之前我们介绍了if,where标签的使用;本篇我们需要在if,where标签的基础上介绍如何使用Mybatis提供的choose标签动态生成条件语句。
如果您对if,where标签动态生成条件语句不太了解,建议您先进行了解后再阅读本篇,可以参考:
Mybatis 动态SQL -- 使用if,where标签动态生成条件语句https://blog.csdn.net/m1729339749/article/details/132627894
一、数据准备
这里我们直接使用脚本初始化数据库中的数据
sql
-- 如果数据库不存在则创建数据库
CREATE DATABASE IF NOT EXISTS demo DEFAULT CHARSET utf8;
-- 切换数据库
USE demo;
-- 创建用户表
CREATE TABLE IF NOT EXISTS T_TEACHER(
ID INT PRIMARY KEY COMMENT '教师编号',
TEACHER_NAME VARCHAR(64) NOT NULL COMMENT '教师名称',
DEPARTMENT VARCHAR(16) NOT NULL COMMENT '所属部门',
BIRTH DATE NOT NULL COMMENT '出生年月',
DEGREE VARCHAR(16) NOT NULL COMMENT '学历(ZK:专科, BK:本科, YJS:研究生, BS:博士)'
);
-- 插入用户数据
INSERT INTO T_TEACHER(ID, TEACHER_NAME, DEPARTMENT, BIRTH, DEGREE)
VALUES(1, '张三1', '001', '1990-06-12', 'BK'),
(2, '李四1', '002', '1992-05-10', 'BK'),
(3, '张三2', '003', '1988-01-15', 'YJS'),
(4, '李四2', '001', '1979-03-10', 'BK'),
(5, '李四3', '003', '1995-08-16', 'YJS');
创建了一个名称为demo的数据库;并在库里创建了名称为T_TEACHER的教师表并向表中插入了数据
二、环境搭建
1、创建实体类
在cn.horse.demo下创建TeacherInfo实体类:
TeacherInfo 类:
java
package cn.horse.demo;
import java.time.LocalDate;
public class TeacherInfo {
private Integer id;
private String name;
private String department;
private LocalDate birth;
private String degree;
@Override
public String toString() {
StringBuilder stringBuilder = new StringBuilder();
stringBuilder.append("{ ");
stringBuilder.append("id: ");
stringBuilder.append(this.id);
stringBuilder.append(", ");
stringBuilder.append("name: ");
stringBuilder.append(this.name);
stringBuilder.append(", ");
stringBuilder.append("department: ");
stringBuilder.append(this.department);
stringBuilder.append(", ");
stringBuilder.append("birth: ");
stringBuilder.append(this.birth);
stringBuilder.append(", ");
stringBuilder.append("degree: ");
stringBuilder.append(this.degree);
stringBuilder.append(" }");
return stringBuilder.toString();
}
}
2、Mapper配置文件
在resources的目录下新建TeacherInfoMapper.xml配置文件
XML
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="cn.horse.demo.TeacherInfoMapper">
<select id="findAll" parameterType="cn.horse.demo.TeacherInfoQuery" resultType="cn.horse.demo.TeacherInfo">
SELECT
ID,
TEACHER_NAME name,
DEPARTMENT,
BIRTH,
DEGREE
FROM T_TEACHER
<where>
<if test="null != id and '' != id">
AND ID = #{id}
</if>
<if test="null != name and '' != name">
AND TEACHER_NAME = #{name}
</if>
<if test="null != department and '' != department">
AND DEPARTMENT = #{department}
</if>
<if test="null != degree and '' != degree">
AND DEGREE = #{degree}
</if>
</where>
</select>
</mapper>
3、引入配置文件
在resources下新建mybatis-config.xml配置文件,并引入TeacherInfoMapper.xml配置文件
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>
<settings>
<setting name="logImpl" value="JDK_LOGGING"/>
</settings>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="org.gjt.mm.mysql.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/demo?useUnicode=true&useSSL=false&characterEncoding=utf8"/>
<property name="username" value="root"/>
<property name="password" value="horse"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="demo/TeacherInfoMapper.xml" />
</mappers>
</configuration>
4、会话工具类
在cn.horse.demo包下新建SqlSessionUtils工具类
java
package cn.horse.demo;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.InputStream;
import java.util.Objects;
public class SqlSessionUtils {
private static final SqlSessionFactory sqlSessionFactory;
static {
// 读取mybatis配置文件
InputStream inputStream = ClassLoader.getSystemClassLoader().getResourceAsStream("mybatis-config.xml");
// 根据配置创建SqlSession工厂
sqlSessionFactory = new SqlSessionFactoryBuilder()
.build(inputStream);
}
/**
* 开启会话
* @return
*/
public static SqlSession openSession() {
return sqlSessionFactory.openSession();
}
/**
* 关闭会话
* @param sqlSession
*/
public static void closeSession(SqlSession sqlSession) {
if(Objects.nonNull(sqlSession)) {
sqlSession.close();
}
}
}
5、JDK 日志系统配置
在resources的目录下新建logging.properties配置文件
bash
handlers=java.util.logging.ConsoleHandler
.level=INFO
cn.horse.demo.TeacherInfoMapper.level=FINER
java.util.logging.ConsoleHandler.level=ALL
java.util.logging.ConsoleHandler.formatter=java.util.logging.SimpleFormatter
java.util.logging.SimpleFormatter.format=%1$tY-%1$tm-%1$td %1$tT.%1$tL %4$s %3$s - %5$s%6$s%n
在cn.horse.demo下新建JdkLogConfig类:
JdkLogConfig 类:
java
package cn.horse.demo;
import java.io.IOException;
import java.io.InputStream;
import java.util.logging.LogManager;
public class JdkLogConfig {
public JdkLogConfig() {
try {
InputStream inputStream = ClassLoader.getSystemClassLoader().getResourceAsStream("logging.properties");
LogManager.getLogManager().readConfiguration(inputStream);
} catch (IOException e) {
throw new RuntimeException(e);
}
}
}
6、启动程序
java
package cn.horse.demo;
import org.apache.ibatis.session.SqlSession;
import java.util.List;
public class Main {
public static void main(String[] args) {
// 引入JDK日志配置
System.setProperty("java.util.logging.config.class", "cn.horse.demo.JdkLogConfig");
TeacherInfoQuery teacherInfoQuery = new TeacherInfoQuery();
teacherInfoQuery.setId(1);
teacherInfoQuery.setName("张三1");
teacherInfoQuery.setDepartment("001");
teacherInfoQuery.setDegree("BK");
findAll("cn.horse.demo.TeacherInfoMapper.findAll", teacherInfoQuery);
}
private static void findAll(String statement, TeacherInfoQuery teacherInfoQuery) {
SqlSession sqlSession = null;
try {
sqlSession = SqlSessionUtils.openSession();
List<TeacherInfo> teacherInfoList = sqlSession.selectList(statement, teacherInfoQuery);
for (TeacherInfo teacherInfo: teacherInfoList) {
System.out.println(teacherInfo);
}
} finally {
SqlSessionUtils.closeSession(sqlSession);
}
}
}
执行后的结果如下:
三、choose标签的使用
在上面的运行结果中,我们可以看到执行的SQL语句:
sql
SELECT ID, TEACHER_NAME name, DEPARTMENT, BIRTH, DEGREE FROM T_TEACHER WHERE ID = ? AND TEACHER_NAME = ? AND DEPARTMENT = ? AND DEGREE = ?
从SQL中我们可以看到条件语句中包含了ID、TEACHER_NAME、DEPARTMENT、DEGREE;而在实际的场景中ID是唯一的,ID作为条件时,其他的条件就显得比较多余,显然上面动态生成的条件语句是存在一些问题的,下面我们使用choose标签来解决此类问题:
XML
<select id="findAll" parameterType="cn.horse.demo.TeacherInfoQuery" resultType="cn.horse.demo.TeacherInfo">
SELECT
ID,
TEACHER_NAME name,
DEPARTMENT,
BIRTH,
DEGREE
FROM T_TEACHER
<where>
<choose>
<when test="null != id and '' != id">
AND ID = #{id}
</when>
<otherwise>
<if test="null != name and '' != name">
AND TEACHER_NAME = #{name}
</if>
<if test="null != department and '' != department">
AND DEPARTMENT = #{department}
</if>
<if test="null != degree and '' != degree">
AND DEGREE = #{degree}
</if>
</otherwise>
</choose>
</where>
</select>
choose 标签: 标签中可以包含多个when标签、一个otherwise标签
when 标签: test属性值用作条件判断,与if标签的test属性一样;when标签可以多次使用
otherwise 标签: otherwise标签最多只能使用一次,并且只能作为choose标签内的最后一个标签。
choose 标签类似于Java中的switch语句,会依次判断when标签中的条件是否满足,直到找到满足条件的when标签,并将when标签中的条件语句拼装到SQL语句中并跳出choose标签;如果找不到满足条件的when标签,则将otherwise标签中的条件语句拼装到SQL语句中并跳出choose标签;
1、示例:使用ID查询教师
java
// 引入JDK日志配置
System.setProperty("java.util.logging.config.class", "cn.horse.demo.JdkLogConfig");
TeacherInfoQuery teacherInfoQuery = new TeacherInfoQuery();
teacherInfoQuery.setId(1);
teacherInfoQuery.setName("张三1");
teacherInfoQuery.setDepartment("001");
teacherInfoQuery.setDegree("BK");
findAll("cn.horse.demo.TeacherInfoMapper.findAll", teacherInfoQuery);
执行后的结果如下:
结果分析:
choose标签中,先判断第一个when标签条件是否满足,因为id为1,第一个条件满足,则将条件AND ID = #{id} 拼装到SQL语句中并跳出choose标签;所以执行的条件语句中只有ID = ? 条件
2、示例:使用名称查询教师
java
// 引入JDK日志配置
System.setProperty("java.util.logging.config.class", "cn.horse.demo.JdkLogConfig");
TeacherInfoQuery teacherInfoQuery = new TeacherInfoQuery();
teacherInfoQuery.setName("张三1");
findAll("cn.horse.demo.TeacherInfoMapper.findAll", teacherInfoQuery);
执行后的结果如下:
结果分析:
choose标签中,先判断第一个when标签条件是否满足,因为id为null,第一个条件不满足,没有找到满足条件的when标签,则将otherwise标签中的条件语句拼装到SQL语句中并跳出choose标签(由于这里otherwise标签中的条件语句是动态SQL语句,则会执行动态SQL语句,执行后的结果AND TEACHER_NAME = #{name} 作为otherwise标签的内容);所以执行的条件语句中只有TEACHER_NAME = ? 条件