Mybatis 动态SQL - 使用foreach标签查询数据、批量新增、批量修改、删除数据

前面我们介绍了使用Mybatis完成数据的增删改查，并且也了解了如何在Mybatis中使用JDK的日志系统打印日志；本篇我们介绍使用Mybatis的动态SQL完成查询数据、批量新增、批量修改、删除数据。

如果您对数据的增删改查操作和Mybatis集成JDK日志系统不太了解，建议您先进行了解后再阅读本篇，可以参考：

Mybatis查询数据https://blog.csdn.net/m1729339749/article/details/132469672Mybatis 日志(JDK Log)https://blog.csdn.net/m1729339749/article/details/132565362Mybatis 插入、修改、删除https://blog.csdn.net/m1729339749/article/details/132601345

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

-- 如果数据库不存在则创建数据库
CREATE DATABASE IF NOT EXISTS demo DEFAULT CHARSET utf8;
-- 切换数据库
USE demo;
-- 创建用户表
CREATE TABLE IF NOT EXISTS T_USER(
  ID INT PRIMARY KEY,
  USERNAME VARCHAR(32) NOT NULL,
  AGE INT NOT NULL 
);
-- 插入用户数据
INSERT INTO T_USER(ID, USERNAME, AGE)
VALUES(1, '张三', 20),(2, '李四', 22),(3, '王五', 24);

创建了一个名称为demo的数据库；并在库里创建了名称为T_USER的用户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UserInfo类

UserInfo类：

package cn.horse.demo;

public class UserInfo {

    private Integer id;
    private String name;
    private Integer age;

    public UserInfo() { }
    public UserInfo(Integer id, String name, Integer age) {
        this.id = id;
        this.name = name;
        this.age = age;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public Integer getId() {
        return id;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public Integer getAge() {
        return age;
    }

    @Override
    public String toString() {
        StringBuilder stringBuilder = new StringBuilder();
        stringBuilder.append('{');
        stringBuilder.append("id: " + this.id);
        stringBuilder.append(", ");
        stringBuilder.append("name: " + this.name);
        stringBuilder.append(", ");
        stringBuilder.append("age: " + this.age);
        stringBuilder.append('}');
        return stringBuilder.toString();
    }
}

2、Mapper配置文件

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

    
        SELECT
            ID,
            USERNAME name,
            AGE
        FROM T_USER
    

3、引入配置文件

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

4、会话工具类

在cn.horse.demo包下新建SqlSessionUtils工具类

package cn.horse.demo;

import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.InputStream;
import java.util.Objects;

public class SqlSessionUtils {

    private static final SqlSessionFactory sqlSessionFactory;
    static {
        // 读取mybatis配置文件
        InputStream inputStream = ClassLoader.getSystemClassLoader().getResourceAsStream("mybatis-config.xml");
        // 根据配置创建SqlSession工厂
        sqlSessionFactory = new SqlSessionFactoryBuilder()
                .build(inputStream);
    }

    /**
     * 开启会话
     * @return
     */
    public static SqlSession openSession() {
        return sqlSessionFactory.openSession();
    }

    /**
     * 关闭会话
     * @param sqlSession
     */
    public static void closeSession(SqlSession sqlSession) {
        if(Objects.nonNull(sqlSession)) {
            sqlSession.close();
        }
    }
}

5、JDK 日志系统配置

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

handlers=java.util.logging.ConsoleHandler
.level=INFO

cn.horse.demo.UserInfoMapper.level=FINER
java.util.logging.ConsoleHandler.level=ALL
java.util.logging.ConsoleHandler.formatter=java.util.logging.SimpleFormatter
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下创建JdkLogConfig类

JdkLogConfig类：

package cn.horse.demo;

import java.io.IOException;
import java.io.InputStream;
import java.util.logging.LogManager;

public class JdkLogConfig {

    public JdkLogConfig() {
        try {
            InputStream inputStream = ClassLoader.getSystemClassLoader().getResourceAsStream("logging.properties");
            LogManager.getLogManager().readConfiguration(inputStream);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

6、启动程序

package cn.horse.demo;

import org.apache.ibatis.session.SqlSession;

import java.util.ArrayList;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        // 引入JDK日志配置
        System.setProperty("java.util.logging.config.class", "cn.horse.demo.JdkLogConfig");
        find("cn.horse.demo.UserInfoMapper.findAll", null);
    }

    private static void find(String statement, Object parameter) {
        SqlSession sqlSession = null;
        try {
            sqlSession = SqlSessionUtils.openSession();
            List userInfoList = sqlSession.selectList(statement, parameter);
            for (UserInfo userInfo: userInfoList) {
                System.out.println(userInfo);
            }
        } finally {
            SqlSessionUtils.closeSession(sqlSession);
        }
    }
}

执行后的结果如下：

三、foreach标签

foreach标签用于对数组或可迭代对象的遍历

foreach标签的格式如下：

collection：数组或可迭代对象

item：数组中的元素或本次迭代的元素

index：数组中的索引或本地迭代的序号

open：指定开头的字符串

close：指定结尾的字符串

separator：迭代之间的分隔符

注意：如果可迭代对象是Map对象（或者Map.Entry对象的集合）时，index是键，item是值

四、使用foreach批量插入

在UserInfoMapper.xml配置文件中新增insert标签，并写入insert语句：

    INSERT INTO T_USER(ID,
        USERNAME,
        AGE)
    VALUES
    
        (#{userInfo.id}, #{userInfo.name}, #{userInfo.age})
    

在启动程序中新建batchInsert方法

private static void batchInsert(List userInfoList) {
    SqlSession sqlSession = null;
    try {
        sqlSession = SqlSessionUtils.openSession();
        sqlSession.insert("cn.horse.demo.UserInfoMapper.insert", userInfoList);
        sqlSession.commit();
    } finally {
        SqlSessionUtils.closeSession(sqlSession);
    }
}

调用batchInsert方法插入数据，并查询

List userInfoList = new ArrayList<>();
userInfoList.add(new UserInfo(11, "张三1", 20));
userInfoList.add(new UserInfo(12, "李四1", 22));
userInfoList.add(new UserInfo(13, "王五1", 24));
batchInsert(userInfoList);
find("cn.horse.demo.UserInfoMapper.findAll", null);

执行后的结果如下：

五、使用foreach查询数据

foreach标签常用于构建IN条件语句；

在UserInfoMapper.xml配置文件中新增select标签：

    SELECT
        ID,
        USERNAME name,
        AGE
    FROM T_USER
    
        ID IN
        
            #{id}
        
    

查询数据

find("cn.horse.demo.UserInfoMapper.findByIdList", Arrays.asList(11, 12, 13));

执行后的结果如下：

六、使用foreach批量修改

在UserInfoMapper.xml配置文件中新增update标签，并写入update语句：

    
        UPDATE T_USER
        
            
                USERNAME = #{userInfo.name},
            
            
                AGE = #{userInfo.age},
            
        
        WHERE ID = #{userInfo.id}
    

在启动程序中新建batchUpdate方法：

private static void batchUpdate(List userInfoList) {
    SqlSession sqlSession = null;
    try {
        sqlSession = SqlSessionUtils.openSession();
        sqlSession.update("cn.horse.demo.UserInfoMapper.update", userInfoList);
        sqlSession.commit();
    } finally {
        SqlSessionUtils.closeSession(sqlSession);
    }
}

调用batchUpdate方法更新数据，并查询

List userInfoList = new ArrayList<>();
userInfoList.add(new UserInfo(11, "张三2", null));
userInfoList.add(new UserInfo(12, "李四2", 30));
userInfoList.add(new UserInfo(13, "王五2", null));
batchUpdate(userInfoList);
find("cn.horse.demo.UserInfoMapper.findByIdList", Arrays.asList(11, 12, 13));

执行后的结果如下：

2023-09-03 10:28:11.873 详细 cn.horse.demo.UserInfoMapper.update - ==>  Preparing: UPDATE T_USER SET USERNAME = ? WHERE ID = ? ; UPDATE T_USER SET USERNAME = ?, AGE = ? WHERE ID = ? ; UPDATE T_USER SET USERNAME = ? WHERE ID = ? ; 
2023-09-03 10:28:11.909 详细 cn.horse.demo.UserInfoMapper.update - ==> Parameters: 张三2(String), 11(Integer), 李四2(String), 30(Integer), 12(Integer), 王五2(String), 13(Integer)
Exception in thread "main" org.apache.ibatis.exceptions.PersistenceException: 
### Error updating database.  Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'UPDATE T_USER
             SET USERNAME = '李四2',
                
          ' at line 5
### The error may involve defaultParameterMap
### The error occurred while setting parameters
### SQL: UPDATE T_USER              SET USERNAME = ?              WHERE ID = ?          ;              UPDATE T_USER              SET USERNAME = ?,                                                       AGE = ?              WHERE ID = ?          ;              UPDATE T_USER              SET USERNAME = ?              WHERE ID = ?          ;
### Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'UPDATE T_USER
             SET USERNAME = '李四2',
                
          ' at line 5
	at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.update(DefaultSqlSession.java:200)
	at cn.horse.demo.Main.batchUpdate(Main.java:48)
	at cn.horse.demo.Main.main(Main.java:29)
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'UPDATE T_USER
             SET USERNAME = '李四2',
                
          ' at line 5
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:77)
	at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:499)
	at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:480)
	at com.mysql.jdbc.Util.handleNewInstance(Util.java:403)
	at com.mysql.jdbc.Util.getInstance(Util.java:386)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:944)
	at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3933)
	at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3869)
	at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2524)
	at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2675)
	at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2465)
	at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1915)
	at com.mysql.jdbc.PreparedStatement.execute(PreparedStatement.java:1254)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:568)
	at org.apache.ibatis.logging.jdbc.PreparedStatementLogger.invoke(PreparedStatementLogger.java:59)
	at jdk.proxy3/jdk.proxy3.$Proxy3.execute(Unknown Source)
	at org.apache.ibatis.executor.statement.PreparedStatementHandler.update(PreparedStatementHandler.java:46)
	at org.apache.ibatis.executor.statement.RoutingStatementHandler.update(RoutingStatementHandler.java:74)
	at org.apache.ibatis.executor.SimpleExecutor.doUpdate(SimpleExecutor.java:50)
	at org.apache.ibatis.executor.BaseExecutor.update(BaseExecutor.java:117)
	at org.apache.ibatis.executor.CachingExecutor.update(CachingExecutor.java:76)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.update(DefaultSqlSession.java:198)
	... 2 more

从上面执行的情况来看，SQL执行过程中报错了，原因是我们批量更新使用的是同时执行多条更新语句，而JDBC是不支持的；解决方式是在JDBC连接中添加连接属性allowMultiQueries=true

修改mybatis-config.xml配置文件：

在配置文件中我们仅修改了jdbc:mysql://localhost:3306/demo?useUnicode=true&useSSL=false&characterEncoding=utf8&allowMultiQueries=true

再次执行后的结果如下：

七、使用foreach批量删除

在UserInfoMapper.xml配置文件中新增delete标签，并写入delete语句：

    DELETE FROM T_USER
    
        ID IN
        
            #{id}
        
    

在启动程序中新建batchDelete方法：

private static void batchDelete(List idList) {
    SqlSession sqlSession = null;
    try {
        sqlSession = SqlSessionUtils.openSession();
        sqlSession.delete("cn.horse.demo.UserInfoMapper.delete", idList);
        sqlSession.commit();
    } finally {
        SqlSessionUtils.closeSession(sqlSession);
    }
}

调用batchDelete方法更新数据，并查询

batchDelete(Arrays.asList(11, 12, 13));
find("cn.horse.demo.UserInfoMapper.findByIdList", Arrays.asList(11, 12, 13));

执行后的结果如下：