sqlSessionFactory

public class MybatisUtils {
    private static SqlSessionFactory sqlSessionFactory;

    static {
        try {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    /**
     *
     * 既然有了 SqlSessionFactory，顾名思义，我们可以从中获得 SqlSession 的实例。
     * SqlSession 提供了在数据库执行 SQL 命令所需的所有方法。
     *
     */
    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }
}

使用sqlSession中的getMaper方法用过反射获取操作类对象
通过获取到的对象使用具体方法,并传入所需参数

public class UserDaoTest {
    @Test
    public void getUserList() {
        //第一步：获得SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //方式一：getMapper
        UserMapper userDao = sqlSession.getMapper(UserMapper.class);
        List<User> userList = userDao.getUserList();
        for (User user : userList) {
            System.out.println(user);
        }
        //关闭SqlSession
        sqlSession.close();
    }
}

数据库查询

多对一

学生实体类

@Data
@ToString
@AllArgsConstructor
@NoArgsConstructor
public class Student {
    private int id;
    private String name;
    private Teacher teacher;
}

老师实体类

@Data
@AllArgsConstructor
@NoArgsConstructor
@ToString
public class Teacher {
    private int id;
    private String name;
}

接口

public interface StudentMapper {

    List<Student> getStudent();

    List<Student> getStudent2();

}

测试

public class MapperTest {
    //生成日志对象
    static Logger logger = Logger.getLogger(MapperTest.class);

    @Test
    public void getStudent1() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        StudentMapper students = sqlSession.getMapper(StudentMapper.class);
        List<Student> studentsList = students.getStudent();
      
        sqlSession.close();
    }
}

方式一

子查询查询所有学生信息,根据id查询对应的老师

<select id="getStudent" resultMap="StudentTeacher">
    select * from mybatis.student;
</select>

<resultMap id="StudentTeacher" type="Student">
    <result property="id" column="id"/>
    <result property="name" column="name"/>
    <!--        复杂属性单独处理, association:对象   collection:集合 -->
    <association property="teacher" column="tid" javaType="Teacher" select="getTeacher"/>
</resultMap>

<select id="getTeacher" resultType="Teacher">
    select * from mybatis.teacher where id = #{tid};
</select>

方式二

按结果嵌套查询

<select id="getStudent2" resultMap="StudentTeacher2">
    select s.id sid,s.name sname,t.name tname
    from mybatis.student s,mybatis.teacher t
    where s.tid = t.id;
</select>

<resultMap id="StudentTeacher2" type="Student">
    <result property="id" column="sid"/>
    <result property="name" column="sname"/>
    <association property="teacher" javaType="Teacher">
        <result property="name" column="tname"/>
    </association>
</resultMap>

一对多