db.collection.deleteOne() (mongosh method方法)

Deletion Order删除顺序

db.collection.deleteOne() deletes the first document that matches the filter. Use a field that is part of a unique index such as _id for precise deletions.删除与筛选器匹配的第一个文档。使用唯一索引（如_id）中的字段进行精确删除。

Sharded Collections分片化集合

To use db.collection.deleteOne() on a sharded collection:要在分片集合上使用db.collection.deleteOne()，请执行以下操作：

• If you only target one shard, you can use a partial shard key in the query specification.如果只针对一个分片，则可以在查询规范中使用部分分片键。
• You do not need to provide the shard key or _id field in the query specification, because deleteOne() inherently uses a limit of 1.您不需要在查询规范中提供分片键或_id字段，因为deleteOne()固有地使用1的限制。

Transactions事务

db.collection.deleteOne() can be used inside distributed transactions.可以在分布式事务中使用。

Do not explicitly set the write concern for the operation if run in a transaction. To use write concern with transactions, see Transactions and Write Concern.如果在事务中运行，则不要显式设置操作的写入关注。要对事务使用写关注，请参阅事务和写关注。

Oplog Entries操作日志条目

If a db.collection.deleteOne() operation successfully deletes a document, the operation adds an entry on the oplog (operations log). 如果db.collection.deleteOne()操作成功删除文档，则该操作会在oplog（操作日志）上添加一个条目。If the operation fails or does not find a document to delete, the operation does not add an entry on the oplog.如果操作失败或找不到要删除的文档，则操作不会在oplog上添加条目。

Delete a Single Document删除单个文档

The orders collection has documents with the following structure:orders集合具有以下结构的文档：

db.orders.insertOne(
   {
      _id: ObjectId("563237a41a4d68582c2509da"),
      stock: "Brent Crude Futures",
      qty: 250,
      type: "buy-limit",
      limit: 48.90,
      creationts: ISODate("2015-11-01T12:30:15Z"),
      expiryts: ISODate("2015-11-01T12:35:15Z"),
      client: "Crude Traders Inc."
   }
)

The following operation deletes the order with _id: ObjectId("563237a41a4d68582c2509da") :以下操作将删除_id: ObjectId("563237a41a4d68582c2509da")的订单：

try {
   db.orders.deleteOne( { _id: ObjectId("563237a41a4d68582c2509da") } );
} catch (e) {
   print(e);
}

The operation returns:操作返回：

{ acknowledged: true, deletedCount: 1 }

The following operation deletes the first document with expiryts greater than ISODate("2015-11-01T12:40:15Z")以下操作删除expiryts（过期）时间大于ISODate("2015-11-01T12:40:15Z")的第一个文档。

try {
   db.orders.deleteOne( { expiryts: { $lt: ISODate("2015-11-01T12:40:15Z") } } );
} catch (e) {
   print(e);
}

The operation returns:操作返回：

{ acknowledged: true, deletedCount: 1 }

deleteOne() with a Timeout and Query Variables带超时和查询变量的deleteOne()

The following operation deletes the document that matches the type buy-limit, limit is less that the variable priceThreshold, and sets a time limit of 3 seconds:以下操作删除与类型buy-limit匹配的文档，limit小于变量priceThreshold，并设置3秒的时间限制：

try {
   db.orders.deleteOne(
      { type: "buy-limit" },
      { $expr: { $eq: ["$limit", "$$priceThreshold"] } },
      {
         let: { priceThreshold: 49.00 },
         maxTimeMS: 3000
      }
   );
} catch (e) {
   print(e);
}

The operation returns:操作返回：

{ acknowledged: true, deletedCount: 1 }

deleteOne() with Write ConcerndeleteOne()与写入关注

Given a three member replica set, the following operation specifies a w of majority, wtimeout of 100:给定一个由三个成员组成的副本集，以下操作指定w为majority，wtimeout为100：

try {
   db.orders.deleteOne(
       { _id: ObjectId("563237a41a4d68582c2509da") },
       { w: "majority", wtimeout: 100 }
   );
} catch (e) {
   print (e);
}

If the acknowledgment takes longer than the wtimeout limit, the following exception is thrown:如果确认时间超过wtimeout限制，则抛出以下异常：

WriteConcernError({
   code: 64,
   errmsg: "waiting for replication timed out",
   errInfo: {
     wtimeout: true,
     writeConcern: {
       w: "majority",
       wtimeout: 100,
       provenance: "getLastErrorDefaults"
     }
   }
})

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.排序规则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。

A restaurants collection has the following documents:restaurants集合有以下文件：

db.restaurants.insertMany( [
   { _id: 1, category: "café", status: "Open" },
   { _id: 2, category: "cafe", status: "open" },
   { _id: 3, category: "cafE", status: "open" }
] )

The following operation includes the collation option:以下操作包括collation选项：

db.restaurants.deleteOne(
   { category: "cafe", status: "Open" },
   { collation: { locale: "fr", strength: 1 } }
)

The delete filter specifies a collation with strength: 1, which means the collation ignores differences between case and letter variants. 删除筛选器指定了一个strength: 1的排序规则，这意味着排序规则忽略了大小写和字母变体之间的差异。As a result, even though there is not a document that has an exact match with the specified case and letter variants in the filter, the operation still matches and deletes a document.因此，即使没有与筛选器中指定的大小写和字母变体完全匹配的文档，该操作仍然会匹配并删除文档。

Specify hint for Delete Operations指定删除操作的hint

In mongosh, create a students collection with the following documents:在mongosh中，使用以下文档创建一个students集合：

db.members.insertMany( [
   { _id: 1, student: "Richard", grade: "F", points: 0 },
   { _id: 2, student: "Jane", grade: "A", points: 60 },
   { _id: 3, student: "Adam", grade: "F", points:  0 },
   { _id: 4, student: "Ronan", grade: "D", points: 20 },
   { _id: 5, student: "Noah", grade: "F", points:  0 },
   { _id: 6, student: "Henry", grade: "A", points: 86 }
] )

Create the following index on the collection:在集合上创建以下索引：

db.members.createIndex( { grade: 1 } )

The following delete operation explicitly hints to use the index { grade: 1 }:以下删除操作明确提示使用索引{ grade: 1 }：

db.members.deleteOne(
   { points: { $lte: 20 }, grade: "F" },
   { hint: { grade: 1 } }
)

The delete command returns the following:delete命令返回以下内容：

{ acknowledged: true, deletedCount: 1 }

To view the indexes used, you can use the $indexStats pipeline:要查看使用的索引，可以使用$indexStats管道：

db.members.aggregate( [ { $indexStats: { } }, { $sort: { name: 1 } } ] )

The accesses.ops field in the $indexStats output indicates the number of operations that used the index.$indexStats输出中的accesses.ops字段指示使用索引的操作数。