• Mybatis 动态SQL – 使用trim标签替代where,set标签

    前面几篇我们介绍了where,set标签的使用；本篇我们继续介绍如何使用Mybatis提供的tirm标签替代where,set标签。

    如果您对where,set标签不太了解，建议您先进行了解后再阅读本篇，可以参考：

    Mybatis 动态SQL – 使用if,where标签动态生成条件语句

    Mybatis 动态SQL – 使用if,set标签动态生成更新语句

    一、数据准备

    这里我们直接使用脚本初始化数据库中的数据

    1. -- 如果数据库不存在则创建数据库
    2. CREATE DATABASE IF NOT EXISTS demo DEFAULT CHARSET utf8;
    3. -- 切换数据库
    4. USE demo;
    5. -- 创建用户表
    6. CREATE TABLE IF NOT EXISTS T_TEACHER(
    7.   ID INT PRIMARY KEY COMMENT '教师编号',
    8.   TEACHER_NAME VARCHAR(64) NOT NULL COMMENT '教师名称',
    9.   DEPARTMENT VARCHAR(16) NOT NULL COMMENT '所属部门',
    10.   BIRTH DATE NOT NULL COMMENT '出生年月',
    11.   DEGREE VARCHAR(16) NOT NULL COMMENT '学历(ZK:专科, BK:本科, YJS:研究生, BS:博士)'
    12. );
    13. -- 插入用户数据
    14. INSERT INTO T_TEACHER(ID, TEACHER_NAME, DEPARTMENT, BIRTH, DEGREE)
    15. VALUES(1, '张三1', '001', '1990-06-12', 'BK'),
    16.       (2, '李四1', '002', '1992-05-10', 'BK'),
    17.       (3, '张三2', '003', '1988-01-15', 'YJS'),
    18.       (4, '李四2', '001', '1979-03-10', 'BK'),
    19.       (5, '李四3', '003', '1995-08-16', 'YJS');

    创建了一个名称为demo的数据库；并在库里创建了名称为T_TEACHER的教师表并向表中插入了数据

    二、环境搭建

    1、创建实体类

    在cn.horse.demo下创建TeacherInfo实体类：

    TeacherInfo类：

    1. package cn.horse.demo;
    2.  
    3. import java.time.LocalDate;
    4.  
    5. public class TeacherInfo {
    6.     private Integer id;
    7.     private String name;
    8.     private String department;
    9.     private LocalDate birth;
    10.     private String degree;
    11.  
    12.     public void setId(Integer id) {
    13.         this.id = id;
    14.     }
    15.  
    16.     public void setDepartment(String department) {
    17.         this.department = department;
    18.     }
    19.  
    20.     public void setDegree(String degree) {
    21.         this.degree = degree;
    22.     }
    23.  
    24.     @Override
    25.     public String toString() {
    26.         StringBuilder stringBuilder = new StringBuilder();
    27.         stringBuilder.append("{ ");
    28.         stringBuilder.append("id: ");
    29.         stringBuilder.append(this.id);
    30.         stringBuilder.append(", ");
    31.         stringBuilder.append("name: ");
    32.         stringBuilder.append(this.name);
    33.         stringBuilder.append(", ");
    34.         stringBuilder.append("department: ");
    35.         stringBuilder.append(this.department);
    36.         stringBuilder.append(", ");
    37.         stringBuilder.append("birth: ");
    38.         stringBuilder.append(this.birth);
    39.         stringBuilder.append(", ");
    40.         stringBuilder.append("degree: ");
    41.         stringBuilder.append(this.degree);
    42.         stringBuilder.append(" }");
    43.         return stringBuilder.toString();
    44.     }
    45. }

    2、Mapper配置文件

    在resources的目录下新建TeacherInfoMapper.xml配置文件

    1. "1.0" encoding="UTF-8" ?>
    2. mapper
    3.         PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
    4.         "https://mybatis.org/dtd/mybatis-3-mapper.dtd">
    5. <mapper namespace="cn.horse.demo.TeacherInfoMapper">
    6.  
    7.     <select id="findById" resultType="cn.horse.demo.TeacherInfo">
    8.         SELECT
    9.             ID,
    10.             TEACHER_NAME name,
    11.             DEPARTMENT,
    12.             BIRTH,
    13.             DEGREE
    14.         FROM T_TEACHER
    15.         WHERE ID = #{id}
    16.     select>
    17.  
    18.     <select id="findByQuery" parameterType="cn.horse.demo.TeacherInfoQuery" resultType="cn.horse.demo.TeacherInfo">
    19.         SELECT
    20.             ID,
    21.             TEACHER_NAME name,
    22.             DEPARTMENT,
    23.             BIRTH,
    24.             DEGREE
    25.         FROM T_TEACHER
    26.         <where>
    27.             <if test="null != degree and '' != degree">
    28.                 AND DEGREE = #{degree}
    29.             if>
    30.             <if test="null != department and '' != department">
    31.                 AND DEPARTMENT = #{department}
    32.             if>
    33.         where>
    34.     select>
    35.  
    36.     <update id="updateByEntity" parameterType="cn.horse.demo.TeacherInfo">
    37.         UPDATE T_TEACHER
    38.         <set>
    39.             <if test="null != department and '' != department">
    40.                 DEPARTMENT = #{department},
    41.             if>
    42.             <if test="null != degree and '' != degree">
    43.                 DEGREE = #{degree},
    44.             if>
    45.         set>
    46.         WHERE ID = #{id}
    47.     update>
    48. mapper>

    3、引入配置文件

    在resources下新建mybatis-config.xml配置文件，并引入TeacherInfoMapper.xml配置文件

    1. "1.0" encoding="UTF-8" ?>
    2. configuration
    3.         PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
    4.         "http://mybatis.org/dtd/mybatis-3-config.dtd">
    5. <configuration>
    6.     <settings>
    7.         <setting name="logImpl" value="JDK_LOGGING"/>
    8.     settings>
    9.  
    10.     <environments default="development">
    11.         <environment id="development">
    12.             <transactionManager type="JDBC"/>
    13.             <dataSource type="POOLED">
    14.                 <property name="driver" value="org.gjt.mm.mysql.Driver"/>
    15.                 <property name="url" value="jdbc:mysql://localhost:3306/demo?useUnicode=true&useSSL=false&characterEncoding=utf8"/>
    16.                 <property name="username" value="root"/>
    17.                 <property name="password" value="horse"/>
    18.             dataSource>
    19.         environment>
    20.     environments>
    21.  
    22.     <mappers>
    23.         <mapper resource="demo/TeacherInfoMapper.xml" />
    24.     mappers>
    25. configuration>

    4、会话工具类

    在cn.horse.demo包下新建SqlSessionUtils工具类

    1. package cn.horse.demo;
    2.  
    3. import org.apache.ibatis.session.SqlSession;
    4. import org.apache.ibatis.session.SqlSessionFactory;
    5. import org.apache.ibatis.session.SqlSessionFactoryBuilder;
    6.  
    7. import java.io.InputStream;
    8. import java.util.Objects;
    9.  
    10. public class SqlSessionUtils {
    11.  
    12.     private static final SqlSessionFactory sqlSessionFactory;
    13.     static {
    14.         // 读取mybatis配置文件
    15.         InputStream inputStream = ClassLoader.getSystemClassLoader().getResourceAsStream("mybatis-config.xml");
    16.         // 根据配置创建SqlSession工厂
    17.         sqlSessionFactory = new SqlSessionFactoryBuilder()
    18.                 .build(inputStream);
    19.     }
    20.  
    21.     /**
    22.      * 开启会话
    23.      * @return
    24.      */
    25.     public static SqlSession openSession() {
    26.         return sqlSessionFactory.openSession();
    27.     }
    28.  
    29.     /**
    30.      * 关闭会话
    31.      * @param sqlSession
    32.      */
    33.     public static void closeSession(SqlSession sqlSession) {
    34.         if(Objects.nonNull(sqlSession)) {
    35.             sqlSession.close();
    36.         }
    37.     }
    38. }

    5、JDK 日志系统配置

    在resources的目录下新建logging.properties配置文件

    1. handlers=java.util.logging.ConsoleHandler
    2. .level=INFO
    3.  
    4. cn.horse.demo.TeacherInfoMapper.level=FINER
    5. java.util.logging.ConsoleHandler.level=ALL
    6. java.util.logging.ConsoleHandler.formatter=java.util.logging.SimpleFormatter
    7. java.util.logging.SimpleFormatter.format=%1$tY-%1$tm-%1$td %1$tT.%1$tL %4$s %3$s - %5$s%6$s%n

    在cn.horse.demo下新建JdkLogConfig类：

    JdkLogConfig类：

    1. package cn.horse.demo;
    2.  
    3. import java.io.IOException;
    4. import java.io.InputStream;
    5. import java.util.logging.LogManager;
    6.  
    7. public class JdkLogConfig {
    8.  
    9.     public JdkLogConfig() {
    10.         try {
    11.             InputStream inputStream = ClassLoader.getSystemClassLoader().getResourceAsStream("logging.properties");
    12.             LogManager.getLogManager().readConfiguration(inputStream);
    13.         } catch (IOException e) {
    14.             throw new RuntimeException(e);
    15.         }
    16.     }
    17. }

    6、启动程序

    1. package cn.horse.demo;
    2.  
    3. import org.apache.ibatis.session.SqlSession;
    4.  
    5. import java.util.List;
    6.  
    7. public class Main {
    8.     public static void main(String[] args) {
    9.         // 引入JDK日志配置
    10.         System.setProperty("java.util.logging.config.class", "cn.horse.demo.JdkLogConfig");
    11.  
    12.         // 查询学历为本科的教师
    13.         TeacherInfoQuery query = new TeacherInfoQuery();
    14.         query.setDegree("BK");
    15.         findAll("cn.horse.demo.TeacherInfoMapper.findByQuery", query);
    16.  
    17.         // 更新编号为2的教师
    18.         TeacherInfo teacherInfo = new TeacherInfo();
    19.         teacherInfo.setId(2);
    20.         teacherInfo.setDegree("BK");
    21.         updateByEntity("cn.horse.demo.TeacherInfoMapper.updateByEntity", teacherInfo);
    22.         // 查询编号为2的教师
    23.         findById("cn.horse.demo.TeacherInfoMapper.findById", 2);
    24.     }
    25.  
    26.     private static void findAll(String statement, TeacherInfoQuery query) {
    27.         SqlSession sqlSession = null;
    28.         try {
    29.             sqlSession = SqlSessionUtils.openSession();
    30.             List teacherInfoList = sqlSession.selectList(statement, query);
    31.             for (TeacherInfo teacherInfo: teacherInfoList) {
    32.                 System.out.println(teacherInfo);
    33.             }
    34.         } finally {
    35.             SqlSessionUtils.closeSession(sqlSession);
    36.         }
    37.     }
    38.  
    39.     private static void updateByEntity(String statement, TeacherInfo teacherInfo) {
    40.         SqlSession sqlSession = null;
    41.         try {
    42.             sqlSession = SqlSessionUtils.openSession();
    43.             sqlSession.update(statement, teacherInfo);
    44.             sqlSession.commit();
    45.         } finally {
    46.             SqlSessionUtils.closeSession(sqlSession);
    47.         }
    48.     }
    49.  
    50.     private static void findById(String statement, Integer id) {
    51.         SqlSession sqlSession = null;
    52.         try {
    53.             sqlSession = SqlSessionUtils.openSession();
    54.             TeacherInfo teacherInfo = sqlSession.selectOne(statement, id);
    55.             System.out.println(teacherInfo);
    56.         } finally {
    57.             SqlSessionUtils.closeSession(sqlSession);
    58.         }
    59.     }
    60. }

    执行后的结果如下：

    三、trim标签替代where标签

    之前我们介绍过where标签的两个作用：

    （1）判断是否存在条件，如果条件不存在，则不再拼接where；如果条件存在，则拼接where

    （2）剔除where后面多余的AND或OR

    下面我们给出where等效的trim标签配置：

    1. <trim prefix="where" prefixOverrides="AND | OR">
    2.     
    3. trim>

    prefix属性：当trim标签中内容不为空时，则拼接prefix的属性值

    prefixOverrides属性：当trim标签中的内容以AND或OR开头时，则剔除AND或OR

    下面我们修改TeacherInfoMapper.xml配置文件中的findByQuery查询语句：

    1. <select id="findByQuery" parameterType="cn.horse.demo.TeacherInfoQuery" resultType="cn.horse.demo.TeacherInfo">
    2.     SELECT
    3.         ID,
    4.         TEACHER_NAME name,
    5.         DEPARTMENT,
    6.         BIRTH,
    7.         DEGREE
    8.     FROM T_TEACHER
    9.     <trim prefix="where" prefixOverrides="AND | OR">
    10.         <if test="null != degree and '' != degree">
    11.             AND DEGREE = #{degree}
    12.         if>
    13.         <if test="null != department and '' != department">
    14.             AND DEPARTMENT = #{department}
    15.         if>
    16.     trim>
    17. select>

    测试：

    1. // 引入JDK日志配置
    2. System.setProperty("java.util.logging.config.class", "cn.horse.demo.JdkLogConfig");
    3.  
    4. // 查询学历为研究生的教师
    5. TeacherInfoQuery query = new TeacherInfoQuery();
    6. query.setDegree("YJS");
    7. findAll("cn.horse.demo.TeacherInfoMapper.findByQuery", query);

    执行后的结果如下：

    四、trim标签替代set标签

    之前我们介绍过set标签可用于剔除更新语句中多余的逗号

    下面我们给出set等效的trim标签配置：

    1. <trim prefix="set" suffixOverrides=",">
    2.     
    3. trim>

    prefix属性：当trim标签中内容不为空时，则拼接prefix的属性值

    suffixOverrides属性：当trim标签中的内容以逗号结束时，则剔除逗号

    下面我们修改TeacherInfoMapper.xml配置文件中的updateByEntity查询语句：

    1. <update id="updateByEntity" parameterType="cn.horse.demo.TeacherInfo">
    2.     UPDATE T_TEACHER
    3.     <trim prefix="set" suffixOverrides=",">
    4.         <if test="null != department and '' != department">
    5.             DEPARTMENT = #{department},
    6.         if>
    7.         <if test="null != degree and '' != degree">
    8.             DEGREE = #{degree},
    9.         if>
    10.     trim>
    11.     WHERE ID = #{id}
    12. update>

    测试：

    1. // 引入JDK日志配置
    2. System.setProperty("java.util.logging.config.class", "cn.horse.demo.JdkLogConfig");
    3.  
    4. // 更新编号为2的教师
    5. TeacherInfo teacherInfo = new TeacherInfo();
    6. teacherInfo.setId(2);
    7. teacherInfo.setDegree("BK");
    8. updateByEntity("cn.horse.demo.TeacherInfoMapper.updateByEntity", teacherInfo);
    9. // 查询编号为2的教师
    10. findById("cn.horse.demo.TeacherInfoMapper.findById", 2);

    查询的结果如下：

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  • 原文地址：https://blog.csdn.net/m1729339749/article/details/132830398