MyBatis学习笔记2

CRUD

1.namespace

namespace中的包名要和mapper接口的包名一致!

2.select

选择查询语句

id:就是对应的namespace中的方法名;

resultType:Sql语句执行的返回值!

parameterType:参数类型

增删改必须提交事务:sqlSession.commit();

1.编写接口

List<User> getUserList();
    //根据id查询用户
    User getUserById(int id);
    //insert一个用户;
    int addUser(User user);
    //修改用户
    int updateUser(User user);
    //删除用户
    int deleteUser(int id);

2.编写对应的mapper中的Sql语句

<select id="getUserList" resultType="pojo.User">
        select * from mybatis.user
    select>
    <select id="getUserById" parameterType="int" resultType="pojo.User">
        select * from mybatis.user where id = #{id}
    select>
    <insert id="addUser" parameterType="pojo.User" >
       insert into mybatis.user (id,name,pwd) values (#{id},#{name},#{pwd});
    insert>
    <update id="updateUser" parameterType="pojo.User">
        update mybatis.user set name=#{name},pwd=#{pwd} where id = #{id};
    update>
    <delete id="deleteUser" parameterType="int">
        delete from mybatis.user where id= #{id};
    delete>

3.测试

public  void test(){
       //1.获得SqlSession对象
       SqlSession sqlSession = MybatisUtils.getSqlSession();
       //2.执行Sql--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();
   }
public void getUserById(){
       SqlSession sqlSession1 = MybatisUtils.getSqlSession();
       UserMapper mapper = sqlSession1.getMapper(UserMapper.class);
       User user = mapper.getUserById(1);
       System.out.println(user);
       sqlSession1.close();
   }

3.Insert

public void addUser(){
       SqlSession sqlSession = MybatisUtils.getSqlSession();
       UserMapper mapper = sqlSession.getMapper(UserMapper.class);
       mapper.addUser(new User(5,"jim","123123"));
       //提交事务
       sqlSession.commit();
       sqlSession.close();
   }

4.Update

public void updateUser(){
       SqlSession sqlSession = MybatisUtils.getSqlSession();
       UserMapper mapper = sqlSession.getMapper(UserMapper.class);
       mapper.updateUser(new User(5,"jack2","123456"));
       sqlSession.commit();
       sqlSession.close();
   }

5.Delete

public  void deleteUser(){
       SqlSession sqlSession = MybatisUtils.getSqlSession();
       UserMapper mapper = sqlSession.getMapper(UserMapper.class);
       mapper.deleteUser(5);

       sqlSession.commit();
       sqlSession.close();
   }

万能的Map

假设我们的实体类或者数据库中的表,字段或者参数过多,我们应当考虑使用Map!

int addUser2(Map<String,Object>map);
<insert id="addUser2" parameterType="map" >
       insert into mybatis.user (id,name,pwd) values (#{userid},#{username},#{userpwd});
    insert>
public void addUser2(){
       SqlSession sqlSession = MybatisUtils.getSqlSession();
       UserMapper mapper = sqlSession.getMapper(UserMapper.class);
       Map<String, Object> map = new HashMap<String, Object>();
       map.put("userid",5);
       map.put("username","jack3");
       map.put("userpwd","123123");

       mapper.addUser2(map);
       sqlSession.commit();
       sqlSession.close();
   }

模糊查询

1.在Java代码执行的时候,传递通配符%%

List<User> userList = userDao.getUserList2("%李%");
select * from mybatis.user where name like #{values};

2.在sql拼接中使用通配符

select * from mybatis.user where name like "%"#{values}"%";
List<User> userList = userDao.getUserList2("李");

配置解析

mybatis-config.xml

mybatis的配置文件包含了会深深影响MyBatis行为的设置和属性信息

configuration(配置)
properties(属性)
settings(设置)
typeAliases(类型别名)
typeHandlers(类型处理器)
objectFactory(对象工厂)
plugins(插件)
environments(环境配置)
environment(环境变量)
transactionManager(事务管理器)
dataSource(数据源)
databaseIdProvider(数据库厂商标识)
mappers(映射器)

db.properties

driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybatis?serverTimezone=Asia/Shanghai&useSSL=false&useUnicode=true&characterEncoding=UTF-8
username=root
password=123456

可以直接引入外部文件

可以在其中增加一些属性配置

如果两个文件有同一个字段,优先使用外部配置文件的!

类型别名(typeAliases)


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

扫描实体类的包,它的默认别名就是这个类的类名,首字母小写

<typeAliases>
        <package name="pojo"/>
typeAliases>

实体类比较少的时候,使用第一种

实体类多的时候,使用第二种

第一种可以DIY别名,第二种不可以(可以使用注解@alias)

映射器

<mappers>
      <mapper resource="dao/UserMapper.xml"/>
  mappers>

作用域和生命周期

SqlSessionFactoryBuilder:一旦创建SqlSession就不在需要,一般设置为局部变量

SqlSessionFactory:可以理解为数据库连接池,一旦被创建就一直存在

SqlSession:可以理解为连接池中的请求,实例是不安全的线程,不能被共享,使用完毕就关闭。

属性名和字段名不一致问题

解决办法:起别名

<select id="getUserById" parameterType="int" resultType="user">
        select id,name, pwd as password from mybatis.user where id =#{id}
    select>

resultMap结果集映射

<resultMap id="UserMap" type="user">
        <result column="id" property="id"/>
        <result column="name" property="name"/>
        <result column="pwd" property="password"/>
    resultMap>
<select id="getUserById" resultMap="UserMap">
        select * from mybatis.user where id = #{id}
    select>

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