未定義のNode.js＆Jadeのプロパティ 'length'を読み取ることができません

Question

私は上記のエラーが表示されます。変数が一致しないので、私はこのエラーを、おそらくその前に見ました。

マイルート.jsファイル：

var express = require('express'); 
var router = express.Router(); 
var mongo = require('mongodb'); 
var db = require('monk')('localhost/nodeblog'); 

router.get('/add', function(req, res, next) { 
    var categories = db.get('categories'); 

    categories.find({}, {}, function(err, categories){ 
    res.render('addpost', { 
     'title': 'Add Post', 
     'categories': categories 
    }); 
    }); 
}) 

router.post('/add', function(req, res, next){ 
    //Get form values 
    var title = req.body.title; 
    var category = req.body.category; 
    var body = req.body.body; 
    var author = req.body.author; 
    var date = new Date(); 

    if (req.hasOwnProperty('file')) { 
    console.log('Uploading File...'); 

    //File info 
    var mainImageOriginalName = req.files.mainimage.originalname; 
    var mainImageName = req.files.mainimage.name; 
    var mainImageMime = req.files.mainimage.mimetype; 
    var mainImagePath = req.files.mainimage.path; 
    var mainImageExt = req.files.mainimage.extension; 
    var mainImageSize = req.files.mainimage.size; 
    } else { 
    //Set a Default Image 
    var mainImageName = 'noimage.png'; 
    } 

    //Form Validation 
    req.checkBody('title', 'Title field is required').notEmpty(); 
    req.checkBody('body', 'Body field is required'); 

    //Check Errors 
    var errors = req.validationErrors(); 

    if(errors){ 
    res.render('addpost', { 
     'errors': errors, 
     'title': title, 
     'body': body 
    }); 
    } else { 
    var posts = db.get('post'); 

    //Submit to DB 
    posts.insert({ 
     'title': title, 
     'body': body, 
     'category': category, 
     'date': date, 
     'author': author, 
     'mainimage': mainImageName 
    }, function(err, post){ 
     if(err){ 
     res.send('There was an issue submitting the post'); 
     } else { 
     req.flash('succes', 'post submitted'); 
     res.location('/'); 
     res.redirect('/'); 
     } 
    }); 
    } 
}); 

module.exports = router; 

マイ.jadeファイル：

extends layout 

block content 
    h1=title 
    ul.errors 
    if error 
     each error, i in errors 
     li.alert.alert-danger #{error.msg} 
    form(method='post', action='/posts/add', enctype='multipart/form-data') 
    .form-group 
     label Title: 
     input.form-control(name='title', type='text') 
    .form-group 
     label Category 
     select.form-control(name='category') 
     each category, i in categories 
      option(value='#{category.title}') #{category.title} 
    .form-group 
     label Body 
     textarea.form-control(name='body', id='body') 
    .form-group 
     label Main Image: 
     input.form-control(name='mainimage', type='file') 
    .form-group 
     label Author: 
     select.form-control(name='author') 
     option(value='Marko') Marko 
     option(value='John Do') John Do 
    input.btn.btn-default(name='submit', type='submit', value='Save') 
    script(src='/ckeditor/ckeditor.js') 
    script 
     | CKEDITOR.replace('body'); 

と完全なエラーログ：

TypeError: C:\projects\nodeblog\views\addpost.jade:16 
    14|  label Category 
    15|  select.form-control(name='category') 
    > 16|   each category, i in categories 
    17|   option(value='#{category.title}') #{category.title} 
    18|  .form-group 
    19|  label Body 

Cannot read property 'length' of undefined 
    at eval (eval at <anonymous> (C:\projects\nodeblog\node_modules\jade\lib\index.js:218:8), <anonymous>:204:31) 
    at eval (eval at <anonymous> (C:\projects\nodeblog\node_modules\jade\lib\index.js:218:8), <anonymous>:241:4) 
    at eval (eval at <anonymous> (C:\projects\nodeblog\node_modules\jade\lib\index.js:218:8), <anonymous>:374:22) 
    at res (C:\projects\nodeblog\node_modules\jade\lib\index.js:219:38) 
    at Object.exports.renderFile (C:\projects\nodeblog\node_modules\jade\lib\index.js:380:38) 
    at Object.exports.renderFile (C:\projects\nodeblog\node_modules\jade\lib\index.js:370:21) 
    at View.exports.__express [as engine] (C:\projects\nodeblog\node_modules\jade\lib\index.js:417:11) 
    at View.render (C:\projects\nodeblog\node_modules\express\lib\view.js:126:8) 
    at tryRender (C:\projects\nodeblog\node_modules\express\lib\application.js:639:10) 
    at EventEmitter.render (C:\projects\nodeblog\node_modules\express\lib\application.js:591:3) 
    at ServerResponse.render (C:\projects\nodeblog\node_modules\express\lib\response.js:961:7) 
    at C:\projects\nodeblog\routes\posts.js:48:9 
    at Layer.handle [as handle_request] (C:\projects\nodeblog\node_modules\express\lib\router\layer.js:95:5) 
    at next (C:\projects\nodeblog\node_modules\express\lib\router\route.js:131:13) 
    at Route.dispatch (C:\projects\nodeblog\node_modules\express\lib\router\route.js:112:3) 
    at Layer.handle [as handle_request] (C:\projects\nodeblog\node_modules\express\lib\router\layer.js:95:5) 

誰かが助け場合、私は感謝です。

Answer 1

エラーオブジェクトをコンソールし、下のコードでカテゴリを取得しているかどうかを確認してください。

router.get('/add', function(req, res, next) { 
     var categories = db.get('categories'); 

     categories.find({}, {}, function(err, categories){ 
** console error and check categories type should be an array** 
     res.render('addpost', { 
      'title': 'Add Post', 
      'categories': categories 
     }); 
     }); 
    })