[MySql]MySql中外键设置 以及Java/MyBatis程序对存在外键关联无法删除的规避

在MySql设定两张表，其中product表的主键设定成orderTb表的外键，具体如下：

产品表：

create table product(id INT(11) PRIMARY KEY,name VARCHAR(32) );

订单表：

create table orderTb(id INT(11) PRIMARY KEY,productid INT(11), FOREIGN KEY(productid) REFERENCES product(id) )；

给产品表插入数据如下：

给订单表插入数据如下：

在MySql-Front工具中写SQL文“DELETE from product where id=1”，由于主外键关联，工具会如下报错：

如果用java程序去删（工程下载：https://files.cnblogs.com/files/xiandedanteng/product191006_2.rar ）

删除代码：

package com.hy;

import java.io.Reader;

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 org.apache.log4j.Logger;

public class DeleteProductTest {
    private static Logger logger = Logger.getLogger(DeleteProductTest.class);

    public static void main(String[] args) throws Exception{
        long startTime = System.currentTimeMillis();
        Reader reader=Resources.getResourceAsReader("mybatis-config.xml");

        SqlSessionFactory ssf=new SqlSessionFactoryBuilder().build(reader);
        reader.close();

        SqlSession session=ssf.openSession();
        logger.info("Commit Status="+session.getConnection().getAutoCommit());

        try {
            ProductMapper pm=session.getMapper(ProductMapper.class);
            int changed=pm.deleteById(1);
            session.commit();
            logger.info("Committed! Chenged Record Num="+changed);

            long endTime = System.currentTimeMillis();
            logger.info("Time elapsed:" + toDhmsStyle((endTime - startTime)/1000) + ".");
        }catch(Exception ex) {
            logger.error("Error/Exception happened when executing the meothod'ProductMapper.deleteById(1)' because '"+ex.getMessage()+"'.");
            session.rollback();
            logger.info("Rollbacked.");
        }
        finally {
            session.close();
        }
    }

    // format seconds to day hour minute seconds style
    // Example 5000s will be formatted to 1h23m20s
    public static String toDhmsStyle(long allSeconds) {
        String DateTimes = null;

        long days = allSeconds / (60 * 60 * 24);
        long hours = (allSeconds % (60 * 60 * 24)) / (60 * 60);
        long minutes = (allSeconds % (60 * 60)) / 60;
        long seconds = allSeconds % 60;

        if (days > 0) {
            DateTimes = days + "d" + hours + "h" + minutes + "m" + seconds + "s";
        } else if (hours > 0) {
            DateTimes = hours + "h" + minutes + "m" + seconds + "s";
        } else if (minutes > 0) {
            DateTimes = minutes + "m" + seconds + "s";
        } else {
            DateTimes = seconds + "s";
        }

        return DateTimes;
    }
}

Mapper接口类

package com.hy;

public interface ProductMapper {
    int deleteById(long id);
}

Mapper.xml

<?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.hy.ProductMapper">
    <delete id="deleteById">
        delete from product where id=#{id}
    </delete>
</mapper>

用程序强行去删，会出现异常：

com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException

执行下来，控制台输出会是：

 INFO [main] - Commit Status=false
ERROR [main] - Error/Exception happened when executing the meothod'ProductMapper.deleteById(1)' because '
### Error updating database.  Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cannot delete or update a parent row: a foreign key constraint fails (`test`.`orderTb`, CONSTRAINT `orderTb_ibfk_1` FOREIGN KEY (`productid`) REFERENCES `product` (`id`))
### The error may involve defaultParameterMap
### The error occurred while setting parameters
### SQL: delete from product where id=?
### Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cannot delete or update a parent row: a foreign key constraint fails (`test`.`orderTb`, CONSTRAINT `orderTb_ibfk_1` FOREIGN KEY (`productid`) REFERENCES `product` (`id`))'.
 INFO [main] - Rollbacked.

因此，在删除时，应该有选择地辨认并跳过这种异常才行。具体程序如下：

package com.hy;

import java.io.Reader;

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 org.apache.log4j.Logger;

public class DeleteProductTest2 {
    private static Logger logger = Logger.getLogger(DeleteProductTest2.class);

    public static void main(String[] args) throws Exception{
        long startTime = System.currentTimeMillis();
        Reader reader=Resources.getResourceAsReader("mybatis-config.xml");

        SqlSessionFactory ssf=new SqlSessionFactoryBuilder().build(reader);
        reader.close();

        SqlSession session=ssf.openSession();
        logger.info("Commit Status="+session.getConnection().getAutoCommit());
        int totalChanged=0;

        try {
            ProductMapper pm=session.getMapper(ProductMapper.class);

            long[] arr= {1,2,3,4,5};
            for(long id:arr) {
                logger.info("deleteById id="+id+" started!");
                try {
                    int changed=pm.deleteById(id);
                    session.commit();
                    totalChanged+=changed;
                    logger.info("Committed! Chenged Record Num="+changed);
                }catch(Exception ex) {
                    if(ex.getMessage().contains("foreign key constraint fails")){ // 用 ex instanceof 识别不出来，故而用这种方式
                        logger.error("ForeignKey collide Conflict happened when executing the meothod'ProductMapper.deleteById("+id+")'.");
                        continue;
                    }else {
                        logger.error("Other Error/Exception happened when executing the meothod'ProductMapper.deleteById("+id+")' because '"+ex.getMessage()+"'.");
                        session.rollback();
                        logger.info("Rollbacked.");
                    }
                }

                logger.info("deleteById id="+id+" finished!");
            }
        }catch(Exception ex) {
            logger.error("Error/Exception happened when executing the meothod'ProductMapper.deleteById(1)' because '"+ex.getMessage()+"'.");
            session.rollback();
            logger.info("Rollbacked.");
        }
        finally {
            session.close();
        }

        logger.info("Changed recoed count="+totalChanged);
        long endTime = System.currentTimeMillis();
        logger.info("Time elapsed:" + toDhmsStyle((endTime - startTime)/1000) + ".");
    }

    // format seconds to day hour minute seconds style
    // Example 5000s will be formatted to 1h23m20s
    public static String toDhmsStyle(long allSeconds) {
        String DateTimes = null;

        long days = allSeconds / (60 * 60 * 24);
        long hours = (allSeconds % (60 * 60 * 24)) / (60 * 60);
        long minutes = (allSeconds % (60 * 60)) / 60;
        long seconds = allSeconds % 60;

        if (days > 0) {
            DateTimes = days + "d" + hours + "h" + minutes + "m" + seconds + "s";
        } else if (hours > 0) {
            DateTimes = hours + "h" + minutes + "m" + seconds + "s";
        } else if (minutes > 0) {
            DateTimes = minutes + "m" + seconds + "s";
        } else {
            DateTimes = seconds + "s";
        }

        return DateTimes;
    }
}

执行后输出如下：

 INFO [main] - Commit Status=false
 INFO [main] - deleteById id=1 started!
ERROR [main] - ForeignKey collide Conflict happened when executing the meothod'ProductMapper.deleteById(1)'.
 INFO [main] - deleteById id=2 started!
ERROR [main] - ForeignKey collide Conflict happened when executing the meothod'ProductMapper.deleteById(2)'.
 INFO [main] - deleteById id=3 started!
ERROR [main] - ForeignKey collide Conflict happened when executing the meothod'ProductMapper.deleteById(3)'.
 INFO [main] - deleteById id=4 started!
 INFO [main] - Committed! Chenged Record Num=1
 INFO [main] - deleteById id=4 finished!
 INFO [main] - deleteById id=5 started!
 INFO [main] - Committed! Chenged Record Num=1
 INFO [main] - deleteById id=5 finished!
 INFO [main] - Changed recoed count=2
 INFO [main] - Time elapsed:10s.

--END-- 2019年10月6日14:52:46