Question

Basic problem

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

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 );
});

Unfortunatly they both error:

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

The link also has this one:

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

and that one errors:

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

So how can I get those records?

Timespan

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.

This is the schema:

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

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

EDIT

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 );
    }
  );
}

Answer 1

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.

Try this instead to find the newest:

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

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

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) { ... });

Or even pass a string to sort:

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