Skip to main content

count

Definition​

The count stage passes a document to the next stage that contains a count of the number of documents input to the stage.

Read the official MongoDB documentation

Syntax​

count has the following form:

count string

Behaviour​

count returns a single document with a single property named with the argument to count and a value of the number of input documents to this stage.

Example​

A collection named scores has the following documents:

{ "_id" : 1, "subject" : "History", "score" : 88 }
{ "_id" : 2, "subject" : "History", "score" : 92 }
{ "_id" : 3, "subject" : "History", "score" : 97 }
{ "_id" : 4, "subject" : "History", "score" : 71 }
{ "_id" : 5, "subject" : "History", "score" : 79 }
{ "_id" : 6, "subject" : "History", "score" : 83 }

The following aggregation excludes documents that have a score less than or equal to 80 and returns the count of the number of passing scores.

aggregate ${object:"scores"}
    match score > 80
    count "passing_scores"
end