Mongo db 2.2 aggregation like a champ
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This document provides an overview of aggregation in MongoDB. It introduces aggregation concepts and code examples. Key points covered include: - The $group operator allows grouping documents and calculating aggregates like average on a field. - The aggregation pipeline allows applying a series of operators like $match, $limit, $project, and $unwind to documents. - Common operators like $group, $project, and $unwind are explained briefly with examples of their input and output.
![{ "_id" : "silver", "score" : 17, "house" : "A" }
db.scores.aggregate({$group:
{_id:"$house", avg:{$avg:"$score"}}});
{
"result":[
{"_id" : "B","avg" : 20.333333333333332},
{"_id" : "A","avg" : 19.333333333333332}
],
"ok":1
}](https://image.slidesharecdn.com/mongodb2-2aggregation-121127232939-phpapp02/85/Mongo-db-2-2-aggregation-like-a-champ-4-320.jpg)
Mongo db 2.2 aggregation like a champ
- 2. Map/Reduce pain Aggregation framework - Concepts - Code demo ...Whatever comes our way
- 3. Documents Emit (0..* ) Reduce • One chance at transform • Good for large IO • In/Out of Javascript costly • Imparts "non-interactiveness" Finalize • All I wanted was a group-by!
- 4. { "_id" : "silver", "score" : 17, "house" : "A" } db.scores.aggregate({$group: {_id:"$house", avg:{$avg:"$score"}}}); { "result":[ {"_id" : "B","avg" : 20.333333333333332}, {"_id" : "A","avg" : 19.333333333333332} ], "ok":1 }
- 5. Pipeline Operators ("stage") Collectors, Transformers (operator type) Expressions ("transform“,”evaluate”)
- 6. All docs* One at a time* "The" => "A" Documents operator operator operator * not really, not always, it depends, kinda.
- 7. $group $match $limit $skip $project $unwind $sort $group is why we are here.. but need not be last stage
- 8. $group In: doc, Out: aggregated by _id specified $project In: doc, Out: new doc, shaped to your liking $unwind In: array, Out: same doc + 1 array element
- 10. Download - mongodb.org v 2.2 Ask – 10gen, Google groups, IRC (people use them) Consult / Train - nuri@plusnconsulting.com