find

sort

Optional. 可选。The projection specification to determine which fields to include in the returned documents. 投影规范，用于确定在返回的文档中包含哪些字段。See Projection and Projection Operators.请参见投影和投影运算符。

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

• $
• $elemMatch
• $slice
• $meta

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

Starting in MongoDB 4.2, 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> }.从MongoDB 4.2开始，除了以下例外，如果命令包含min和/或max字段，则需要hint；如果filter是_id字段{ _id: <value> }上的相等条件，则min和/或max不需要hint。

Optional. 可选。The number of documents to return in the first batch. 第一批中要返回的文档数。Defaults to 101. 默认为101。A batchSize of 0 means that the cursor will be established, but no documents will be returned in the first batch.batchSize为0表示将建立游标，但第一批中不会返回任何文档。

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

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

• mongod log messages, in the attr.command.cursor.comment field.
• Database profiler output, in the command.comment field.
• currentOp output, in the command.comment field.

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）。

Changed in version 4.4..在版本4.4.中更改。

Optional. 可选。The cumulative time limit in milliseconds for processing operations on the cursor. 处理游标操作的累积时间限制（毫秒）。MongoDB aborts the operation at the earliest following interrupt point.MongoDB在下一个中断点最早中止操作。

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

Starting in MongoDB 3.6, the readConcern option has the following syntax: 从MongoDB 3.6开始，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为：

• "local". This is the default read concern level for read operations against the primary and secondaries.这是针对主和辅助的读取操作的默认读取关注级别。
• "available". Available for read operations against the primary and secondaries. 可用于对主要和次要磁盘执行读取操作。"available" behaves the same as "local" against the primary and non-sharded secondaries. "available"与"local"在主要和非分片次要磁盘上的行为相同。The query returns the instance's most recent data.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.仅可用于primary上的读取操作。

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. 特定索引的排除上限。See cursor.max() for details.有关详细信息，请参阅cursor.max()。

Starting in MongoDB 4.2, 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> }.从MongoDB 4.2开始，要使用max字段，该命令还必须使用hint，除非指定的筛选器是_id字段{ _id: <value> }上的相等条件。

Optional. 可选。The inclusive lower bound for a specific index. 特定索引的包含下限。See cursor.min() for details.有关详细信息，请参阅cursor.min()。

Starting in MongoDB 4.2, 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> }.从MongoDB 4.2开始，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> }上的相等条件。

Optional. 可选。An internal command for replaying a replica set's oplog.用于重播副本集oplog的内部命令。

To use oplogReplay, the find field must provide a filter option comparing the ts document field to a timestamp using one of the following comparison operators:要使用oplogReplay，find字段必须提供一个筛选器选项，使用以下比较运算符之一将ts文档字段与timestamp进行比较：

• $gte
• $gt
• $eq

For example, the following command replays documents from the datacapped collection with a timestamp later than or equal to January 1st, 2018 UTC:例如，以下命令以晚于或等于2018年1月1日UTC的时间戳重放data封顶集合中的文档：

{ find: "data",
  oplogReplay: true,
  filter: { ts: { $gte: new Timestamp(1514764800, 0) } } }

Optional. 可选。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.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。

Starting in MongoDB 4.4, if find (or subsequent getMore commands) returns partial results due to the unavailability of the queried shard(s), the output includes a partialResultsReturned indicator field.从MongoDB 4.4开始，如果find（或随后的getMore命令）由于查询的分片不可用而返回部分结果，则输出包括partialResultsReturned指示符字段。

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，但一个或多个分片在随后的getMore命令中不可用，则只有在查询的分片不可用时运行的getMore命令才会在输出中包含partialResultsReturned标志。

Optional.可选。

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

collation 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. 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。For descriptions of the fields, see Collation Document.有关字段的说明，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（请参见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将使用以前版本中使用的简单二进制比较进行字符串比较。

You cannot specify multiple collations for an operation. 不能为一个操作指定多个排序规则。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.例如，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，则不能将一种排序规则用于查找，另一种用于排序。

allowDiskUse

Optional.可选。

Use allowDiskUse to allow MongoDB to use temporary files on disk to store data exceeding the 100 megabyte memory limit while processing a non-indexed ("blocking") sort operation. 使用allowDiskUse允许MongoDB在处理非索引（“阻塞”）排序操作时使用磁盘上的临时文件来存储超过100 MB内存限制的数据。If MongoDB requires using more than 100 megabytes of memory for a blocking sort operation, MongoDB returns an error unless the query specifies allowDiskUse. 如果MongoDB需要使用超过100 MB的内存进行阻塞排序操作，则MongoDB将返回一个错误，除非查询指定allowDiskUse。See Sort and Index Use for more information on blocking sort operations.有关阻塞排序操作的更多信息，请参阅排序和索引使用。

allowDiskUse has no effect if MongoDB can satisfy the specified sort using an index, or if the blocking sort requires less than 100 megabytes of memory.如果MongoDB可以使用索引满足指定的排序，或者如果分块排序需要的内存小于100 MB，allowDiskUse将无效。

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

For more information on memory restrictions for large blocking sorts, see Sort and Index Use.有关大型块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. 指定具有变量列表的文档。This allows you to improve command readability by separating the variables from the query text.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.变量被设置为表达式返回的值，之后无法更改。

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>. 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>。For example: 例如：$$targetTotal.

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。

Starting in 4.4, 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. 从4.4开始，如果由于查询的分片不可用，对分片集合的操作返回部分结果，则cursor文档包含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，要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.请参见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，但一个或多个分片在随后的getMore命令中不可用，则只有在查询的分片不可用时运行的getMore命令才会在输出中包含partialResultsReturned标志。