find (database command)（数据库命令）

sort

Optional. The projection specification to determine which fields to include in the returned documents.可选。用于确定返回文档中应包含哪些字段的投影规范。

find() operations on views do not support the following find command projection operators:视图上的find()操作不支持以下find命令投影运算符：

• $
• $elemMatch
• $slice
• $meta

Optional. Index specification. Specify either the index name as a string or the index key pattern. If specified, then the query system will only consider plans using the hinted index.可选。指标规范。将索引名称指定为字符串或索引键模式。如果指定，则查询系统将仅考虑使用提示索引的计划。

With the following exception, hint is required if the command includes the min and/or max fields; hint is not required with min and/or max if the filter is an equality condition on the _id field { _id: <value> }.除了以下例外情况，如果命令包含min和/或max字段，则需要hint（提示）；如filter是_id字段{ _id: <value> }上的相等条件，则min和/或max不需要hint。

Optional. The maximum number of documents that can be returned in each batch of a query result. 可选。每批查询结果中可以返回的最大文档数。By default, the find command has an initial batchSize of the lesser of 101 documents or 16 mebibytes (MiB) worth of documents. 默认情况下，find命令的初始batchSize（批大小）为101个文档或16兆字节（MiB）的文档中的较小值。Subsequent batches have a maximum size of 16 MiB. 后续批次的最大容量为16 MiB。This option can enforce a smaller limit than 16 MiB, but not a larger one. When set, the batchSize is the lesser of batchSize documents or 16 MiB worth of documents.此选项可以强制执行小于16 MiB的限制，但不能强制执行更大的限制。设置后，batchSize是batchSize文档或价值16 MiB的文档中的较小值。

A batchSize of 0 means that the cursor is established, but no documents are returned in the first batch.batchSize为0表示游标已建立，但第一批中没有返回文档。

Unlike the previous wire protocol version, a batchSize of 1 for the find command does not close the cursor.与之前的有线协议版本不同，find命令的batchSize为1不会关闭游标。

singleBatch

Optional.可选。 A user-provided comment to attach to this command. Once set, this comment appears alongside records of this command in the following locations:用户提供了要附加到此命令的注释。设置后，此注释将与此命令的记录一起出现在以下位置：

• mongod log messages日志消息, in the attr.command.cursor.comment field.，在attr.command.cursor.comment字段中。
• Database profiler数据库分析器 output, in the command.comment field.输出，在command.comment字段中
• currentOp output, in the command.comment field.输出，在command.comment字段中。

A comment can be any valid BSON type (string, integer, object, array, etc).注释可以是任何有效的BSON类型（字符串、整数、对象、数组等）。

Any comment set on a find command is inherited by any subsequent getMore commands run on the find cursor.find命令上设置的任何注释都会被find游标上运行的任何后续getMore命令继承。

Optional.可选。

Specifies a time limit in milliseconds. If you do not specify a value for maxTimeMS, operations will not time out. A value of 0 explicitly specifies the default unbounded behavior.指定以毫秒为单位的时间限制。如果不指定maxTimeMS的值，操作将不会超时。值0明确指定默认的无界行为。

MongoDB terminates operations that exceed their allotted time limit using the same mechanism as db.killOp(). MongoDB使用与db.killOp()相同的机制终止超过分配时间限制的操作。MongoDB only terminates an operation at one of its designated interrupt points.MongoDB仅在其指定的中断点之一终止操作。

When specifying linearizable read concern, always use maxTimeMS in case a majority of data bearing members are unavailable. 在指定可线性化的读取关注时，如果大多数数据承载成员不可用，请始终使用maxTimeMS。maxTimeMS ensures that the operation does not block indefinitely and instead returns an error if the read concern cannot be fulfilled.确保操作不会无限期阻塞，如果无法满足读取关注，则返回错误。

Optional.可选。 Specifies the read concern.指定读取关注。

The readConcern option has the following syntax: readConcern选项具有以下语法：readConcern: { level: <value> }

Possible read concern levels are:可能的读取关注级别包括：

• "local". This is the default read concern level for read operations against the primary and secondaries.。这是针对主要和次要读取操作的默认读取关注级别。
• "available". Available for read operations against the primary and secondaries. 。可用于对初级和次级进行读取操作。"available" behaves the same as "local" against the primary and non-sharded secondaries. The query returns the instance's most recent data.对primary和非分片secondary的行为与"local"相同。查询返回实例的最新数据。
• "majority". Available for replica sets that use WiredTiger storage engine.。适用于使用WiredTiger存储引擎的副本集。
• "linearizable". Available for read operations on the primary only.。仅适用于primary上的读取操作。
• "snapshot". Available for multi-document transactions and certain read operations outside of multi-document transactions.。可用于多文档事务和多文档事务之外的某些读取操作。

For more formation on the read concern levels, see Read Concern Levels.有关读取关注级别的更多信息，请参阅读取关注级别。

The getMore command uses the readConcern level specified in the originating find command.getMore命令使用原始find命令中指定的readConcern级别。

Optional.可选。 The exclusive upper bound for a specific index. See cursor.max() for details.特定索引的排除上限。有关详细信息，请参阅cursor.max()。

To use the max field, the command must also use hint unless the specified filter is an equality condition on the _id field { _id: <value> }.要使用max字段，命令还必须使用hint，除非指定的filter（筛选器）是_id字段{ _id: <value> }的相等条件。

Optional.可选。 The inclusive lower bound for a specific index. See cursor.min() for details.特定指数的包容性下限。有关详细信息，请参阅cursor.min()。

To use the min field, the command must also use hint unless the specified filter is an equality condition on the _id field { _id: <value> }.要使用min字段，命令还必须使用hint，除非指定的filter是_id字段{ _id: <value> }的相等条件。

Optional. For queries against a sharded collection, allows the command (or subsequent getMore commands) to return partial results, rather than an error, if one or more queried shards are unavailable.可选。对于针对分片集合的查询，如果一个或多个查询的分片不可用，则允许命令（或后续的getMore命令）返回部分结果，而不是错误。

If find (or subsequent getMore commands) returns partial results because the queried shard(s) aren't available, the find output includes a partialResultsReturned indicator field. 如果find（或后续的getMore命令）由于查询的分片不可用而返回部分结果，则find输出将包含partialResultsReturned指示符字段。If the queried shards are available for the initial find command, but one or more shards become unavailable for subsequent getMore commands, only the getMore commands that run while the shards aren't available include partialResultsReturned in their output.如果查询的分片可用于初始find命令，但一个或多个分片不可用于后续的getMore命令，则只有在分片不可用时运行的getMore指令才会在其输出中包含partialResultsReturned。

Optional.可选。

Specifies the collation to use for the operation.指定用于操作的排序规则。

Collation排序规则 allows users to specify language-specific rules for string comparison, such as rules for lettercase and accent marks.允许用户为字符串比较指定特定于语言的规则，例如字母大小写和重音标记的规则。

The collation option has the following syntax:排序规则选项具有以下语法：

collation: {
   locale: <string>,
   caseLevel: <boolean>,
   caseFirst: <string>,
   strength: <int>,
   numericOrdering: <boolean>,
   alternate: <string>,
   maxVariable: <string>,
   backwards: <boolean>
}

When specifying collation, the locale field is mandatory; all other collation fields are optional. For descriptions of the fields, see Collation Document.指定排序规则时，locale字段是必填的；所有其他排序字段都是可选的。有关字段的描述，请参阅排序规则文档。

If the collation is unspecified but the collection has a default collation (see db.createCollection()), the operation uses the collation specified for the collection.如果未指定排序规则，但集合具有默认排序规则（请参阅db.createCollection()），则操作将使用为集合指定的排序规则。

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.如果没有为集合或操作指定排序规则，MongoDB将使用以前版本中用于字符串比较的简单二进制比较。

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.不能为操作指定多个排序规则。例如，您不能为每个字段指定不同的排序规则，或者如果使用排序执行查找，则不能对查找使用一个排序规则，对排序使用另一个。

allowDiskUse

Optional.可选。

Use this option to override allowDiskUseByDefault for a specific query. You can use this option to either:使用此选项可覆盖特定查询的allowDiskUseByDefault。您可以使用此选项：

• Prohibit disk use on a system where disk use is allowed by default.禁止在默认情况下允许使用磁盘的系统上使用磁盘。
• Allow disk use on a system where disk use is prohibited by default.允许在默认情况下禁止使用磁盘的系统上使用磁盘。

Starting in MongoDB 6.0, if allowDiskUseByDefault is set to true and the server requires more than 100 megabytes of memory for a pipeline execution stage, MongoDB automatically writes temporary files to disk unless the query specifies { allowDiskUse: false }.从MongoDB 6.0开始，如果allowDiskUseByDefault设置为true，并且服务器在管道执行阶段需要超过100兆字节的内存，MongoDB会自动将临时文件写入磁盘，除非查询指定{ allowDiskUse: false }。

For details, see allowDiskUseByDefault.有关详细信息，请参阅allowDiskUseByDefault。

allowDiskUse has no effect if MongoDB can satisfy the specified sort using an index, or if the in-memory sort requires less than 100 megabytes of memory.如果MongoDB可以使用索引满足指定的排序，或者如果内存中的排序需要少于100兆字节的内存，则没有效果。

For more complete documentation on allowDiskUse, see cursor.allowDiskUse().有关allowDiskUse的更完整文档，请参阅cursor.allowDiskUse()。

For more information on memory restrictions for large in-memory sorts, see Sort and Index Use.有关大型内存排序的内存限制的更多信息，请参阅排序和索引使用。

Optional.可选。

Specifies a document with a list of variables. This allows you to improve command readability by separating the variables from the query text.指定一个包含变量列表的文档。这允许您通过将变量与查询文本分离来提高命令的可读性。

The document syntax is:文档语法为：

{
  <variable_name_1>: <expression_1>,
  ...,
  <variable_name_n>: <expression_n>
}

The variable is set to the value returned by the expression, and cannot be changed afterwards.变量设置为表达式返回的值，之后不能更改。

To access the value of a variable in the command, use the double dollar sign prefix ($$) together with your variable name in the form $$<variable_name>. For example: $$targetTotal.要在命令中访问变量的值，请使用双美元符号前缀（$$）和变量名，格式为$$<variable_name>。例如：$$targetTotal。

To use a variable to filter results, you must access the variable within the $expr operator.要使用变量筛选结果，您必须在$expr运算符中访问该变量。

For a complete example using let and variables, see Use Variables in let.有关使用let和变量的完整示例，请参阅在let中使用变量。

Contains the cursor information, including the cursor id and the firstBatch of documents.包含游标信息，包括游标id和文档的firstBatch。

If the operation against a sharded collection returns partial results due to the unavailability of the queried shard(s), the cursor document includes a partialResultsReturned field. 如果对分片集合的操作由于查询的分片不可用而返回部分结果，则cursor（游标）文档将包含partialResultsReturned字段。To return partial results, rather than error, due to the unavailability of the queried shard(s), the find command must run with allowPartialResults set to true. 由于查询的分片不可用，为了返回部分结果而不是错误，find命令必须在allowPartialResults设置为true的情况下运行。See allowPartialResults.请参阅allowPartialResults。

If the queried shards are initially available for the find command but one or more shards become unavailable in subsequent getMore commands, only the getMore commands run when a queried shard or shards are unavailable include the partialResultsReturned flag in the output.如果查询的分片最初可用于find命令，但在后续的getMore命令中有一个或多个分片不可用，则只有在查询的分片不可用时运行getMore命令，并在输出中包含partialResultsReturned标志。