if标签简介
if标签:条件判断
MyBatis if 类似于 Java 中的 if 语句,是 MyBatis 中最常用的判断语句。使用 if 标签可以节省许多拼接 SQL 的工作,把精力集中在 XML 的维护上。
if 语句使用方法简单,常常与 test 属性联合使用。语法如下:
if标签语法结构
<if test="判断条件">
SQL语句
</if>
if标签使用场景
最常见的场景是在 if 语句中包含 where 子句
<select id="selectAllWebsite" resultMap="myResult">
select id,name,url from website
<if test="name != null">
where name like #{name}
</if>
</select>
以上代表表示根据网站名称去查找相应的网站信息,但是网站名称是一个可填可不填的条件,不填写的时候不作为查询条件。
可多个 if 语句同时使用。以下语句表示为可以按照网站名称(name)或者网址(url)进行模糊查询。如果您不输入名称或网址,则返回所有的网站记录。但是,如果你传递了任意一个参数,它就会返回与给定参数相匹配的记录:
<select id="selectAllWebsite" resultMap="myResult">
select id,name,url from website where 1=1
<if test="name != null">
AND name like #{name}
</if>
<if test="url!= null">
AND url like #{url}
</if>
</select>
DROP TABLE IF EXISTS `website`;
CREATE TABLE `website` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(20) COLLATE utf8_unicode_ci NOT NULL,
`url` varchar(30) COLLATE utf8_unicode_ci DEFAULT '',
`age` tinyint(3) unsigned NOT NULL,
`country` char(3) COLLATE utf8_unicode_ci NOT NULL DEFAULT '',
`createtime` timestamp NULL DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
if标签案例
1.数据库准备
use mybatis;
# 创建一个名称为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条数据
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.新建项目或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>if</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.单元测试-->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
<scope>test</scope>
</dependency>
<!--3.mysql驱动-->
<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.创建package和文件夹
src/main/java/下创建package
com.biem.pojo
com.biem.mapper
com.biem.utils
src/main/resources/下创建文件夹
com/biem/mapper
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>
<!--将下划线映射为驼峰-->
<settings>
<setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>
<!--设置类型别名-->
<typeAliases>
<!--
以包为单位,将包下所有的类型设置设置默认的类型别名,即类名且不区分大小写
-->
<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>
<!--
以包为单位引入映射文件
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属性文件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 用户配置文件
6.1 实体类
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,简化原来的实体类的代码
6.2 mybatis接口类
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用户配置文件
<?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接口的全类名保持一致,例如com.biem.mybatis.mapper.xxxMapper -->
<!-- sql语句要和接口的方法名保持一致 -->
</mapper>
6.4 mybatis工具类
package com.biem.utils;
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(静态)属于类不属于对象,且全局唯一
private static SqlSessionFactory sqlSessionFactory = null;
//利用静态块在初始化类时实例化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 创建一个新的SqlSession对象
* @return SqlSession对象
*/
public static SqlSession openSession(boolean autoCommit){
return sqlSessionFactory.openSession(autoCommit);
}
public static SqlSession openSession(){
return sqlSessionFactory.openSession();
}
/**
* 释放一个有效的SqlSession对象
* @param session 准备释放SqlSession对象
*/
public static void closeSession(SqlSession session){
if(session != null){
session.close();
}
}
}
7 If标签功能测试
7.1 com.biem.mapper.CustomerMapper.class中添加
public List<Customer> findCustomerByNameAndJobs(Customer customer);
7.2 com/biem/mapper/CustomerMapper.xml中添加
<select id="findCustomerByNameAndJobs" parameterType="customer" resultType="customer">
select * from t_customer where 1=1
<if test="username !=null and username != ''">
and username like concat('%', #{username}, '%')
</if>
<if test="jobs !=null and jobs != ''">
and jobs=#{jobs}
</if>
</select>
8 功能测试
在src/test/java中创建类com.biem.test.TestCustomer.java,内容如下
package com.biem.test;
import com.biem.mapper.CustomerMapper;
import com.biem.pojo.Customer;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import com.biem.utils.MybatisUtil;
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(){
// 通过工具类获取SqlSession对象
SqlSession session = MybatisUtil.openSession();
// 创建Customer对象,封装需要组合查询的条件
Customer customer = new Customer();
CustomerMapper mapper = session.getMapper(CustomerMapper.class);
List<Customer> customers = mapper.findCustomerByNameAndJobs(customer);
System.out.println("customers = " + customers);
// 关闭SqlSession
session.close();
}
@Test
public void testFindCustomerByNameAndJobs(){
// 通过工具类获取SqlSession对象
SqlSession session = MybatisUtil.openSession();
// 创建Customer对象,封装需要组合查询的条件
Customer customer = new Customer();
customer.setUsername("jack");
customer.setJobs("teacher");
CustomerMapper mapper = session.getMapper(CustomerMapper.class);
List<Customer> customers = mapper.findCustomerByNameAndJobs(customer);
System.out.println("customers = " + customers);
// 关闭SqlSession
session.close();
}
}