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求大佬指点，关于多表联合计算的问题 我项目用的springboot+vue，现在的业务需求是:有a b c d(id，min，max，cal_num)四张表: a根据外键id选择获取b中符合的数据，和a中的某列计算(加减乘除)，得到sum1；同理，再获取c中的数据计算sum2；之后a再根据前面的数据sum1和sum2，加减乘除得到sum，当sum满足在d中的某一行的min，max范围后，获取cal_num和sum计算，得到我们要的最终值。此操作涉及到批量操作，批量操作a中的某些行，请问该如何实现:前端，后端，还是数据库函数实现......对了，前面得到的sum1 sum2 和最终值还要存到另一张表中。真的求大佬! 在哪一端实现，还有怎么操作，我现在有点懵逼。我好像没陈述清除，我说仔细一点：a(aid,av,bid,cid)b(bid,bv)c(cid,cv)d(did,dmin,dmax,dv)整个的计算方法是：result=(av+avbv+avcv)*dv。括号里的选择哪个bv、vc，是根据a里面的bid，cid。而选取哪个dv值，是根据括号里的值判断的，dmin<(av+avbv+avcv)<dmax。而av，avbv，avcv，result都会存到另一个表。此操作涉及到批量操作，批量操作a中的某些行。不知道应该在后端，前端，还是数据库（函数）实现，求大佬指点。EmperorWS
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mybatis报Communications link failure 我有定时任务执行数据库查询，每几分钟一次，压根不会超时，看日志最后一个包也是19ms之前发送的，为什么会报数据库链接失败呢？我的代码里有自己写了一个mybatis的拦截器，使用了pagehelper的5版本，同时使用了threadlocal来进行数据传递（拦截器里用了这个threadlocal），同时写了一个webListener来进行请求之后的销毁处理，这些会影响到我们的连接池关闭吗？感觉应该不会啊[09:10:03:163] [10.221.231.214] [INFO] [schedu...read-1] [HttpReportJobDaoImpl] - task completed request is : TaskCompletedRequest{context=null, taskId=5010566995, status=FAILED, msg='org.springframework.dao.DataAccessResourceFailureException: ### Error querying database. Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed.Connection was implicitly closed due to underlying exception/error: ** BEGIN NESTED EXCEPTION ** com.mysql.jdbc.exceptions.jdbc4.CommunicationsException MESSAGE: Communications link failure Last packet sent to the server was 19 ms ago. STACKTRACE: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure Last packet sent to the server was 19 ms ago. at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.lang.reflect.Constructor.newInstance(Constructor.java:422) at com.mysql.jdbc.Util.handleNewInstance(Util.java:406) at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1074) at com.mysql.jdbc.MysqlIO.send(MysqlIO.java:3134) at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1818) at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1961) at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2543) at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1737) at com.mysql.jdbc.PreparedStatement.execute(PreparedStatement.java:998) at sun.reflect.GeneratedMethodAccessor138.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:497) at org.apache.tomcat.jdbc.pool.StatementFacade$StatementProxy.invoke(StatementFacade.java:114) at com.sun.proxy.$Proxy189.execute(Unknown Source) at org.apache.ibatis.executor.statement.PreparedStatementHandler.query(PreparedStatementHandler.java:63) at org.apache.ibatis.executor.statement.RoutingStatementHandler.query(RoutingStatementHandler.java:79) at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:63) at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:324) at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156) at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:109) at com.github.pagehelper.PageInterceptor.intercept(PageInterceptor.java:108) at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:61) at com.sun.proxy.$Proxy184.query(Unknown Source) at sun.reflect.GeneratedMethodAccessor134.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:497) at org.apache.ibatis.plugin.Invocation.proceed(Invocation.java:49) at com.jd.jr.jcca.configuration.mybatis.interceptor.MybatisDataPermissionInterceptor.intercept(MybatisDataPermissionInterceptor.java:64) at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:61) at com.sun.proxy.$Proxy184.query(Unknown Source) at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:148) at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:141) at org.apache.ibatis.session.defaults.DefaultSqlSession.selectOne(DefaultSqlSession.java:77) at sun.reflect.GeneratedMethodAccessor141.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:497) at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:433) at com.sun.proxy.$Proxy130.selectOne(Unknown Source) at org.mybatis.spring.SqlSessionTemplate.selectOne(SqlSessionTemplate.java:166) at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:82) at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:59) at com.sun.proxy.$Proxy167.getByApplyId(Unknown Source) at com.jd.jr.jcca.bankmanager.service.impl.ApplyDetailServiceImpl.saveApplyDetail(ApplyDetailServiceImpl.java:39) at com.jd.jr.jcca.mq.fmq.listener.FirstSubmitSuccessListener.processApplyMessage(FirstSubmitSuccessListener.java:57) at com.jd.jr.jcca.mq.fmq.listener.FirstSubmitSuccessListener.onMessage(FirstSubmitSuccessListener.java:38) at com.jdjr.fmq.client.consumer.TopicConsumer$1.call(TopicConsumer.java:769) at com.jdjr.fmq.client.consumer.TopicConsumer$1.call(TopicConsumer.java:725) at com.jdjr.fmq.client.consumer.ConsumerRetryLoop.execute(ConsumerRetryLoop.java:34) at com.jdjr.fmq.client.consumer.TopicConsumer.dispatchMessages(TopicConsumer.java:725) at com.jdjr.fmq.client.consumer.TopicConsumer$TopicMessageDispatcher.dispatch(TopicConsumer.java:879) at com.jdjr.fmq.client.consumer.GroupConsumer.pull(GroupConsumer.java:343) at com.jdjr.fmq.client.consumer.GroupConsumer$QueueConsumer.run(GroupConsumer.java:571) at java.lang.Thread.run(Thread.java:745) Caused by: java.net.SocketException: Connection timed out at java.net.SocketOutputStream.socketWrite0(Native Method) at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:109) at java.net.SocketOutputStream.write(SocketOutputStream.java:153) at java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:82) at java.io.BufferedOutputStream.flush(BufferedOutputStream.java:140) at com.mysql.jdbc.MysqlIO.send(MysqlIO.java:3119) ... 49 more ** END NESTED EXCEPTION ** ### The error may exist in com/jd/jr/jcca/unicard/dao/mapper/TUnCallbackLogMapper.java (best guess) ### The error may involve com.jd.jr.jcca.unicard.dao.mapper.TUnCallbackLogMapper.queryBatchForJob ### The error occurred while executing a query ### SQL: SELECT * FROM t_un_callback_log t WHERE t.delete_flag = 1 AND t.status IN ('INIT', 'FAIL') AND t.try_num < 5 AND t.next_time between ? and now() ORDER BY id DESC LIMIT ? ### Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed.Connection was implicitly closed due to underlying exception/error: ** BEGIN NESTED EXCEPTION ** com.mysql.jdbc.exceptions.jdbc4.CommunicationsException MESSAGE: Communications link failure Last packet sent to the server was 19 ms ago. STACKTRACE: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure Last packet sent to the server was 19 ms ago.梦见存在
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vscode运行vue项目后，修改代码终端报错 问题描述npm run serve启动项目后，修改代码，项目会自动重新编译，但是eslint会报错。修改的内容：将import {Vue} from "vue-property-decorator"的vue重新复制粘贴了一次。问题出现的平台版本及自己尝试过哪些方法系统：win10工具: vscode项目用的 vue ui图形界面自动创建的尝试过的方法：ctrl+c强制结束然后等一会儿在npm run serve才好相关代码错误提示：ERROR Failed to compile with 1 errors 14:03:51 error in ./src/components/login/Login.vue Module Error (from ./node_modules/eslint-loader/index.js): F:\learn\vue\vue-typescript\src\components\login\Login.vue 2:3 warning Delete `··` prettier/prettier 3:5 warning Delete `␍⏎········` prettier/prettier 5:1 warning Delete `····` prettier/prettier 6:1 warning Delete `····` prettier/prettier 7:1 warning Delete `····` prettier/prettier 8:1 warning Replace `········<el-form·:label-position="labelPosition"·label-width="80px"·:model="loginUser">` with `····<el-form␍⏎······:label-position="labelPosition"␍⏎······label-width="80px"␍⏎······:model="loginUser"` prettier/prettier 9:5 warning Insert `>` prettier/prettier 10:1 warning Delete `······` prettier/prettier 11:5 warning Replace `␍⏎················<el-input·v-model="loginUser.username"></el-input>␍⏎····` with `····<el-input·v-model="loginUser.username"></el-input>` prettier/prettier 14:7 warning Delete `······` prettier/prettier 15:1 warning Delete `····` prettier/prettier 16:7 warning Delete `······` prettier/prettier 17:3 warning Delete `··␍⏎··········` prettier/prettier 19:1 warning Replace `····␍⏎············` with `······` prettier/prettier 21:5 warning Delete `␍⏎········` prettier/prettier 23:3 warning Delete `··␍⏎····` prettier/prettier 28:45 warning Insert `;` prettier/prettier 32:1 warning Delete `··` prettier/prettier 32:5 error Type string trivially inferred from a string literal, remove type annotation @typescript-eslint/no-inferrable-types 33:3 warning Delete `··` prettier/prettier 34:3 warning Replace `··public·username:·string·=·''` with `public·username:·string·=·""` prettier/prettier 34:5 error Type string trivially inferred from a string literal, remove type annotation @typescript-eslint/no-inferrable-types 35:1 warning Replace `····public·password:·string·=·''` with `··public·password:·string·=·""` prettier/prettier 35:5 error Type string trivially inferred from a string literal, remove type annotation @typescript-eslint/no-inferrable-types ✖ 24 problems (3 errors, 21 warnings) 3 errors and 21 warnings potentially fixable with the `--fix` option. @ ./src/router/index.ts 5:0-49 14:13-18 @ ./src/main.ts @ multi (webpack)-dev-server/client?http://192.168.124.4:8080/sockjs-node (webpack)/hot/dev-server.js ./src/main.ts Type checking in progress... No type errors found Version: typescript 3.7.5 Time: 1111ms我的代码：<template> <div class="login"> <h3>Hello, this is login page</h3> <h5>account:admin<br />password: admin</h5> <el-form :label-position="labelPosition" label-width="80px" :model="loginUser"> <el-form-item label="用户名"> <el-input v-model="loginUser.username"></el-input> </el-form-item> <el-form-item label="密码"> <el-input v-model="loginUser.password"></el-input> </el-form-item> </el-form> </div> </template> <script lang="ts"> import {Vue} from "vue-property-decorator" import LoginEntity from "../../entity/LoginEntity"; export default class Login extends Vue { public labelPosition: string = "left"; public loginUser: LoginEntity = new LoginEntity(); public username: string = ''; public password: string = ''; } </script> 你期待的结果是什么？实际看到的错误信息又是什么？期待结果：正常编译实际错误：见错误提示代码。二手代码程序员
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react-hooks为什么使用useRef可以保存上次的值？ 我在useEffect中把state状态赋值给ref对象的current属性，也就是说这个preCountUseRef.current拿到最新的state值，可是在DOM中显示上次的state值相关代码import React, { useState, useRef, useEffect } from 'react' const App = () => { const [count, setCount] = useState(0) const preCountUseRef = useRef(count) useEffect(() => { preCountUseRef.current = count }) return ( <div> <p>precount: {preCountUseRef.current}</p> <p>You clicked {count} times</p> <button onClick={() => setCount(() => count + 1)}>Click me</button> </div> ) } export default App能否详细说明一下useRef运行机制以及对官网解释的"useRef就像是可以在其.current属性中保存一个可变值的“盒子”。"这句话该怎么理解呢？唐吉
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c++函数对象疑问 在家等待开工，看了本c++入门书，在看一篇文章中有介绍函数对象，自己搜了下，但是不清楚这种写法是什么意思：template <class T> struct less : binary_function<T, T, bool> { bool operator()(const T& x, const T& y) const { return x < y; } };这种写法中的binary_function<T, T, bool>是啥意思？常见的函数对象写法：class increment { private: int num; public: increment(int n) : num(n) { } int operator () (int arr_num) const { return num + arr_num; } };我理解的函数对象用法是：increment(10); //等价于 increment.operator()(10);另外一个例子中也存在疑问： #include <complex> // std::complex #include <iostream> // std::cout/endl #include <unordered_map> // std::unordered_map #include <unordered_set> // std::unordered_set using namespace std; namespace std { template <typename T> struct hash<complex<T>> { size_t operator()(const complex<T>& v) const noexcept { hash<T> h; cout << "Hello,world"<<endl; return h(v.real()) + h(v.imag()); } }; } // namespace std int main() { unordered_set<int> s{ 1, 1, 2, 3, 5, 8, 13, 21 }; unordered_map<complex<double>, double> umc{{{1.0, 1.0}, 1.4142}, {{3.0, 4.0}, 5.0}}; return 0; } 这里我在hash中添加了打印，结果打印了三次hello,world.但是Unorder_map中只有两个元素，讲道理两个元素插入，计算hash也是计算两次呀，为什么打印三次呢?风清扬
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