Part II of the post MongoDB Aggregation Framework

MongoDB vs SQL

As I know that most of you come from SQL world, I am going to show the equivalence between the sql functions and the functions we will use with the aggregation framework.

Summary

Stages

• $project: Reshapes each document in the stream, include, exclude or rename fields, inject computed fields, create sub-document fields, using mathematical expressions, dates, strings and/or logical (comparison, boolean, control) expressions
• $match: Filters the document stream to allow only matching documents to pass unmodified into the next pipeline stage.
• $redact: Reshapes each document in the stream by restricting the content for each document based on information stored in the documents themselves. Incorporates the functionality of $project and $match.
• $limit: Limits the number of documents passed to the next stage.
• $skip: Skips over the specified number of documents that pass into the stage and passes the remaining documents to the next stage.
• $unwind: Expand documents. Deconstructs an array field from the input documents to output a document for each element.
• $group: Summarize documents. Groups input documents by a specified identifier expression and applies the accumulator expression(s).
• $sort: Order documents by one or more fields.
• $geoNear: Returns an ordered stream of documents based on the proximity to a geospatial point.
• $out: Writes the resulting documents of the aggregation pipeline to a collection. It must be the last stage in the pipeline.

Expressions

For a deeper dive into any of these expressions you can visit this url: http://docs.mongodb.org/manual/meta/aggregation-quick-reference/#expressions

Arithmetic

• $add
• $subtract
• $multiply
• $divide
• $mod

Date

• $dayOfYear
• $dayOfMonth
• $dayOfWeek
• $year
• $month
• $week
• $hour
• $minute
• $second
• $millisecond
• $dateToString

String

• $concat
• $substr
• $toLower
• $toUpper
• $strcasecmp

Logical (Comparison)

• $cmp
• $eq
• $ne
• $gt
• $gte
• $lt
• $lte

Logical (Boolean)

• $and
• $or
• $not

Logical (Control)

• $cond
• $ifNull

Set

• $setEquals
• $setIntersection
• $setUnion
• $setDifference
• $setIsSubset
• $anyElementTrue
• $allElementsTrue

Text Search

• $meta

Array

• $size

Variable

• $map
• $let

Literal

• $literal

Accumulators (available only for the $group stage)

• $sum
• $avg
• $first
• $last
• $max
• $min
• $push
• $addToSet

Single Purpose Aggregation Operations

• Count: MongoDB can return a count of the number of documents that match a query.
• Distinct: The distinct operation takes a number of documents that match a query and returns all of the unique values for a field in the matching documents.
• Group: The group operation takes a number of documents that match a query, and then collects groups of documents based on the value of a field or fields. It returns an array of documents with computed results for each group of documents.

Este obra está bajo una licencia de Creative Commons Reconocimiento-NoComercial-CompartirIgual 4.0 Internacional.