// 为每一个文章文档新增一个image_count字段，用于记录此文章包含的图片个数
db[‘test.articles‘].find({‘title‘:‘wfc test‘}).forEach( function(thisArticle){
    // 这里要强制转为整形，否则会变成浮点数
    // 要用NumberInt转换为整形，用parseInt得到依然是浮点数
    imageCount = NumberInt( thisArticle[‘article_images‘].length )
    db[‘test.articles‘].update({‘_id‘:thisArticle[‘_id‘]}, {$set:{‘image_count‘:imageCount}} )
   })

// 比较精简干练的写法
db.test.articles.find({‘title‘:‘wfc test‘}).forEach( function(thisArticle){
    thisArticle.image_count = NumberInt( thisArticle.article_images.length )
    db.test.articles.save(thisArticle)
  })

// 将文档的字段放入嵌套数组后，再删除该字段(数据结构修改)    
db[‘test.game‘].find({‘article_image‘:{$exists:0}}).forEach( function(thisArticle){
    articleImage = {‘remote‘:thisArticle.game_icon, ‘local‘:thisArticle.game_local_icon,
                    ‘original‘:thisArticle.game_remote_icon, ‘upload‘:thisArticle.icon_upload}
    thisArticle.image_upload = thisArticle.icon_upload
    thisArticle.modify_time = thisArticle.spider_time
    thisArticle.article_image = []
    thisArticle.article_image.push(articleImage)
    delete thisArticle.game_icon
    delete thisArticle.game_local_icon
    delete thisArticle.game_remote_icon
    delete thisArticle.icon_upload
    db[‘test.game‘].save(thisArticle)
})

// 按名称分组统计
db[‘test.articles‘].group({
    key:{‘name‘:1},
    condition:{‘name‘:{$exists:1}},
    $reduce:function(curr, result) {
        result.total += 1
    },
    initial:{total:0},
})