Mybatis学习记录(3)

1.输出映射和输入映射

Mapper.xml映射文件定义了操作数据库的sql,每个sql就是一个statement,映射文件是mybatis的核心。

(1)parameterType(输入类型)

   1.传递简单类型

使用占位符#{},或者${}进行sql拼接。

2.传递pojo对象

使用ognl表达式解析对象字段的值,#{}或者${}括号中的值 为pojo属性名称。

3.传递pojo包装对象

开发中可以通过使用pojo传递查询条件,查询的条件可能是综合的查询条件,这时可以使用包装对象传递输入参数。

包装对象：Pojo类中的一个属性是另一个pojo

即新建一个queryInfo类将所需要的查询条件全部声明到此类中,并生成get,set方法。

编写QueryInfo类 UserQueryInfo.java

package com.javaweb.mybatis.model.queryInfo;

import java.io.Serializable;

import com.javaweb.mybatis.model.User;

public class UserQueryInfo implements Serializable{

    /**
     *
     */
    private static final long serialVersionUID = 1L;

    private User user;

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

}

Mapper.xml配置文件

<!-- 根据用户名模糊查询 -->
    <select id="findUserByQueryInfo" parameterType="com.javaweb.mybatis.model.queryInfo.UserQueryInfo" resultType="com.javaweb.mybatis.model.User">
        select * from mybatis_user where username like "%${user.userName}%"
    </select>

Mapper接口

public interface UserMapper {
    /**
     * 遵循四个原则
     * 1.接口方法名 ==User.xml中的id名
     * 2.返回值类型与Mapper.xml的返回值类型一致
     * 3.方法的入参类型与Mapper.xml中的入参类型一致
     * 4.命名空间绑定此接口,即Mapper.xml的namespace是此接口的路径
     */

    public List<User> findUserByQueryInfo(UserQueryInfo queryInfo);

Jubit单元测试类:

    @Test
    public void testMapperQueryInfo() throws Exception{
        //加载核心配置文件
        String resource="sqlMapConfig.xml";
        InputStream in=Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession=sqlSessionFactory.openSession();

        //SqlSession帮我生成一个实现类
        UserMapper userMapper=sqlSession.getMapper(UserMapper.class);

        UserQueryInfo queryInfo =new UserQueryInfo();
        User user=new User();
        user.setUserName("王");
        queryInfo.setUser(user);

        List<User> userList=userMapper.findUserByQueryInfo(queryInfo);
        for(User u:userList){
            System.out.println(u);
        }
    }

2.resultType(输出类型)

  (1)输出简单类型

需求查询用户表的数据总条数

Mapper接口:

public interface UserMapper {
    /**
     * 遵循四个原则
     * 1.接口方法名 ==User.xml中的id名
     * 2.返回值类型与Mapper.xml的返回值类型一致
     * 3.方法的入参类型与Mapper.xml中的入参类型一致
     * 4.命名空间绑定此接口,即Mapper.xml的namespace是此接口的路径
     */

    //查询数据条数
    public Integer countUser();

Mapper.xml配置文件

    <!-- 查询数据条数 -->
    <select id="countUser" resultType="Integer">
        select count(1) from mybatis_user  where 1=1 and id=2
    </select>

Junit单元测试类:

@Test
    public void testMapperCountUserQueryInfo() throws Exception{
        //加载核心配置文件
        String resource="sqlMapConfig.xml";
        InputStream in=Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession=sqlSessionFactory.openSession();

        //SqlSession帮我生成一个实现类
        UserMapper userMapper=sqlSession.getMapper(UserMapper.class);

        Integer countUser = userMapper.countUser();
        System.out.println(countUser);
    }

(2)输出pojo对象

见上一章

(3)输出pojo列表

见上一章

3.resultMap(输出类型)

  resultType可以指定将查询结果映射为pojo,但需要pojo的属性名和sql查询的列名一致才能映射成功。

但是如果是sql查询字段名和pojo的属性名不一致,就可以通过resultMap将字段名和属性名手动做一个对应关系,resultMap实质上还需要将查询结果映射到pojo对象中。

resultMap可以实现将映射为复杂类型的pojo,比如在查询结果映射对象中包括pojo和list实现一对一查询和一对多查询。

示例:查询订单表order中的所有数据

数据库表构造如下:

Order对象order.java

public class Order implements Serializable{

    /**
     *
     */
    private static final long serialVersionUID = 1L;

    private String id;
    private String userId;
    private Integer number;
    private String note;
    private Date createTime;
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public String getUserId() {
        return userId;
    }
    public void setUserId(String userId) {
        this.userId = userId;
    }
    public Integer getNumber() {
        return number;
    }
    public void setNumber(Integer number) {
        this.number = number;
    }
    public String getNote() {
        return note;
    }
    public void setNote(String note) {
        this.note = note;
    }
    public Date getCreateTime() {
        return createTime;
    }
    public void setCreateTime(Date createTime) {
        this.createTime = createTime;
    }
    @Override
    public String toString() {
        return "Order [id=" + id + ", userId=" + userId + ", number=" + number + ", note=" + note + ", createTime="
                + createTime + "]";
    }

OrderMapper.java接口

/**
 * 订单接口
 * @author fanyukai
 *
 */
public interface OrderMapper {

    public List<Order> orderList();
}

Mapper.xml配置文件

<mapper namespace="com.javaweb.mybatis.mapper.OrderMapper">
    <!-- id：设置resultMap的id -->
    <resultMap type="com.javaweb.mybatis.model.Order" id="orders">
        <!-- 定义主键 -->
        <!-- property:主键在pojo的属性名 -->
        <!-- colunm:主键在数据库中的列名 -->
        <id property="id" column="id" />

        <!-- 定义普通属性 -->
        <result column="user_id" property="userId"/>
    </resultMap>

    <!-- 查询所有订单 -->
    <select id="orderList" resultMap="orders">
        select id,user_id,number,note,createtime from mybatis_orders
    </select>
</mapper>

Junit单元测试类：

@Test
    public void testMapperOrderList() throws Exception{
        //加载核心配置文件
        String resource="sqlMapConfig.xml";
        InputStream in=Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession=sqlSessionFactory.openSession();

        //SqlSession帮我生成一个实现类
        OrderMapper orderMapper = sqlSession.getMapper(OrderMapper.class);

        List<Order> orderList=orderMapper.orderList();
        for(Order orders :orderList){
            System.out.println(orders);
        }
    }

3.动态sql

(1)通过mybatis提供的各种标签方法实现动态拼接sql

<sql>和<include>标签

(2)where,if 标签

4.关联查询

一对一关联:一份订单对应一个用户

使用resultMap,定义专门的resultMap用于映射一对一查询结果

sql语句:

      select
        o.id,
        o.user_id,
        o.number,
        o.note,
        o.createtime,
        u.id,
        u.username
        FROM mybatis_orders o
        LEFT JOIN mybatis_user u
        ON o.user_id=u.id

改造pojo类

public class Order implements Serializable{

    /**
     *
     */
    private static final long serialVersionUID = 1L;

    private String id;
    private String userId;
    private Integer number;
    private String note;
    private Date createTime;

    //附加对象 用户对象
    private User user;

    public User getUser() {
        return user;
    }
    public void setUser(User user) {
        this.user = user;
   /* 后面get,set方法省略*/

Mapper.xml配置文件

<resultMap type="com.javaweb.mybatis.model.Order" id="order">
        <!-- 定义普通属性 -->
        <id     column="id" property="id"/>
        <result column="user_id" property="userId"/>
        <result column="number" property="number"/>
        <result column="createtime" property="createTime"/>

        <!-- 一对一 -->
        <association property="user" javaType="com.javaweb.mybatis.model.User" >
            <id column="id" property="user_id"/>
            <result column="userName" property="userName"/>
        </association>
    </resultMap>

    <!-- 一对一关联查询 以订单为中心关联用户 -->
    <select id="selectOrder" resultMap="order">
        select
        o.id,
        o.user_id,
        o.number,
        o.note,
        o.createtime,
        u.id,
        u.username
        FROM mybatis_orders o
        LEFT JOIN mybatis_user u
        ON o.user_id=u.id
    </select>

Mapper接口:

public interface OrderMapper {

    //一对一关联查询 以订单为中心关联用户

    public List<Order> selectOrder();
    

Junit单元测试类:

@Test
    public void testMapperOrderOneToOne() throws Exception{
        //加载核心配置文件
        String resource="sqlMapConfig.xml";
        InputStream in=Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession=sqlSessionFactory.openSession();

        //SqlSession帮我生成一个实现类
        OrderMapper orderMapper = sqlSession.getMapper(OrderMapper.class);

        List<Order> orderList=orderMapper.selectOrder();
        for(Order orders :orderList){
            System.out.println(orders);
        }
    }

一对多关联:一个用户对应多个订单

sql语句

     select
        o.id,
        o.user_id,
        o.number,
        o.note,
        o.createtime,
        u.username
        FROM mybatis_user u
        LEFT JOIN mybatis_orders o
        ON o.user_id=u.id

改造pojo类 User.java:

public class User implements Serializable{

    /**
     * user表的pojo对象
     */
    private static final long serialVersionUID = 1L;
    private String id;
    private String userName;
    private String userAge;
    private String userSex;
    private String userAddress;

    //附加对象list 一对多
    private List<Order> orderList;

    public List<Order> getOrderList() {
        return orderList;
    }
    public void setOrderList(List<Order> orderList) {
        this.orderList = orderList;
    }
/*后面get,set方法省略*/

Mapper.xml配置文件:

<!-- 一对多 以用户为中心-->
    <resultMap type="com.javaweb.mybatis.model.User" id="user">
        <id column="id" property="id"/>
        <result column="username" property="userName"/>

        <!-- 一对多 -->
        <collection property="orderList" ofType="com.javaweb.mybatis.model.Order">
            
            <!-- 配置主键,是关联Order的唯一标识 -->
            <id column="id" property="id"/>
            <result column="number" property="userName"/>
            <result column="user_id" property="userId"/>
            <result column="note" property="note"/>
            <result column="createtime" property="createTime"/>
        </collection>

    </resultMap>
    <select id="selectUserList" resultMap="order">
        select
        o.id,
        o.user_id,
        o.number,
        o.note,
        o.createtime,
        u.username
        FROM mybatis_user u
        LEFT JOIN mybatis_orders o
        ON o.user_id=u.id
    </select>

Mapper接口:

public interface OrderMapper {

    //一对多关联
    public List<User> selectUserList();
}

Junit单元测试类:

@Test
    public void testMapperOrderOneToMany() throws Exception{
        //加载核心配置文件
        String resource="sqlMapConfig.xml";
        InputStream in=Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession=sqlSessionFactory.openSession();

        //SqlSession帮我生成一个实现类
        OrderMapper orderMapper = sqlSession.getMapper(OrderMapper.class);

        List<User> selectUserList = orderMapper.selectUserList();
        for(User user :selectUserList){
            System.out.println(user);
        }
    }