mongodb-aggr-project-datetostring

/*
  Mongodb aggregrate function to do the following task:
  1. date formatting ($project)
  2. match condition
  3. sort
  4. limit
  
  article schema
  
  {
    _id: ObjectId,
    link: String,
    title: String,
    content: String
    pubdate: Date
  }
*/

db.articles.aggregate(
    [
        {
            $match : { "category": "news" }
        },
        {
            $project: {
                yearMonthDay: { $dateToString: { format: "%Y-%m-%d %H:%M:%S", date: "$pubdate" } }
                content: "$content",
                link : "$link",
                title: "$title"
            }
        },
        {
            '$sort': { '_id': -1 }
	}, 
	{
            '$limit': 20
	}
    ]
)