db.collection.count()¶

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Definition
Behavior
Examples

Definition¶

db.collection.count(<query>)¶

Returns the count of documents that would match a find() query. The db.collection.count() method does not perform the find() operation but instead counts and returns the number of results that match a query.

The db.collection.count() method has the following parameter:

Parameter	Type	Description
`query`	document	The query selection criteria.

Behavior¶

On a sharded cluster, db.collection.count() can result in an inaccurate count if orphaned documents exist or if a chunk migration is in progress.

To avoid these situations, on a sharded cluster, use the $group stage of the db.collection.aggregate() method to $sum the documents. For example, the following operation counts the documents in a collection:

copy

db.collection.aggregate(
   [
      { $group: { _id: null, count: { $sum: 1 } } }
   ]
)

To get a count of documents that match a query condition, include the $match stage as well:

copy

db.collection.aggregate(
   [
      { $match: <query condition> },
      { $group: { _id: null, count: { $sum: 1 } } }
   ]
)

See Perform a Count for an example.

Examples¶

Count all Documents in a Collection¶

To count the number of all documents in the orders collection, use the following operation:

copy

db.orders.count()

This operation is equivalent to the following:

copy

db.orders.find().count()

Count all Documents that Match a Query¶

Count the number of the documents in the orders collection with the field ord_dt greater than new Date('01/01/2012'):

copy

db.orders.count( { ord_dt: { $gt: new Date('01/01/2012') } } )

The query is equivalent to the following:

copy

db.orders.find( { ord_dt: { $gt: new Date('01/01/2012') } } ).count()

← db.collection.aggregate() db.collection.copyTo() →