如何在 mongoose.js 中获取最新和最旧的记录(或者只是它们之间的时间跨度) [英] How to get the latest and oldest record in mongoose.js (or just the timespan between them)

问题描述

我有一堆记录，我需要获取最新的(最近的)和最旧的(最近的).

I have a bunch of records and I need to get latest (most recent) and the oldest (least recent).

谷歌搜索时我发现 这个话题 在那里我看到了几个查询:

When googling I found this topic where I saw a couple of queries:

// option 1
Tweet.findOne({}, [], { $orderby : { 'created_at' : -1 } }, function(err, post) {
  console.log( post );
});
// option 2
Tweet.find({}, [], {sort:[['arrival',-1]]}, function(err, post) {
  console.log( post );
});

不幸的是他们都错了:

TypeError: Invalid select() argument. Must be a string or object.

链接也有这个:

Tweet.find().sort('_id','descending').limit(15).find(function(err, post) {
  console.log( post );
});

还有一个错误:

TypeError: Invalid sort() argument. Must be a string or object.

那么我如何获得这些记录?

So how can I get those records?

更理想的是，我只想要最旧和最新记录之间的时间差(秒?)，但我不知道如何开始进行这样的查询.

Even more ideally I just want the difference in time (seconds?) between the oldest and the newest record, but I have no clue on how to start making a query like that.

这是架构:

var Tweet = new Schema({
    body: String
  , fid: { type: String, index: { unique: true } }
  , username: { type: String, index: true }
  , userid: Number
  , created_at: Date
  , source: String
});

我很确定我有最新版本的 mongoDB 和 mongoose.

I'm pretty sure I have the most recent version of mongoDB and mongoose.

这是我根据 JohnnyHK 提供的答案计算时间跨度的方式:

This is how I calc the timespan based on the answer provided by JohnnyHK:

var calcDays = function( cb ) {
  var getOldest = function( cb ) {
    Tweet.findOne({}, {}, { sort: { 'created_at' : 1 } }, function(err, post) {
      cb( null, post.created_at.getTime() );
    });
  }
    , getNewest = function( cb ) {
    Tweet.findOne({}, {}, { sort: { 'created_at' : -1 } }, function(err, post) {
      cb( null, post.created_at.getTime() );
    });
  }

  async.parallel({ 
    oldest: getOldest
  , newest: getNewest
  }
    , function( err, results ) {
      var days = ( results.newest - results.oldest ) / 1000 / 60 / 60 / 24;
      // days = Math.round( days );
      cb( null, days );
    }
  );
}

推荐答案

Mongoose 3.x 抱怨 findOne 调用，因为选择要包含的字段的参数不再支持数组格式.

Mongoose 3.x is complaining about the [] parameter in your findOne calls as the array format is no longer supported for the parameter that selects the fields to include.

试试这个来找到最新的:

Try this instead to find the newest:

Tweet.findOne({}, {}, { sort: { 'created_at' : -1 } }, function(err, post) {
  console.log( post );
});

将 -1 更改为 1 以查找最旧的.

Change the -1 to a 1 to find the oldest.

但是因为您没有使用任何字段选择，所以将几个调用链接在一起会更简洁一些:

But because you're not using any field selection, it's somewhat cleaner to chain a couple calls together:

Tweet.findOne().sort({created_at: -1}).exec(function(err, post) { ... });

或者甚至将字符串传递给 sort:

Or even pass a string to sort:

Tweet.findOne().sort('-created_at').exec(function(err, post) { ... });

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