MyBatis高级 - 技术栈

文章目录

一、动态sql
二、分页
- 1、分页的使用步骤
三、mybatis多表查询

一、动态sql

准备工作：在昨天整合的代码中添加UserMapper接口和配置文件

java 复制代码

public interface UserMapper {
    List<User> queryUserByCondition(User user);
}

<?xml version="1.0" encoding="UTF-8" ?>
<!--MyBatis的DTD约束-->
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.linjiu.dao.UserMapper">

    <select id="queryUserByCondition" resultType="com.linjiu.model.User" parameterType="com.linjiu.model.User">
      
    </select>
</mapper>

1、if

格式

<if test="条件">
    sql 语句
</if>
当条件成立的时候，会执行sql语句
if (条件){
	sql 语句
}

案例

<select id="queryUserByCondition" resultType="com.linjiu.model.User" parameterType="com.linjiu.model.User">
    select id,username,password,age,phone from user where 1=1
    <if test="age!=null and age!=''">
        and age=#{age}
    </if>
    <if test="phone!=null and phone!=''">
        and phone=#{phone}
    </if>
</select>

java代码

@Test
public void test02(){
    User user = new User();
    user.setPhone("120");
    user.setAge(11);
    List<User> users = userMapper.queryUserByCondition(user);
    System.out.println(users);
}

运行日志

DEBUG [main] - ==> Preparing: select id,username,password,age,phone from user where 1=1 and age=? and phone=?

DEBUG [main] - ==> Parameters: 11(Integer), 120(String)

2、choose...when...otherwise...

格式

<choose>
    <when test="条件1"> 
    	sql语句1
    </when>
    
    <when test="条件2"> 
    	sql语句2
    </when>
    
    <otherwise>
        sql语句3
    </otherwise>
</choose>

和我们java的if...else if ...else格式一样
当条件1成立，那么就不会执行后面的代码

案例

<select id="queryUserByCondition" resultType="com.linjiu.model.User" parameterType="com.linjiu.model.User">
    select id,username,password,age,phone from user where 1=1
    <choose>
        <when test="age!=null and age!=''">
            and age=#{age}
        </when>
        <when test="phone!=null and phone!=''">
            and phone=#{phone}
        </when>
        <otherwise>
            and password='112233'
        </otherwise>
    </choose>
</select>

3、where

markdown 复制代码

# 说明
	- 标签里边的if 至少有一个成立，就会动态添加一个where，如果都不成立，不添加where 
	- 第一个if条件成立的，会自动去除连接符and 或者 or

案例

<select id="queryUserByCondition" resultType="com.linjiu.model.User" parameterType="com.linjiu.model.User">
    select id,username,password,age,phone from user
    <where>
        <if test="age!=null and age!=''">
            and age=#{age}
        </if>
        <if test="phone!=null and phone!=''">
            and phone=#{phone}
        </if>
    </where>
</select>

4、set

说明

说明： 动态添加了set字段，也会动态的去掉最后一个逗号

案例

<update id="updateUser" parameterType="com.linjiu.model.User">
    update user
    <set>
        <if test="username!=null and username!=''">username=#{username},</if>
        <if test="password!=null and password!=''">password=#{password},</if>
    </set>
    where id=#{id}
</update>

代码

@Test
public void test03(){
    User user = new User();
    user.setId(1);
    user.setUsername("哥哥123");
    user.setPassword("332211");
    String message = userMapper.updateUser(user)>0?"成功":"失败";
    System.out.println(message);
}

5、foreach

说明：适用于 id in (x,x,x)

格式

xml 复制代码

循环遍历标签。适用于多个参数或者的关系。
<foreach collection=""open=""close=""item=""separator="">
    获取参数
</foreach>

案例

<select id="queryUsersByIds" resultType="com.linjiu.model.User"
        parameterType="java.lang.Integer">
    select id,username,password,age,phone from user
    <where>
        <foreach collection="list" item="id" open="id in (" close=")" separator=",">
            #{id}
        </foreach>
    </where>
</select>

代码

@Test
public void test04(){
    ArrayList<Integer> ids = new ArrayList<Integer>();
    Collections.addAll(ids, 1, 2, 3, 4);
    List<User> users = userMapper.queryUsersByIds(ids);
    System.out.println(users);
}

6、trim

格式 pre- presay

xml 复制代码

格式 <trim prefix=前缀''   prefixoverrides=''
	        suffix=后缀''   suffixoverrides=''>

替换where

<select id="queryUserByCondition" resultType="com.linjiu.model.User" parameterType="com.linjiu.model.User">
    select id,username,password,age,phone from user
    <trim prefix="where" prefixOverrides="and">
        <if test="age!=null and age!=''">
            and age=#{age}
        </if>
        <if test="phone!=null and phone!=''">
            and phone=#{phone}
        </if>
    </trim>
</select>

替换set

<update id="updateUser" parameterType="com.linjiu.model.User">

    update user
    <trim prefix="set" suffixOverrides=",">
        <if test="password!=null and password!=''">
            password=#{password},
        </if>
        <if test="age!=null and age!=''">
            age=#{age},
        </if>
    </trim>
    where id=#{id}
</update>

7、Sql片段

格式

<sql id="别名">
    查询的所有字段
</sql>

使用的时候 <include refid="别名"/>

二、分页

1、分页的使用步骤

1.1、导入maven依赖

<!--        pageHelper依赖-->
        <dependency>
            <groupId>com.github.pagehelper</groupId>
            <artifactId>pagehelper</artifactId>
            <version>4.1.6</version>
        </dependency>
        <dependency>
            <groupId>com.github.jsqlparser</groupId>
            <artifactId>jsqlparser</artifactId>
            <version>0.9.6</version>
        </dependency>

2、mybatis配置文件中指定方言

<plugins>
    <!-- 注意：分页助手的插件  配置在通用mapper之前 -->
    <plugin interceptor="com.github.pagehelper.PageHelper">
        <!-- 指定方言 -->
        <property name="dialect" value="mysql"/>
    </plugin>
</plugins>

3、java代码测试

@Test
public void test02(){

    User user = new User();
    PageHelper.startPage(1, 3);
    List<User> users = userMapper.queryUsersByCondition(user);
    PageInfo<User> pageInfo = new PageInfo<User>(users);

    System.out.println("总条数："+pageInfo.getTotal());
    System.out.println("总页数："+pageInfo.getPages());
    System.out.println("当前页："+pageInfo.getPageNum());
    System.out.println("每页显示长度："+pageInfo.getPageSize());
    System.out.println("是否第一页："+pageInfo.isIsFirstPage());
    System.out.println("是否最后一页："+pageInfo.isIsLastPage());
    List<User> list = pageInfo.getList();
    for (User user1 : list) {
        System.out.println(user1);
    }

}

三、mybatis多表查询

1、一对一

markdown 复制代码

# 步骤
	- 建表  user 和 card
	- 创建实体类 
	- 配置文件
	- 测试

创建实体类

java 复制代码

public class Card {
    private int id;
    private String num;
    private User user;
}

CREATE TABLE card (
id int(11) NOT NULL AUTO_INCREMENT,
num varchar(20) DEFAULT NULL,
uid int(11) DEFAULT NULL,

PRIMARY KEY (id)

) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;

配置文件
<resultMap id="cards" type="com.linjiu.model.Card"> <id column="id" property="id"></id> <result column="num" property="num"></result> <association property="user" javaType="com.linjiu.model.User"> <id column="uid" property="id"></id> <result column="username" property="username"></result> <result column="password" property="password"></result> <result column="age" property="age"></result> <result column="phone" property="phone"></result> </association> </resultMap> <select id="findAllCard" resultMap="cards"> select c.id id,num,uid,username,password,age,phone from card c,user u where c.uid=u.id </select>
标签介绍

markdown 复制代码

<resultMap>：配置数据库库字段和Java对象属性的映射关系标签。
    id 属性：唯一标识
    type 属性：实体对象类型
<id>：配置主键映射关系标签。
<result>：配置非主键映射关系标签。
    column 属性：表中字段名称
    property 属性： 实体对象变量名称
<association>：配置被包含对象的映射关系标签。
    property 属性：被包含对象的变量名
    javaType 属性：被包含对象的数据类型

测试

java 复制代码

@Test
public void test05(){
    List<Card> allCard = cardMapper.findAllCard();
    System.out.println(allCard);
}

2、一对多

实体类和表 classes student

java 复制代码

package com.linjiu.model;

public class Student {

    private int id;
    private String name;
    private int age;

}

public class Classes {

    private int id;
    private String name;
    private List<Student> students;
}

CREATE TABLE classes (
id int(11) NOT NULL,
name varchar(255) DEFAULT NULL,

PRIMARY KEY (id)

) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE student (
id int(11) NOT NULL,
name varchar(255) DEFAULT NULL,
age int(11) DEFAULT NULL,
cid int(11) DEFAULT NULL,

PRIMARY KEY (id)

) ENGINE=InnoDB DEFAULT CHARSET=utf8;

配置文件
<resultMap id="class" type="com.linjiu.model.Classes"> <id column="id" property="id"></id> <result column="name" property="name"></result> <collection property="students" ofType="com.linjiu.model.Student"> <id column="sid" property="id"></id> <result column="sage" property="age"></result> <result column="sname" property="name"></result> </collection> </resultMap> <select id="findAll" resultMap="class"> select c.id id,c.name name,s.id sid,s.name sname,s.age sage from classes c,student s where s.cid=c.id </select>
标签介绍

xml 复制代码

<resultMap>：配置字段和对象属性的映射关系标签。
    id 属性：唯一标识
    type 属性：实体对象类型
<id>：配置主键映射关系标签。
<result>：配置非主键映射关系标签。
    column 属性：表中字段名称
    property 属性： 实体对象变量名称
<collection>：配置被包含集合对象的映射关系标签。
    property 属性：被包含集合对象的变量名
    ofType 属性：集合中保存的对象数据类型

3、多对多

3.1、实体类

java 复制代码

@Data
@AllArgsConstructor
@NoArgsConstructor
@Builder
public class Student {
    private int id;
    private String name;
    private int age;
    private List<Teacher> teachers;
}

java 复制代码

@Data
@AllArgsConstructor
@NoArgsConstructor
@Builder
public class Teacher {
    private int id;
    private String name;
    private String sex;
    private List<Student> students;
}

3.2、编写mapper

java 复制代码

public interface StudentMapper {

    List<Student> findAllStudent();
}

public interface StudentMapper {

    List<Student> findAllStudent();
}

3.3、mapper配置文件

xml 复制代码

<?xml version="1.0" encoding="UTF-8" ?>
<!--MyBatis的DTD约束-->
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.linjiu.dao.StudentMapper">

    <resultMap id="student" type="com.linjiu.model.Student">
        <id property="id" column="sid" />
        <result property="name" column="sname"/>
        <result property="age" column="sage"/>
        <collection property="teachers" ofType="com.linjiu.model.Teacher">
            <id property="id" column="tid" />
            <result property="name" column="tname"/>
            <result property="sex" column="tsex"/>
        </collection>
    </resultMap>

    <select id="findAllStudent" resultMap="student">
        select
            s.id sid,s.name sname,s.age sage,
            t.id tid,t.name tname,t.sex tsex
        from
            teacher t,student s,stu_teach st
        where
            t.id=st.tid and s.id=st.sid
    </select>
</mapper>

xml 复制代码

<?xml version="1.0" encoding="UTF-8" ?>
<!--MyBatis的DTD约束-->
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.linjiu.dao.TeachertMapper">

    <resultMap id="teacher" type="com.linjiu.model.Teacher">
        <id property="id" column="tid" />
        <result property="name" column="tname"/>
        <result property="sex" column="tsex"/>
        <collection property="students" ofType="com.linjiu.model.Student">
            <id property="id" column="sid" />
            <result property="name" column="sname"/>
            <result property="age" column="sage"/>
        </collection>
    </resultMap>

    <select id="findAllTeacher" resultMap="teacher">
        select
            t.id tid,t.name tname,t.sex tsex,
            s.id sid,s.name sname,s.age sage
        from
            teacher t,student s,stu_teach st
        where
            t.id=st.tid and s.id=st.sid
    </select>
</mapper>

3.4、测试

java 复制代码

@Autowired
private StudentMapper studentMapper;

@Autowired
private TeachertMapper teachertMapper;

@Test
public void test06(){
    List<Student> allStudent = studentMapper.findAllStudent();
    for (Student student : allStudent) {
        String name = student.getName();
        System.out.println(name);
        for (Teacher teacher : student.getTeachers()) {
            System.out.print("\t"+teacher.getName()+"-"+teacher.getSex()+"\t");
        }
        System.out.println();
    }
}