我通过Ruby宝石“续集”使用PostgreSQL。
我要四舍五入到小数点后两位。
这是我的代码:
SELECT ROUND(AVG(some_column),2)
FROM table
我得到以下错误:
PG::Error: ERROR: function round(double precision, integer) does
not exist (Sequel::DatabaseError)
当我运行以下代码时，我没有得到错误:
SELECT ROUND(AVG(some_column))
FROM table
有人知道我哪里做错了吗?
我想从第一个中间件传递一些变量到另一个中间件，我试着这样做，但有“req。有些变量是一个给定的‘未定义’”。
//app.js
..
app.get('/someurl/', middleware1, middleware2)
...
////middleware1
...
some conditions
...
res.somevariable = variable1;
next();
...
////middleware2
...
some conditions
...
variable = req.somevariable;
...
在新版本的express上有一些中间件的变化，我也在我的代码中做了一些关于这个问题的其他帖子的更改，但我不能得到任何坚持。
我们之前让它工作，但我不记得是什么变化了。
throw new TypeError('Router.use() requires middleware function but got a
^
TypeError: Router.use() requires middleware function but got a Object
node ./bin/www
js-bson: Failed to load c++ bson extension, using pure JS version
js-bson: Failed to load c++ bson extension, using pure JS version
/Users/datis/Documents/bb-dashboard/node_modules/express/lib/router/index.js:438
throw new TypeError('Router.use() requires middleware function but got a
^
TypeError: Router.use() requires middleware function but got a Object
at /Users/datis/Documents/bb-dashboard/node_modules/express/lib/router/index.js:438:13
at Array.forEach (native)
at Function.use (/Users/datis/Documents/bb-dashboard/node_modules/express/lib/router/index.js:436:13)
at /Users/datis/Documents/bb-dashboard/node_modules/express/lib/application.js:188:21
at Array.forEach (native)
at Function.use (/Users/datis/Documents/bb-dashboard/node_modules/express/lib/application.js:185:7)
at Object.<anonymous> (/Users/datis/Documents/bb-dashboard/app.js:46:5)
at Module._compile (module.js:456:26)
at Object.Module._extensions..js (module.js:474:10)
at Module.load (module.js:356:32)
app.js
var express = require('express');
var path = require('path');
var favicon = require('serve-favicon');
var logger = require('morgan');
var cookieParser = require('cookie-parser');
var bodyParser = require('body-parser');
var mongoose = require('mongoose');
var session = require('express-session');
var MongoClient = require('mongodb').MongoClient;
var routes = require('./routes/index');
var users = require('./routes/users');
var Users = require('./models/user');
var Items = require('./models/item');
var Store = require('./models/store');
var StoreItem = require('./models/storeitem');
var app = express();
//set mongo db connection
var db = mongoose.connection;
MongoClient.connect("mongodb://localhost:27017/test", function(err, db) {
if(!err) {
console.log("We are connected");
}
});
// var MONGOHQ_URL="mongodb://localhost:27017/test"
// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'ejs');
// uncomment after placing your favicon in /public
//app.use(favicon(__dirname + '/public/favicon.ico'));
app.use(logger('dev'));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: false }));
app.use(cookieParser());
app.use(session({
secret: 'something',
resave: true,
saveUninitialized: true
}));
app.use('/', routes);
app.use('/users', users);
app.use(express.static(path.join(__dirname, 'public')));
// catch 404 and forward to error handler
// app.use(function(req, res, next) {
// var err = new Error('Not Found');
// err.status = 404;
// next(err);
// });
// Make our db accessible to our router
app.use(function(req, res, next){
req.db = db;
next();
});
// error handlers
// development error handler
// will print stacktrace
if (app.get('env') === 'development') {
app.use(function(err, req, res, next) {
res.status(err.status || 500);
res.render('error', {
message: err.message,
error: err
});
});
}
// production error handler
// no stacktraces leaked to user
app.use(function(err, req, res, next) {
res.status(err.status || 500);
res.render('error', {
message: err.message,
error: {}
});
});
module.exports = app;
由于版本的原因，这个问题的答案似乎已经改变了。感谢尼克
我试图添加一个属性来表达使用typescript从中间件请求对象。但是，我不知道如何向对象添加额外的属性。如果可能的话，我宁愿不用括号。
我正在寻找一个解决方案，允许我写类似的东西(如果可能的话):
app.use((req, res, next) => {
req.property = setProperty();
next();
});
在我问app.router之前，我想我至少应该解释一下我认为在使用中间件时会发生什么。要使用中间件，需要使用的函数是app.use()。当中间件正在执行时，它将使用next()调用下一个中间件，或者使它不再调用更多的中间件。这意味着我放置中间件调用的顺序很重要，因为一些中间件依赖于其他中间件，而靠近末尾的一些中间件甚至可能不被调用。
Today I was working on my application and had my server running in the background. I wanted to make some changes and refresh my page and see the changes immediately. Specifically, I was making changes to my layout. I couldn't get it to work so I searched Stack Overflow for the answer and found this question. It says to make sure that express.static() is beneath require('stylus'). But when I was looking at that OP's code, I saw that he had his app.router call at the very end of his middleware calls, and I tried to figure out why that was.
当我做我的express. js应用程序(3.0.0rc4版)，我使用命令express app -sessions -css stylus和在我的app.js文件的代码来设置与我的app.router以上的express.static()和要求('stylus')调用。所以看起来，如果它已经这样设置了，那么它应该保持这样。
在重新安排我的代码，这样我就可以看到我的手写笔的变化，它看起来像这样:
app.configure(function(){
//app.set() calls
//app.use() calls
//...
app.use(app.router);
app.use(require('stylus').middleware(__dirname + '/public'));
app.use(express.static(__dirname + '/public', {maxAge: 31557600000}));
});
app.get('/', routes.index);
app.get('/test', function(req, res){
res.send('Test');
});
So I decided that the first step would be to find out why it is important to even have app.router in my code. So I commented it out, started my app and navigated to /. It displayed my index page just fine. Hmm, maybe it worked because I was exporting the routing from my routes file (routes.index). So next I navigated to /test and it displayed Test on the screen. Haha, OK, I have no idea what app.router does. Whether it is included in my code or not, my routing is fine. So I am definitely missing something.
所以我的问题是:
谁能解释一下app.router是做什么的，它的重要性，以及我应该把它放在中间件调用的哪里?如果我能得到一个关于express.static()的简要解释，那就太好了。据我所知，express.static()是我的信息的缓存，如果应用程序找不到所请求的页面，它将检查缓存，看看它是否存在。
我已经开始使用webpack2(准确地说，v2.3.2)，在重新创建我的配置后，我一直遇到一个问题，我似乎无法解决我得到(提前为丑陋的转储道歉):
ERROR in ./src/main.js
Module not found: Error: Can't resolve 'components/DoISuportIt' in '[absolute path to my repo]/src'
resolve 'components/DoISuportIt' in '[absolute path to my repo]/src'
Parsed request is a module
using description file: [absolute path to my repo]/package.json (relative path: ./src)
Field 'browser' doesn't contain a valid alias configuration
aliased with mapping 'components': '[absolute path to my repo]/src/components' to '[absolute path to my repo]/src/components/DoISuportIt'
using description file: [absolute path to my repo]/package.json (relative path: ./src)
Field 'browser' doesn't contain a valid alias configuration
after using description file: [absolute path to my repo]/package.json (relative path: ./src)
using description file: [absolute path to my repo]/package.json (relative path: ./src/components/DoISuportIt)
as directory
[absolute path to my repo]/src/components/DoISuportIt doesn't exist
no extension
Field 'browser' doesn't contain a valid alias configuration
[absolute path to my repo]/src/components/DoISuportIt doesn't exist
.js
Field 'browser' doesn't contain a valid alias configuration
[absolute path to my repo]/src/components/DoISuportIt.js doesn't exist
.jsx
Field 'browser' doesn't contain a valid alias configuration
[absolute path to my repo]/src/components/DoISuportIt.jsx doesn't exist
[[absolute path to my repo]/src/components/DoISuportIt]
[[absolute path to my repo]/src/components/DoISuportIt]
[[absolute path to my repo]/src/components/DoISuportIt.js]
[[absolute path to my repo]/src/components/DoISuportIt.jsx]
package.json
{
"version": "1.0.0",
"main": "./src/main.js",
"scripts": {
"build": "webpack --progress --display-error-details"
},
"devDependencies": {
...
},
"dependencies": {
...
}
}
关于它所抱怨的浏览器字段，我能够找到的文档是:package-browser-field-spec。也有webpack文档，但它似乎默认开启:aliasFields: ["browser"]。我尝试在我的包中添加一个浏览器字段。Json，但这似乎没有任何好处。
webpack.config.js
import path from 'path';
const source = path.resolve(__dirname, 'src');
export default {
context: __dirname,
entry: './src/main.js',
output: {
path: path.resolve(__dirname, 'dist'),
filename: '[name].js',
},
resolve: {
alias: {
components: path.resolve(__dirname, 'src/components'),
},
extensions: ['.js', '.jsx'],
},
module: {
rules: [
{
test: /\.(js|jsx)$/,
include: source,
use: {
loader: 'babel-loader',
query: {
cacheDirectory: true,
},
},
},
{
test: /\.css$/,
include: source,
use: [
{ loader: 'style-loader' },
{
loader: 'css-loader',
query: {
importLoader: 1,
localIdentName: '[path]___[name]__[local]___[hash:base64:5]',
modules: true,
},
},
],
},
],
},
};
src / main.js
import DoISuportIt from 'components/DoISuportIt';
src /组件/ DoISuportIt / index.jsx
export default function() { ... }
为完整起见，.babelrc
{
"presets": [
"latest",
"react"
],
"plugins": [
"react-css-modules"
],
"env": {
"production": {
"compact": true,
"comments": false,
"minified": true
}
},
"sourceMaps": true
}
我做错了什么/遗漏了什么?
我有一个叫做people的mongodb集合 其架构如下:
people: {
name: String,
friends: [{firstName: String, lastName: String}]
}
现在，我有一个非常基本的快速应用程序连接到数据库，并成功地创建“人”与一个空的朋友数组。
在应用程序的次要位置，有一个添加好友的表单。表单接收firstName和lastName，然后是带有名称字段的POSTs，同样用于引用适当的people对象。
我有一个困难的时间做的是创建一个新的朋友对象，然后“推”到朋友数组。
我知道当我通过mongo控制台这样做时，我使用$push作为查找标准后的第二个参数的更新函数，但我似乎找不到合适的方法让猫鼬这样做。
db.people.update({name: "John"}, {$push: {friends: {firstName: "Harry", lastName: "Potter"}}});
假设mongodb文档(表)“用户”是
{
_id: 1,
name: {
first: 'John',
last: 'Backus'
},
birth: new Date('Dec 03, 1924'),
death: new Date('Mar 17, 2007'),
contribs: ['Fortran', 'ALGOL', 'Backus-Naur Form', 'FP'],
awards: [
{
award: 'National Medal',
year: 1975,
by: 'NSF'
},
{
award: 'Turing Award',
year: 1977,
by: 'ACM'
}
]
}
// ...and other object(person)s
我想找到那个必须在1975年被授予“国家勋章”的人 可能还有其他人在不同的年份获得过这个奖项。
我如何使用奖项类型和年份找到这个人。这样我就能得到准确的人。
我有一个基本的Node.js应用程序，我试图使用Express框架启动。我有一个views文件夹，其中有一个index.html文件。但是我在加载网页时收到以下错误:
Error: Cannot find module 'html'
下面是我的代码。
var express = require('express');
var app = express.createServer();
app.use(express.staticProvider(__dirname + '/public'));
app.get('/', function(req, res) {
res.render('index.html');
});
app.listen(8080, '127.0.0.1')
我错过了什么?
我有一个Express Node.js应用程序，但我也有一个机器学习算法在Python中使用。是否有一种方法可以从我的Node.js应用程序调用Python函数来利用机器学习库的强大功能?