Mybatis返回Xml返回值有resultType和resultMap,我们一般都该如何选择呢?
一、resultType
1、resultType介绍
当使用resultType做SQL语句返回结果类型处理时,对于SQL语句查询出的字段在相应的pojo中必须有和它相同的字段对应,而resultType中的内容就是pojo在本项目中的位置。
2、映射规则
- 基本类型 :resultType=基本类型
- List类型: resultType=List中元素的类型
- Map类型 单条记录:resultType =map 多条记录:resultType =Map中value的类型
3、自动映射注意事项
- 前提:SQL列名和JavaBean的属性是一致的;
- 使用resultType,如用简写需要配置typeAliases (别名);
- 如果列名和JavaBean不一致,但列名符合单词下划线分割,Java是驼峰命名法,则mapUnderscoreToCamelCase可设置为true;
4、代码演示
1、t_user_test.sql准备
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CREATE TABLE `t_user_test` ( `id` int (20) NOT NULL AUTO_INCREMENT, `user_name` varchar (60) DEFAULT NULL COMMENT '用户名称' , `real_name` varchar (60) DEFAULT NULL COMMENT '真实名称' , `sex` tinyint(3) DEFAULT NULL COMMENT '姓名' , `mobile` varchar (20) DEFAULT NULL COMMENT '电话' , `email` varchar (60) DEFAULT NULL COMMENT '邮箱' , `note` varchar (200) DEFAULT NULL COMMENT '备注' , PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=142 DEFAULT CHARSET=utf8;码 |
2、实体类
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package com.enjoylearning.mybatis.entity; import java.io.Serializable; import java.util.List; import org.apache.ibatis.annotations.Param; import com.mysql.jdbc.Blob; public class TUser implements Serializable{ private Integer id; private String userName; private String realName; private Byte sex; private String mobile; private String email; private String note; private TPosition position; private List<TJobHistory> jobs ; private List<HealthReport> healthReports; private List<TRole> roles; @Override public String toString() { String positionId= (position == null ? "" : String.valueOf(position.getId())); return "TUser [id=" + id + ", userName=" + userName + ", realName=" + realName + ", sex=" + sex + ", mobile=" + mobile + ", email=" + email + ", note=" + note + ", positionId=" + positionId + "]" ; } public Integer getId() { return id; } public void setId(Integer id) { this .id = id; } public String getUserName() { return userName; } public void setUserName(String userName) { this .userName = userName; } public String getRealName() { return realName; } public void setRealName(String realName) { this .realName = realName; } public Byte getSex() { return sex; } public void setSex(Byte sex) { this .sex = sex; } public String getMobile() { return mobile; } public void setMobile(String mobile) { this .mobile = mobile; } public String getEmail() { return email; } public void setEmail(String email) { this .email = email; } public String getNote() { return note; } public void setNote(String note) { this .note = note; } public TPosition getPosition() { return position; } public void setPosition(TPosition position) { this .position = position; } public List<TJobHistory> getJobs() { return jobs; } public void setJobs(List<TJobHistory> jobs) { this .jobs = jobs; } public List<HealthReport> getHealthReports() { return healthReports; } public void setHealthReports(List<HealthReport> healthReports) { this .healthReports = healthReports; } public List<TRole> getRoles() { return roles; } public void setRoles(List<TRole> roles) { this .roles = roles; } } |
3、Mapper接口类
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public interface TUserTestMapper { TUser selectByPrimaryKey(Integer id); List<TUser> selectAll(); } |
4、Mapper xml
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<? 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.mybatis.mapper.TUserTestMapper" > < select id = "selectByPrimaryKey" resultType = "TUser" > select id, user_name, real_name, sex, mobile, email, note from t_user_test where id = #{id,jdbcType=INTEGER} </ select > < select id = "selectAll" resultType = "TUser" > select id, user_name, real_name, sex, mobile, email, note from t_user_test </ select > </ mapper > |
5、配置文件
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<? 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 > < properties resource = "db.properties" /> < settings > <!-- 设置自动驼峰转换 --> < setting name = "mapUnderscoreToCamelCase" value = "true" /> <!-- 开启懒加载 --> <!-- 当启用时,有延迟加载属性的对象在被调用时将会完全加载任意属性。否则,每种属性将会按需要加载。默认:true --> < setting name = "aggressiveLazyLoading" value = "false" /> </ settings > <!-- 别名定义 --> < typeAliases > < package name = "com.enjoylearning.mybatis.entity" /> </ typeAliases > < plugins > < plugin interceptor = "com.enjoylearning.mybatis.Interceptors.ThresholdInterceptor" > < property name = "threshold" value = "10" /> </ plugin > < plugin interceptor = "com.github.pagehelper.PageInterceptor" > < property name = "pageSizeZero" value = "true" /> </ plugin > </ plugins > <!--配置environment环境 --> < environments default = "development" > <!-- 环境配置1,每个SqlSessionFactory对应一个环境 --> < environment id = "development" > < transactionManager type = "JDBC" /> < dataSource type = "POOLED" > < property name = "driver" value = "com.mysql.jdbc.Driver" /> < property name = "url" value = "jdbc:mysql://ip:port/test?useUnicode=true" /> < property name = "username" value = "root" /> < property name = "password" value = "123456" /> </ dataSource > </ environment > </ environments > <!-- 映射文件,mapper的配置文件 --> < mappers > <!--直接映射到相应的mapper文件 --> < mapper resource = "sqlmapper/TUserTestMapper.xml" /> </ mappers > </ configuration > |
6、启动测试类
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public class MybatisDemo2 { private SqlSessionFactory sqlSessionFactory; @Before public void init() throws IOException { //--------------------第一阶段--------------------------- // 1.读取mybatis配置文件创SqlSessionFactory String resource = "mybatis-config.xml" ; InputStream inputStream = Resources.getResourceAsStream(resource); // 1.读取mybatis配置文件创SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); inputStream.close(); } @Test //知识点:resultType public void testAutoMapping() throws IOException { // 2.获取sqlSession SqlSession sqlSession = sqlSessionFactory.openSession(); // 3.获取对应mapper TUserTestMapper mapper = sqlSession.getMapper(TUserTestMapper. class ); // 4.执行查询语句并返回多条数据 List<TUser> users = mapper.selectAll(); for (TUser tUser : users) { System.out.println(tUser); } } } |
7、执行结果
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sql语句:“com.mysql.jdbc.JDBC4PreparedStatement@654f0d9c: select id, user_name, real_name, sex, mobile, email, note from t_user_test”执行时间为:35毫秒,已经超过阈值! TUser [id=1, userName=zhangsan, realName=张三, sex=1, mobile=186995587411, email=zhangsan@qq.com, note=zhangsan的备注, positionId=] TUser [id=2, userName=lisi, realName=李四, sex=1, mobile=18677885200, email=lisi@qq.com, note=lisi的备注, positionId=] TUser [id=3, userName=wangwu, realName=王五, sex=2, mobile=18695988747, email=xxoo@163.com, note=wangwu's note, positionId=] |
resultType当返基本类型的时候建议选择,当返回POJO类的时候由于需要完全和数据库字段进行对应,存在不灵活、问题排查难等问题。
二、resultMap
1、resultMap 介绍
resultMap 元素是 MyBatis 中最重要最强大的元素。它可以让你从 90% 的 JDBC ResultSets 数据提取代码中解放出来,在对复杂语句进行联合映射的时候,它很可能可以代替数千行的同等功能的代码。ResultMap 的设计思想是,简单的语句不需要明确的结果映射,而复杂一点的语句只需要描述它们的关系就行了。
2、resultMap属性
属性 | 描述 |
id | 当前命名空间中的一个唯一标识,用于标识一个result map. |
type | 类的完全限定名, 或者一个类型别名. |
autoMapping | 如果设置这个属性,MyBatis将会为这个ResultMap开启或者关闭自动映射。这个属性会覆盖全局的属性 autoMappingBehavior。默认值为:unset。 |
3、使用场景
- 字段有自定义的转化规则
- 复杂的多表查询
4、resultMap子元素属性
- id –一个 ID 结果;标记出作为 ID 的结果可以帮助提高整体性能,一对多的查询中用于结果集合并;
- result – 注入到字段或 JavaBean 属性的普通结果
- association – 一个复杂类型的关联;许多结果将包装成这种类型。关联可以指定为一个 resultMap 元素,或者引用一个
- collection – 一个复杂类型的集合
5、代码演示
实体类,配置文件同上
1、mapper接口
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public interface TUserMapper { List<TUser> selectTestResultMap(); } |
2、Mapper.xml
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<? 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.mybatis.mapper.TUserMapper" > < resultMap id = "UserResultMap" type = "TUser" autoMapping = "true" > < id column = "id" property = "id" /> < result column = "userName" property = "userName" /> < result column = "realName" property = "realName" /> < result column = "sex" property = "sex" /> < result column = "mobile" property = "mobile" /> < result column = "email" property = "email" /> < result column = "note" property = "note" /> < association property = "position" javaType = "TPosition" columnPrefix = "post_" > < id column = "id" property = "id" /> < result column = "name" property = "postName" /> < result column = "note" property = "note" /> </ association > </ resultMap > < select id = "selectTestResultMap" resultMap = "UserResultMap" > select a.id, userName, realName, sex, mobile, email, a.note, b.id post_id, b.post_name, b.note post_note from t_user a, t_position b where a.position_id = b.id </ select > </ mapper > |
3、启动测试
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public class MybatisDemo2 { private SqlSessionFactory sqlSessionFactory; @Before public void init() throws IOException { //--------------------第一阶段--------------------------- // 1.读取mybatis配置文件创SqlSessionFactory String resource = "mybatis-config.xml" ; InputStream inputStream = Resources.getResourceAsStream(resource); // 1.读取mybatis配置文件创SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); inputStream.close(); } @Test public void testResultMap() throws IOException { //--------------------第二阶段--------------------------- // 2.获取sqlSession SqlSession sqlSession = sqlSessionFactory.openSession(); // 3.获取对应mapper TUserMapper mapper = sqlSession.getMapper(TUserMapper. class ); //--------------------第三阶段--------------------------- // 4.执行查询语句并返回单条数据 List<TUser> users = mapper.selectTestResultMap(); for (TUser tUser : users) { System.out.println(tUser.getUserName()); System.out.println(tUser.getPosition().getPostName()); } } } |
4、执行结果
sql语句:“com.mysql.jdbc.JDBC4PreparedStatement@19bb07ed: select
a.id,
userName,
realName,
sex,
mobile,
email,
a.note,
b.id post_id,
b.post_name,
b.note post_note
from t_user a,
t_position b
where a.position_id = b.id”执行时间为:52毫秒,已经超过阈值!
zhangsan
总经理
lisi
零时工
wangwu
总经理
三、结论
当返回对象为基础类型时建议走resultType,当返回对象为POJO时,强制走resultMap。同时可以参考阿里巴巴JAVA开发手册中的5.4.3节,返回要解耦,不讷讷更直接使用resultClass。
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原文链接:https://juejin.cn/post/7082352714297901064