MyBatis動態(tài)SQL之＜choose＞＜when＞＜otherwise＞標簽的使用

更新時間：2023年09月12日 09:59:07 作者：yandao

MyBatis中動態(tài)語句choose-when-otherwise 類似于Java中的switch-case-default語句,本文就來介紹一下MyBatis動態(tài)SQL之＜choose＞＜when＞＜otherwise＞標簽的使用,感興趣的可以了解一下

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 標簽，如果想要達到…… 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 標簽按順序判斷其內(nèi)部 when 標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)置進行判斷來動態(tài)組裝 SQL

以下示例要求：

當網(wǎng)站名稱不為空時，只用網(wǎng)站名稱作為條件進行模糊查詢；
當網(wǎng)站名稱為空，而網(wǎng)址不為空時，則用網(wǎng)址作為條件進行模糊查詢；
當網(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標簽-完整案例

1.數(shù)據(jù)庫準備

# 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 標簽功能測試

在使用if標簽時，只要test屬性中的表達式為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)客戶名稱進行客戶篩選，
當客戶名稱為null的時候，可客戶職業(yè)不為空，則根據(jù)客戶職業(yè)進行篩選，
當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

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

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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