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Aggregation in MongoDB
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Aggregation in MongoDB

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  • 1. Aggregation
  • 2. Pipeline Unix pipeline Piping command line operations ls -al | grep '^d‘ |
  • 3. Pipeline • Piping aggregation operations $match | $sort | $skip | more Stream of documents Result document
  • 4. Example { title : “mongo DB " , author : "bob" , posted : new Date() , pageViews : 5 , tags : [ "fun" , "good" , "fun" ] , language : “English”, other : { foo : 5 } }
  • 5. 1. Count – return number of documents in collection. > db.user.count(); you can also pass query, and MongoDB will count number of result for that query. 2. Distinct The distinct commands find all the distinct values for given key in collection. db.runCommand ( {“distinct” : “collection name” ,”key” : “key field” } ) 3. Match >db.blog.aggregate({$match : {pageViews : {$gt : 1 ,$lt :50 } } } ) 4. Limit > db.blog.aggregate({$limit : 5 } ) 5. Sort >db.blog.find( ).sort({title : 1} )
  • 6. 6. $project Include, exclude or rename fields Insert computed fields Create sub-document fields selecting and excluding fields >db.blog.aggregate{ { “$project” : { _id : 0 , title : 1 , language : 1} } }
  • 7. { _id: 375, title: “mongo DB", ISBN: "9781857150193", available: true, pages: 218, subjects: [ “Test", “Pune", "1920s" ], language: "English" } { title: “mongo DB, language: "English" }
  • 8. Insert computed field Db.blog.aggregate( { “$project” : { title : 1 , newPageViews : { $add : *“$pageViews” ,10]} } }
  • 9. Rename Page Views db.blog.aggregate( { title : 1, newPageViews : “$pageViews” } ) Create and Populate new Field that hold subfields db.blog.aggregate( {"$project" : { title : 1 , stats:{pv : "$pageViews" , foo : "$other.foo" } } })
  • 10. Groups Each document in collection has following form { "_id": “413710", "city": “Pune", "state": “MH", "pop": 5574, "loc": [ -74.016323, 40.710537 ] }
  • 11. Group db.blog.aggregate( { $group : { _id : "$state", totalPop : { $sum : "$pop" } } }, { $match : {totalPop : { $gte : 10*1000 } } } )
  • 12. Usage and Limit • collection.aggregate() method – Mongo shell – Most drivers • aggregate database command
  • 13. Limitations Result limited by BSON document size Final command result Intermediate shard results Pipeline operator memory limits Some BSON types unsupported Binary, Code, deprecated types
  • 14. Map Reduce • Map reduce operation handle complex aggregation task.