find

Command Fields命令字段

The command accepts the following fields:该命令接受以下字段：

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

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

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

Output输出

The command returns a document that contains the cursor information, including the cursor ID and the first batch of documents. 该命令返回包含游标信息的文档，包括游标ID和第一批文档。For example, the following document is returned when run against a sharded collection:例如，在针对分片集合运行时，将返回以下文档：

{
   "cursor" : {
      "firstBatch" : [
         {
            "_id" : ObjectId("5e8e2ca217b5324fa9847435"),
            "zipcode" : "20001",
            "x" : 1
         },
         {
            "_id" : ObjectId("5e8e2ca517b5324fa9847436"),
            "zipcode" : "30001",
            "x" : 1
         }
      ],
      "partialResultsReturned" : true, // Starting in version 4.4
      "id" : NumberLong("668860441858272439"),
      "ns" : "test.contacts"
   },
   "ok" : 1,
   "operationTime" : Timestamp(1586380205, 1),
   "$clusterTime" : {
      "clusterTime" : Timestamp(1586380225, 2),
      "signature" : {
         "hash" : BinData(0,"aI/jWsUVUSkMw8id+A+AVVTQh9Y="),
         "keyId" : NumberLong("6813364731999420435")
      }
   }
}

In addition to the aforementioned find-specific fields, the db.runCommand() includes the following information for replica sets and sharded clusters:除了前面提到的find专有字段外，db.runCommand()还包括复制集和分片集群的以下信息：

• $clusterTime
• operationTime

See db.runCommand() Results for details.有关详细信息，请参阅db.runCommand()结果。

$regex Find Queries No Longer Ignore Invalid Regex查找查询不再忽略无效Regex

Starting in MongoDB 5.1, invalid $regex options options are no longer ignored. 从MongoDB 5.1开始，不再忽略无效的$regex选项。This change makes $regex options more consistent with the use of $regex in the aggregate command and projection queries.此更改使$regex选项与aggregate命令和投影查询中$regex的使用更加一致。

Sessions会话

For cursors created inside a session, you cannot call getMore outside the session.对于在会话内创建的游标，不能在会话外调用getMore。

Similarly, for cursors created outside of a session, you cannot call getMore inside a session.类似地，对于在会话之外创建的游标，不能在会话内部调用getMore。

Transactions事务

find can be used inside multi-document transactions.可以在多文档事务中使用。

• For cursors created outside of a transaction, you cannot call getMore inside the transaction.对于在事务外部创建的游标，不能在事务内部调用getMore。
• For cursors created in a transaction, you cannot call getMore outside the transaction.对于在事务中创建的游标，不能在事务外调用getMore。

Client Disconnection客户端断开连接

Starting in MongoDB 4.2, if the client that issued find disconnects before the operation completes, MongoDB marks find for termination using killOp.从MongoDB 4.2开始，如果发出find的客户端在操作完成之前断开连接，MongoDB会使用killOp标记find终止。

Stable API

When using Stable API V1, the following find command fields are not supported:使用Stable API V1时，不支持以下find命令字段：

• awaitData
• max
• min
• noCursorTimeout
• oplogReplay
• returnKey
• showRecordId
• tailable

Index Filters and Collations索引筛选器和排序规则

Starting in MongoDB 6.0, an index filter uses the collation previously set using the planCacheSetFilter command.从MongoDB 6.0开始，索引筛选器使用之前使用planCacheSetFilter命令设置的排序规则。

Specify a Sort and Limit指定排序和限制

The following command runs the find command filtering on the rating field and the cuisine field. 以下命令在rating字段和cuisine字段上运行find命令筛选。The command includes a projection to only return the following fields in the matching documents: _id, name, rating, and address fields.该命令包含一个projection，只返回匹配文档中的以下字段：_id、name、rating和address字段。

The command sorts the documents in the result set by the name field and limits the result set to 5 documents.该命令按name字段对结果集中的文档进行排序，并将结果集限制为5个文档。

db.runCommand(
   {
     find: "restaurants",
     filter: { rating: { $gte: 9 }, cuisine: "italian" },
     projection: { name: 1, rating: 1, address: 1 },
     sort: { name: 1 },
     limit: 5
   }
)

Override Default Read Concern覆盖默认读取关注

To override the default read concern level of "local", use the readConcern option.要覆盖默认的读取关注级别"local"，请使用readConcern选项。

The following operation on a replica set specifies a read concern of "majority" to read the most recent copy of the data confirmed as having been written to a majority of the nodes.以下对副本集的操作指定了"majority"的读取关注，以读取已确认写入大多数节点的数据的最新副本。

db.runCommand(
   {
     find: "restaurants",
     filter: { rating: { $lt: 5 } },
     readConcern: { level: "majority" }
   }
)

Regardless of the read concern level, the most recent data on a node may not reflect the most recent version of the data in the system.无论读取关注级别如何，节点上的最新数据都可能无法反映系统中数据的最新版本。

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。

A readConcern can be specified for the mongosh method db.collection.find() using the cursor.readConcern() method:可以使用cursor.readConcern()方法为mongosh方法db.collection.find()指定readConcern：

db.restaurants.find( { rating: { $lt: 5 } } ).readConcern("majority")

For more information on available read concerns, see Read Concern.有关可用读取关注的更多信息，请参阅读取关注。

Specify Collation指定排序规则

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，例如字母大小写和重音标记的规则。

The following operation runs the find command with the collation specified:以下操作使用指定的排序规则运行find命令：

db.runCommand(
   {
     find: "myColl",
     filter: { category: "cafe", status: "a" },
     sort: { category: 1 },
     collation: { locale: "fr", strength: 1 }
   }
)

mongosh provides the cursor.collation() to specify collation for a db.collection.find() operation.提供了cursor.collation()，用于指定db.collection.find()操作的排序规则。

Use Variables in let在let中使用变量

To define variables that you can access elsewhere in the command, use the let option.要定义可以在命令的其他地方访问的变量，请使用let选项。

Create a collection cakeFlavors:创建一个集合cakeFlavors：

db.cakeFlavors.insertMany( [
   { _id: 1, flavor: "chocolate" },
   { _id: 2, flavor: "strawberry" },
   { _id: 3, flavor: "cherry" }
] )

The following example defines a targetFlavor variable in let and uses the variable to retrieve the chocolate cake flavor:以下示例在let中定义了targetFlavor变量，并使用该变量检索巧克力蛋糕的风味：

db.cakeFlavors.runCommand( {
   find: db.cakeFlavors.getName(),
   filter: { $expr: { $eq: [ "$flavor", "$$targetFlavor" ] } },
   let : { targetFlavor: "chocolate" }
} )