簡介
MyBatis 中動態(tài)語句 choose-when-otherwise 類似于 Java 中的 switch-case-default 語句。由于 MyBatis 并沒有為 if 提供對應(yīng)的 else 標(biāo)簽，如果想要達(dá)到…… 的效果，可以借助 、、 來實現(xiàn)。
語法
<choose>
<when test="判斷條件1">
SQL語句1
</when >
<when test="判斷條件2">
SQL語句2
</when >
<when test="判斷條件3">
SQL語句3
</when >
<otherwise>
SQL語句4
</otherwise>
</choose>
hoose 標(biāo)簽按順序判斷其內(nèi)部 when 標(biāo)簽中的判斷條件是否成立，如果有一個成立，則執(zhí)行相應(yīng)的 SQL 語句，choose 執(zhí)行結(jié)束；如果都不成立，則執(zhí)行 otherwise 中的 SQL 語句。這類似于 Java 的 switch 語句，choose 為 switch，when 為 case，otherwise 則為 default。
場景示例
MyBatis 就會根據(jù)參數(shù)的設(shè)置進(jìn)行判斷來動態(tài)組裝 SQL
以下示例要求：
- 當(dāng)網(wǎng)站名稱不為空時，只用網(wǎng)站名稱作為條件進(jìn)行模糊查詢；
- 當(dāng)網(wǎng)站名稱為空，而網(wǎng)址不為空時，則用網(wǎng)址作為條件進(jìn)行模糊查詢；
- 當(dāng)網(wǎng)站名稱和網(wǎng)址都為空時，則要求網(wǎng)站年齡不為空。
<mapper namespace="net.biancheng.mapper.WebsiteMapper">
<select id="selectWebsite"
parameterType="net.biancheng.po.Website"
resultType="net.biancheng.po.Website">
SELECT id,name,url,age,country
FROM website WHERE 1=1
<choose>
<when test="name != null and name !=''">
AND name LIKE CONCAT('%',#{name},'%')
</when>
<when test="url != null and url !=''">
AND url LIKE CONCAT('%',#{url},'%')
</when>
<otherwise>
AND age is not null
</otherwise>
</choose>
</select>
</mapper>
choose-when-otherwise標(biāo)簽-完整案例
1.數(shù)據(jù)庫準(zhǔn)備
# 創(chuàng)建一個名稱為t_customer的表
CREATE TABLE t_customer (
id int(32) PRIMARY KEY AUTO_INCREMENT,
username varchar(50),
jobs varchar(50),
phone varchar(16)
);
# 插入3條數(shù)據(jù)
INSERT INTO t_customer VALUES ('1', 'joy', 'teacher', '13733333333');
INSERT INTO t_customer VALUES ('2', 'jack', 'teacher', '13522222222');
INSERT INTO t_customer VALUES ('3', 'tom', 'worker', '15111111111');
2.新建項目或Module
3 pom.xml中添加
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<parent>
<artifactId>mybatis</artifactId>
<groupId>com.example</groupId>
<version>1.0-SNAPSHOT</version>
</parent>
<modelVersion>4.0.0</modelVersion>
<groupId>com.biem</groupId>
<artifactId>dynamaicSql</artifactId>
<properties>
<maven.compiler.source>8</maven.compiler.source>
<maven.compiler.target>8</maven.compiler.target>
</properties>
<dependencies>
<!--1.引入mybatis包-->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.4.6</version>
</dependency>
<!--2.單元測試-->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
<scope>test</scope>
</dependency>
<!--3.mysql驅(qū)動-->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.18</version>
<scope>runtime</scope>
</dependency>
<!--4.log4j日志-->
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.18.16</version>
</dependency>
</dependencies>
</project>
4.創(chuàng)建package和文件夾
src/main/java/下創(chuàng)建package
com.biem.pojo
com.biem.mapper
com.biem.util
src/main/resources/下創(chuàng)建文件夾
com/biem/mapper
src/test/java下創(chuàng)建package
com.biem.test
5 框架配置文件
5.1 mybatis核心配置文件mybatis-config.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>
<!--引入properties文件-->
<properties resource="jdbc.properties"></properties>
<!--將下劃線映射為駝峰-->
<settings>
<setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>
<!--設(shè)置類型別名-->
<typeAliases>
<!--
以包為單位，將包下所有的類型設(shè)置設(shè)置默認(rèn)的類型別名，即類名且不區(qū)分大小寫
-->
<package name="com.biem.pojo"/>
</typeAliases>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driver}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
</dataSource>
</environment>
</environments>
<!-- 引入映射文件 -->
<mappers>
<!--
以包為單位引入映射文件
要求：
1. mapper接口所在的包要和映射文件所在的包一致
2. mapper接口要和映射文件的名字一致
-->
<package name="com.biem.mapper"/>
</mappers>
</configuration>
5.2 mybatis屬性文件jdbc.properties
jdbc.driver=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/mybatis?serverTimezone=UTC
jdbc.username=root
jdbc.password=root
5.3 log4j.xml文件
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
<appender name="STDOUT" class="org.apache.log4j.ConsoleAppender">
<param name="Encoding" value="UTF-8"/>
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%-5p %d{MM-dd HH:mm:ss,SSS} %m (%F:%L) \n"/>
</layout>
</appender>
<logger name="java.sql">
<level value="debug"/>
</logger>
<logger name="org.apache.ibatis">
<level value="info"/>
</logger>
<root>
<level value="debug"/>
<appender-ref ref="STDOUT"/>
</root>
</log4j:configuration>
6 用戶配置文件
6.1 實體類
package com.biem.pojo;
import lombok.*;
/**
* ClassName: Customer
* Package: com.biem.pojo
* Description:
*
* @Create 2023/4/5 22:17
* @Version 1.0
*/
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@Builder
@ToString
public class Customer {
private Integer id;
private String username;
private String jobs;
private String phone;
}
需要在pom.xml中引入lombok，簡化原來的實體類的代碼
6.2 mybatis接口類
package com.biem.mapper;
/**
* ClassName: CustomerMapper
* Package: com.biem.mapper
* Description:
*
* @Create 2023/4/5 22:19
* @Version 1.0
*/
public interface CustomerMapper {
}
6.3 mybatis用戶配置文件
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.biem.mapper.CustomerMapper">
<!-- namespace要和mapper接口的全類名保持一致，例如com.biem.mybatis.mapper.xxxMapper -->
<!-- sql語句要和接口的方法名保持一致 -->
</mapper>
6.4 mybatis工具類
package com.biem.util;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.IOException;
import java.io.InputStream;
/**
* ClassName: MybatisUtil
* Package: com.biem.utils
* Description:
*
* @Create 2023/4/5 22:23
* @Version 1.0
*/
public class MybatisUtil {
//利用static(靜態(tài))屬于類不屬于對象,且全局唯一
private static SqlSessionFactory sqlSessionFactory = null;
//利用靜態(tài)塊在初始化類時實例化sqlSessionFactory
static {
InputStream is= null;
try {
is = Resources.getResourceAsStream("mybatis-config.xml");
sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
} catch (IOException e) {
e.printStackTrace();
throw new ExceptionInInitializerError(e);
}
}
/**
* openSession 創(chuàng)建一個新的SqlSession對象
* @return SqlSession對象
*/
public static SqlSession openSession(boolean autoCommit){
return sqlSessionFactory.openSession(autoCommit);
}
public static SqlSession openSession(){
return sqlSessionFactory.openSession();
}
/**
* 釋放一個有效的SqlSession對象
* @param session 準(zhǔn)備釋放SqlSession對象
*/
public static void closeSession(SqlSession session){
if(session != null){
session.close();
}
}
}
項目結(jié)構(gòu)如下
7 標(biāo)簽功能測試
在使用if標(biāo)簽時，只要test屬性中的表達(dá)式為true，就會執(zhí)行元素中的條件語句，但是在實際情況下有時只需要從多個選項中選擇一個去執(zhí)行，比如下面的場景：
當(dāng)查詢數(shù)據(jù)庫t_customer時，
客戶姓名不為空，則只根據(jù)客戶名稱進(jìn)行客戶篩選，
當(dāng)客戶名稱為null的時候，可客戶職業(yè)不為空，則根據(jù)客戶職業(yè)進(jìn)行篩選，
當(dāng)客戶名稱和客戶職業(yè)都為空的時候，要求查詢電話不為空的客戶文章來源：http://www.zghlxwxcb.cn/news/detail-700824.html
7.1 com.biem.mapper.CustomerMapper.class中添加
public List<Customer> findCustomerByCondition(Customer customer);
7.2 com/biem/mapper/CustomerMapper.xml中添加
<!-- public List<Customer> findCustomerByCondition(Customer customer);-->
<select id="findCustomerByCondition" parameterType="customer" resultType="customer">
select * from t_customer where 1=1
<!--條件判斷-->
<choose>
<when test="username!=null and username!=''">
and username like concat('%',#{username},'%')
</when>
<when test="jobs!=null and jobs!=''">
and jobs=#{jobs}
</when>
<otherwise>
and phone is not null
</otherwise>
</choose>
</select>
8 功能測試
在src/test/java中創(chuàng)建類com.biem.test.TestCustomer.java，內(nèi)容如下文章來源地址http://www.zghlxwxcb.cn/news/detail-700824.html
package com.biem.test;
import com.biem.mapper.CustomerMapper;
import com.biem.pojo.Customer;
import com.biem.util.MybatisUtil;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.List;
/**
* ClassName: TestCustomer
* Package: com.biem.test
* Description:
*
* @Create 2023/4/5 22:32
* @Version 1.0
*/
public class TestCustomer {
@Test
public void testFindAll(){
// 通過工具類獲取SqlSession對象
SqlSession session = MybatisUtil.openSession();
// 創(chuàng)建Customer對象，封裝需要組合查詢的條件
Customer customer = new Customer();
CustomerMapper mapper = session.getMapper(CustomerMapper.class);
List<Customer> customers = mapper.findCustomerByCondition(customer);
System.out.println("customers = " + customers);
// 關(guān)閉SqlSession
session.close();
}
@Test
public void testFindCustomerByName(){
// 通過工具類獲取SqlSession對象
SqlSession session = MybatisUtil.openSession();
// 創(chuàng)建Customer對象，封裝需要組合查詢的條件
Customer customer = new Customer();
customer.setUsername("jack");
CustomerMapper mapper = session.getMapper(CustomerMapper.class);
List<Customer> customers = mapper.findCustomerByCondition(customer);
System.out.println("customers = " + customers);
// 關(guān)閉SqlSession
session.close();
}
@Test
public void testFindCustomerByJobs(){
// 通過工具類獲取SqlSession對象
SqlSession session = MybatisUtil.openSession();
// 創(chuàng)建Customer對象，封裝需要組合查詢的條件
Customer customer = new Customer();
customer.setJobs("teacher");
CustomerMapper mapper = session.getMapper(CustomerMapper.class);
List<Customer> customers = mapper.findCustomerByCondition(customer);
System.out.println("customers = " + customers);
// 關(guān)閉SqlSession
session.close();
}
@Test
public void testFindCustomerByPhone(){
// 通過工具類獲取SqlSession對象
SqlSession session = MybatisUtil.openSession();
// 創(chuàng)建Customer對象，封裝需要組合查詢的條件
Customer customer = new Customer();
customer.setPhone("1");
CustomerMapper mapper = session.getMapper(CustomerMapper.class);
List<Customer> customers = mapper.findCustomerByCondition(customer);
System.out.println("customers = " + customers);
// 關(guān)閉SqlSession
session.close();
}
}
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