MyBatis-Plus 条件构造器之condition参数

灰太狼 2022-12-13 04:16 118阅读 0赞

推荐：[MyBatis Plus汇总][MyBatis Plus]

## MyBatis-Plus 条件构造器之condition参数 ##

首先创建一个数据库表，如下图所示：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3OTYwNjAz_size_16_color_FFFFFF_t_70]

然后创建一个Spring Boot项目，pom.xml和配置如下：

<?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">
        <modelVersion>4.0.0</modelVersion>
    
        <groupId>org.kaven</groupId>
        <artifactId>mybatis-plus</artifactId>
        <version>1.0-SNAPSHOT</version>
    
        <parent>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-parent</artifactId>
            <version>2.3.4.RELEASE</version>
            <relativePath/>
        </parent>
    
        <properties>
            <java.version>1.8</java.version>
        </properties>
    
        <dependencies>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter</artifactId>
            </dependency>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-test</artifactId>
            </dependency>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-webflux</artifactId>
            </dependency>
            <dependency>
                <groupId>com.baomidou</groupId>
                <artifactId>mybatis-plus-boot-starter</artifactId>
                <version>3.4.0</version>
            </dependency>
            <dependency>
                <groupId>mysql</groupId>
                <artifactId>mysql-connector-java</artifactId>
                <version>5.1.49</version>
            </dependency>
            <dependency>
                <groupId>org.projectlombok</groupId>
                <artifactId>lombok</artifactId>
            </dependency>
        </dependencies>
    
        <build>
            <plugins>
                <plugin>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-maven-plugin</artifactId>
                </plugin>
            </plugins>
        </build>
    </project>

spring:
      application:
        name: mybatis-plus
      datasource:
        driver-class-name: com.mysql.jdbc.Driver
        username: root
        password: ITkaven@123
        url: jdbc:mysql://127.0.0.1:3306/test?characterEncoding=utf-8&useSSL=false
    
    server:
      port: 8085
    
    logging:
      level:
        root: warn
        com.kaven.mybatisplus.dao: trace
      pattern:
        console: '%p%m%n'
    
    mybatis-plus:
      mapper-locations: classpath:mappers/*.xml

实体类User：

package com.kaven.mybatisplus.entity;
    
    import com.baomidou.mybatisplus.annotation.TableField;
    import com.baomidou.mybatisplus.annotation.TableId;
    import com.baomidou.mybatisplus.annotation.TableName;
    import lombok.Data;
    
    @TableName("user")
    @Data
    public class User { 
    
        @TableId
        private String id;
    
        @TableField("username")
        private String username;
    
        @TableField("password")
        private String password;
    
        @TableField("age")
        private Integer age;
    
        /** * 使用 @TableField(exist = false) ，表示该字段在数据库中不存在 ，所以不会插入数据库中 * 使用 transient 、 static 修饰属性也不会插入数据库中 */
        @TableField(exist = false)
        private String phone;
    }

Mapper接口UserMapper：

package com.kaven.mybatisplus.dao;
    
    import com.baomidou.mybatisplus.core.mapper.BaseMapper;
    import com.kaven.mybatisplus.entity.User;
    import org.springframework.stereotype.Component;
    
    
    @Component
    public interface UserMapper extends BaseMapper<User> { }

启动类：

package com.kaven.mybatisplus;
    
    import org.mybatis.spring.annotation.MapperScan;
    import org.springframework.boot.SpringApplication;
    import org.springframework.boot.autoconfigure.SpringBootApplication;
    
    @SpringBootApplication
    @MapperScan(basePackages = "com.kaven.mybatisplus.dao")
    public class AppRun { 
        public static void main(String[] args) { 
            SpringApplication.run(AppRun.class , args);
        }
    }

`@MapperScan(basePackages = "com.kaven.mybatisplus.dao")`这个一定要加上。

我们先在数据库中添加几行数据，方便演示。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3OTYwNjAz_size_16_color_FFFFFF_t_70 1]  
我之前介绍的条件构造器都没有使用过`condition`参数。从`AbstractWrapper<T, String, QueryWrapper<T>>`的源码可以看到很多方法都有`condition`参数，它是一个布尔型的参数，意思就是是否将该`sql`语句（像`in()`、`like()`）加在总`sql`语句上，如下图所示。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3OTYwNjAz_size_16_color_FFFFFF_t_70_pic_center]

首先我们自己来实现一个和`condition`参数一样功能的方法。

*  查询`username`包含字符`k`，并且`age`属于\[22 , 40 , 30 \]。

package com.kaven.mybatisplus.dao;
    
    import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
    import com.kaven.mybatisplus.entity.User;
    import org.junit.Test;
    import org.junit.runner.RunWith;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.boot.test.context.SpringBootTest;
    import org.springframework.test.context.junit4.SpringRunner;
    import org.springframework.util.CollectionUtils;
    import org.springframework.util.StringUtils;
    
    import java.util.Arrays;
    import java.util.List;
    
    
    @RunWith(SpringRunner.class)
    @SpringBootTest
    public class UserMapperConditionTest { 
    
        @Autowired
        private UserMapper userMapper;
    
        @Test
        public void selectList(){ 
           String username = "k";
           List<Integer> ageList = Arrays.asList(22 , 40 , 30);
           List<User> userList = userMapper.selectList(condition(username , ageList));
           userList.forEach(System.out::println);
        }
    
        public QueryWrapper<User> condition(String username , List<Integer> ageList){ 
            QueryWrapper<User> userQueryWrapper = new QueryWrapper<>();
            if(!StringUtils.isEmpty(username)){ 
                userQueryWrapper.like("username" , username);
            }
            if(!CollectionUtils.isEmpty(ageList)){ 
                userQueryWrapper.in("age" , ageList);
            }
            return userQueryWrapper;
        }
    }

结果如下：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3OTYwNjAz_size_16_color_FFFFFF_t_70 2]  
结果是正确的。

我们使用`condition`参数来实现一下。

package com.kaven.mybatisplus.dao;
    
    import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
    import com.kaven.mybatisplus.entity.User;
    import org.junit.Test;
    import org.junit.runner.RunWith;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.boot.test.context.SpringBootTest;
    import org.springframework.test.context.junit4.SpringRunner;
    import org.springframework.util.CollectionUtils;
    import org.springframework.util.StringUtils;
    
    import java.util.Arrays;
    import java.util.List;
    
    
    @RunWith(SpringRunner.class)
    @SpringBootTest
    public class UserMapperConditionTest { 
    
        @Autowired
        private UserMapper userMapper;
    
        @Test
        public void selectList(){ 
           String username = "k";
           List<Integer> ageList = Arrays.asList(22 , 40 , 30);
           List<User> userList = userMapper.selectList(condition(username , ageList));
           userList.forEach(System.out::println);
        }
    
        public QueryWrapper<User> condition(String username , List<Integer> ageList){ 
            QueryWrapper<User> userQueryWrapper = new QueryWrapper<>();
    // if(!StringUtils.isEmpty(username)){ 
    // userQueryWrapper.like("username" , username);
    // }
    // if(!CollectionUtils.isEmpty(ageList)){ 
    // userQueryWrapper.in("age" , ageList);
    // }
            userQueryWrapper.like(!StringUtils.isEmpty(username) , "username" , username)
                            .in(!CollectionUtils.isEmpty(ageList) , "age" , ageList);
            return userQueryWrapper;
        }
    }

结果如下：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3OTYwNjAz_size_16_color_FFFFFF_t_70 3]  
结果也是正确的。

写博客是博主记录自己的学习过程，如果有错误，请指正，谢谢！

[MyBatis Plus]: https://kaven.blog.csdn.net/article/details/108982474
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