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db.collection.count(query, options)
This is a mongosh method. This is not the documentation for Node.js or other programming language specific driver methods.
In most cases, mongosh methods work the same way as the legacy mongo shell methods. However, some legacy methods are unavailable in mongosh.
For the legacy mongo shell documentation, refer to the documentation for the corresponding MongoDB Server release:
For MongoDB API drivers, refer to the language specific MongoDB driver documentation.
MongoDB drivers compatible with the 4.0 features deprecate their respective cursor and collection 与4.0功能兼容的MongoDB驱动程序不推荐使用各自的游标和集合count() APIs in favor of new APIs for countDocuments() and estimatedDocumentCount(). count()API，而支持countDocuments()和estimatedDocumentCount()的新API。For the specific API names for a given driver, see the driver documentation.有关给定驱动程序的特定API名称，请参阅驱动程序文档。
Returns the count of documents that would match a 返回与集合或视图的find() query for the collection or view. find()查询匹配的文档数。The db.collection.count() method does not perform the find() operation but instead counts and returns the number of results that match a query.db.collection.count()方法不执行find()操作，而是统计并返回与查询匹配的结果数。
Avoid using the 避免在没有查询谓词的情况下使用db.collection.count() method without a query predicate since without the query predicate, the method returns results based on the collection's metadata, which may result in an approximate count. db.collection.count()方法，因为如果没有查询谓语，该方法将根据集合的元数据返回结果，这可能会导致近似计数。In particular,特别地，
count选项的collStats管道阶段。query | document | |
options | document |
The options document contains the following fields:options文档包含以下字段：
limit | integer | |
skip | integer | |
hint | string or document | |
maxTimeMS | integer | |
readConcern | string |
|
collation | document |
collation: {
locale: <string>,
caseLevel: <boolean>,
caseFirst: <string>,
strength: <int>,
numericOrdering: <boolean>,
alternate: <string>,
maxVariable: <string>,
backwards: <boolean>
}
|
count() is equivalent to the 等效于db.collection.find(query).count() construct.db.collection.find(query).count()构造。
You cannot use 不能在事务中使用count and shell helpers count() and db.collection.count() in transactions.count和shell helpers count()和db.collection.count()）。
For details, see Transactions and Count Operations.有关详细信息，请参阅事务和计数操作。
On a sharded cluster, 在分片集群上，如果存在孤立文档或正在进行区块迁移，则没有查询谓词的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.db.collection.count()可能会导致计数不准确。
To avoid these situations, on a sharded cluster, use the 要避免这些情况，请在分片集群上使用db.collection.aggregate() method:db.collection.aggregate()方法：
You can use the 您可以使用$count stage to count the documents. $count阶段对文档进行计数。For example, the following operation counts the documents in a collection:例如，以下操作对集合中的文档进行计数：
db.collection.aggregate( [
{ $count: "myCount" }
])
The $count stage is equivalent to the following $group + $project sequence:$count阶段相当于以下$group + $project序列：
db.collection.aggregate( [
{ $group: { _id: null, count: { $sum: 1 } } }
{ $project: { _id: 0 } }
] )
$collStats to return an approximate count based on the collection's metadata.根据集合的元数据返回近似计数。
Consider a collection with the following index:考虑具有以下索引的集合：
{ a: 1, b: 1 }
When performing a count, MongoDB can return the count using only the index if:在执行计数时，如果满足以下条件，MongoDB只能使用索引返回计数：
For example, the following operations can return the count using only the index:例如，以下操作只能使用索引返回计数：
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.但是，如果查询可以使用索引，但查询谓词不访问单个连续的索引键范围，或者查询还包含索引外字段的条件，那么除了使用索引外，MongoDB还必须读取文档以返回计数。
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.在这种情况下，在文档的初始读取期间，MongoDB将文档分页到内存中，这样相同计数操作的后续调用将具有更好的性能。
After an unclean shutdown of a 在使用Wired Tiger存储引擎不干净地关闭mongod using the Wired Tiger storage engine, count statistics reported by count() may be inaccurate.mongod后，count()报告的计数统计信息可能不准确。
The amount of drift depends on the number of insert, update, or delete operations performed between the last checkpoint and the unclean shutdown. 漂移量取决于在最后一个检查点和非干净关闭之间执行的插入、更新或删除操作的数量。Checkpoints usually occur every 60 seconds. 检查点通常每60秒进行一次。However, 然而，使用非默认mongod instances running with non-default --syncdelay settings may have more or less frequent checkpoints.--syncdelay设置运行的mongod实例可能有或多或少的检查点频率。
Run 在validate on each collection on the mongod to restore statistics after an unclean shutdown.mongod上的每个集合上运行validate，以在不干净关闭后恢复统计信息。
After an unclean shutdown:不干净停机后：
validate updates the count statistic in the collStats output with the latest value.collStats output are estimates.collStats输出中插入或删除的文档数，都是估计值。This loss of accuracy only applies to 这种精度损失仅适用于不包含查询谓词的count() operations that do not include a query predicate.count()操作。
Starting in MongoDB 4.2, if the client that issued the 从MongoDB 4.2开始，如果发出db.collection.count() disconnects before the operation completes, MongoDB marks the db.collection.count() for termination (i.e. killOp on the operation).db.collection.count()的客户端在操作完成之前断开连接，MongoDB会将db.collection.count()标记为终止（即操作上的killOp）。
To count the number of all documents in the 要计算orders collection, use the following operation:orders集合中所有文档的数量，请使用以下操作：
db.orders.count()
This operation is equivalent to the following:此操作相当于以下操作：
db.orders.find().count()
Count the number of the documents in the 计算orders collection with the field ord_dt greater than new Date('01/01/2012'):orders集合中字段ord_dt大于new Date('01/01/2012')的文档数：
db.orders.count( { ord_dt: { $gt: new Date('01/01/2012') } } )
The query is equivalent to the following:该查询等效于以下内容：
db.orders.find( { ord_dt: { $gt: new Date('01/01/2012') } } ).count()