MongoDB

MongoDB is an open source cross-platform document-oriented database program. Classified as a NoSQL database program, MongoDB uses JSON-like documents with optional schemas

 Aggregation Pipeline 

An aggregation pipeline consists of one or more stages that process documents:

• Each stage performs an operation on the input documents. For example, a stage can filter documents, group documents, and calculate values.
• The  output from a stage are passed to the next stage.
• An aggregation pipeline can return results for groups of documents. For example, return the total, average, maximum, and minimum values

Complete Aggregation Pipeline Examples

db.orders.insertMany( [

   { _id: 0, name: "Pepperoni", size: "small", price: 19,

     quantity: 10, date: ISODate( "2021-03-13T08:14:30Z" ) },

   { _id: 1, name: "Pepperoni", size: "medium", price: 20,

     quantity: 20, date : ISODate( "2021-03-13T09:13:24Z" ) },

   { _id: 2, name: "Pepperoni", size: "large", price: 21,

     quantity: 30, date : ISODate( "2021-03-17T09:22:12Z" ) },

   { _id: 3, name: "Cheese", size: "small", price: 12,

     quantity: 15, date : ISODate( "2021-03-13T11:21:39.736Z" ) },

   { _id: 4, name: "Cheese", size: "medium", price: 13,

     quantity:50, date : ISODate( "2022-01-12T21:23:13.331Z" ) },

   { _id: 5, name: "Cheese", size: "large", price: 14,

     quantity: 10, date : ISODate( "2022-01-12T05:08:13Z" ) },

   { _id: 6, name: "Vegan", size: "small", price: 17,

     quantity: 10, date : ISODate( "2021-01-13T05:08:13Z" ) },

   { _id: 7, name: "Vegan", size: "medium", price: 18,

     quantity: 10, date : ISODate( "2021-01-13T05:10:13Z" ) }

] )

Calculate Total Order Quantity

  db.orders.aggregate( [

   // Stage 1: Filter pizza order documents by pizza size

   {

      $match: { size: "medium" }

   },

   // Stage 2: Group remaining documents by pizza name and calculate total quantity

   {

      $group: { _id: "$name", totalQuantity: { $sum: "$quantity" } }

   }

] )