MongoDB – Transformations¶

db.users.aggregate([
   {
     $project:
      {
         name: 1,
         first: { $arrayElemAt: [ "$favorites", 0 ] },  // 0: premier élément
         last: { $arrayElemAt: [ "$favorites", -1 ] }  // -1: dernier élément
      }
   }
])

{ "_id" : 1, "name" : "dave123", favorites: [ "chocolate", "cake", "butter", "apples" ] }
{ "_id" : 2, "name" : "li", favorites: [ "apples", "pudding", "pie" ] }
{ "_id" : 3, "name" : "ahn", favorites: [ "pears", "pecans", "chocolate", "cherries" ] }
{ "_id" : 4, "name" : "ty", favorites: [ "ice cream" ] }

db.sales.aggregate(
  [
    // Première étape
    {
      $group :
        { _id : "$item",
          totalSaleAmount: { $sum: { $multiply: [ "$price", "$quantity" ] } }}
     },
     // Deuxième étape
     {
       $match: { "totalSaleAmount": { $gte: 100 } }
     }
   ]
 )

db.sales.aggregate([
  {
    $group : {
       _id : null,
       totalSaleAmount: { $sum: { $multiply: [ "$price", "$quantity" ] } },
       averageQuantity: { $avg: "$quantity" },
       count: { $sum: 1 }
    }
  }
])

db.restaurants.aggregate([
    {
        $group:
        {
          _id: {borough: "$borough", cuisine: "$cuisine"},
          nbRestos: { $sum : 1}
        }
    },
    {
        $sort: {_id:1}
   }
])

db.books.aggregate([
   { $group : { _id : "$author", books: { $push: "$title" } } }
 ])

{ "_id" : 8751, "title" : "The Banquet", "author" : "Dante", "copies" : 2 },
{ "_id" : 8752, "title" : "Divine Comedy", "author" : "Dante", "copies" : 1 },
{ "_id" : 8645, "title" : "Eclogues", "author" : "Dante", "copies" : 2 },
{ "_id" : 7000, "title" : "The Odyssey", "author" : "Homer", "copies" : 10 },
{ "_id" : 7020, "title" : "Iliad", "author" : "Homer", "copies" : 10 }

{ "_id" : "Homer", "books" : [ "The Odyssey", "Iliad" ] }
{ "_id" : "Dante", "books" : [ "The Banquet", "Divine Comedy", "Eclogues" ] }

.aggregate([ { $unwind: "$books" }, { $project: { author: "$_id", title: "$books"} } ])