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db.collection.count[query, options]
Important
mongosh Method
This page documents a mongosh
method. This is not the documentation for a language-specific driver, such as Node.js.
For MongoDB API drivers, refer to the language-specific MongoDB driver documentation.
Note
MongoDB drivers compatible with the 4.0 features deprecate their respective cursor and collection count[]
APIs in favor of new APIs for countDocuments[]
and estimatedDocumentCount[]
. For the specific API names for a given driver, see the driver documentation.
Returns the count of documents that
would match a find[]
query for the collection or view. The db.collection.count[]
method does not perform the
find[]
operation but instead counts and returns the number of results that match a query.
| document | The query selection criteria. |
| document | Optional. Extra options for modifying the count. |
The options
document contains the following fields:
| integer | Optional. The maximum number of documents to count. | ||||||||||
| integer | Optional. The number of documents to skip before counting. | ||||||||||
| string or document | Optional. An index name hint or specification for the query. | ||||||||||
| integer | Optional. The maximum amount of time to allow the query to run. | ||||||||||
| string | Optional. Specifies the read concern. The default level is To ensure that a single thread can read its own writes, use
To use a read
concern level of | ||||||||||
| document | Optional. Specifies the collation to use for the operation. Collation allows users to specify language-specific rules for string comparison, such as rules for lettercase and accent marks. The collation option has the following syntax:
When
specifying collation, the If the collation is unspecified but the collection has a default collation [see
If no collation is specified for the collection or for the operations, MongoDB uses the simple binary comparison used in prior versions for string comparisons. You cannot specify multiple collations for an operation. For example, you cannot specify different collations per field, or if performing a find with a sort, you cannot use one collation for the find and another for the sort. |
count[]
is equivalent to the db.collection.find[query].count[]
construct.
Tip
When you call
count[]
without a query predicate, you may receive inaccurate document counts. Without a query predicate, count[]
methods return results based on the collection's metadata, which may
result in an approximate count. In particular,
On a sharded cluster, the resulting count will not correctly filter out orphaned documents.
After an unclean shutdown or file copy based initial sync, the count may be incorrect.
For counts based on collection metadata, see also collStats pipeline stage with the count option.
You cannot use count
and shell helpers
count[]
and db.collection.count[]
in transactions.
For details, see Transactions and Count Operations.
On a sharded cluster, db.collection.count[]
without a query predicate 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
db.collection.aggregate[]
method:
You can use the $count
stage to count the documents. For example, the following operation counts the documents in a collection:
db.collection.aggregate[ [ { $count: "myCount" } ]]
The
$count
stage is equivalent to the following $group
+ $project
sequence:
db.collection.aggregate[ [ { $group: { _id: null, count: { $sum: 1 } } } { $project: { _id: 0 } } ] ]
Tip
See also:
$collStats
to return an approximate count based on the collection's metadata.
Consider a collection with the following index:
When performing a count, MongoDB can return the count using only the index if:
the query can use an index,
the query only contains conditions on the keys of the index, and
the query predicates access a single contiguous range of index keys.
For example, the following operations can return the count using only the index:
db.collection.find[ { a: 5, b: 5 } ].count[] db.collection.find[ { a: { $gt: 5 } } ].count[] db.collection.find[ { a: 5, b: { $gt: 10 } } ].count[]
If, however, the query can use an index but the query predicates do not access a single contiguous range of index keys or the query also contains conditions on fields outside the index, then in addition to using the index, MongoDB must also read the documents to return the count.
db.collection.find[ { a: 5, b: { $in: [ 1, 2, 3 ] } } ].count[] db.collection.find[ { a: { $gt: 5 }, b: 5 } ].count[] db.collection.find[ { a: 5, b: 5, c: 5 } ].count[]
In such cases, during the initial read of the documents, MongoDB pages the documents into memory such that subsequent calls of the same count operation will have better performance.
After an unclean shutdown of a mongod
using the
Wired Tiger storage engine, count statistics reported by count[]
may be inaccurate.
The amount of drift depends on the number of insert, update, or delete operations performed between the last
checkpoint and the unclean shutdown. Checkpoints usually occur every 60 seconds. However, mongod
instances running with non-default
--syncdelay
settings may have more or less frequent checkpoints.
Run validate
on each collection on the mongod
to restore statistics after an unclean shutdown.
After an unclean shutdown:
validate
updates the count statistic in thecollStats
output with the latest value.Other statistics like the number of documents inserted or removed in the
collStats
output are estimates.
Note
This loss of accuracy only applies to
count[]
operations that do not include a query predicate.
Starting in MongoDB 4.2, if the client that issued db.collection.count[]
disconnects before the
operation completes, MongoDB marks db.collection.count[]
for termination using killOp
To count the number of all documents in the orders
collection, use the following operation:
This operation is equivalent to the following:
Count the number of the documents in the orders
collection with the field ord_dt
greater than new
Date['01/01/2012']
:
db.orders.count[ { ord_dt: { $gt: new Date['01/01/2012'] } } ]
The query is equivalent to the following:
db.orders.find[ { ord_dt: { $gt: new Date['01/01/2012'] } } ].count[]