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Delete Documents

Overview

在本指南中，您可以学习如何使用C++驱动程序通过执行删除操作从MongoDB集合中删除文档。

删除操作可从 MongoDB 集合中删除一个或多个文档。您可以使用delete_one()或delete_many()方法执行删除操作。

样本数据

The examples in this guide use the restaurants collection in the sample_restaurants database from the Atlas sample datasets. To access this collection from your C++ application, instantiate a mongocxx::client that connects to an Atlas cluster and assign the following values to your db and collection variables:

auto db = client["sample_restaurants"];
auto collection = db["restaurants"];

要学习如何创建免费的MongoDB Atlas 集群并加载示例数据集，请参阅MongoDB 入门指南。

删除操作

您可以通过以下方法执行删除操作：

delete_one()，这会删除与 Atlas Search条件匹配的第一个文档
delete_many()，这会删除与 Atlas Search条件匹配的所有文档

Each delete method requires a query filter document, which specifies the search criteria to determine which documents to select for removal. For more information about query filters, see the Query Filter Documents section in the MongoDB Server manual.

删除一个文档

以下示例使用delete_one()方法删除restaurants集合中name值为"Ready Penny Inn"的文档：

auto result = collection.delete_one(make_document(kvp("name", "Ready Penny Inn")));

删除多个文档

以下示例使用delete_many()方法删除restaurants集合中borough值为"Brooklyn"的所有文档：

auto result = collection.delete_many(make_document(kvp("borough", "Brooklyn")));

自定义删除操作

您可以通过将mongocxx::options::delete_options类的实例作为可选参数传递来修改delete_one()和delete_many()方法的行为。下表描述了您可以在mongocxx::options::delete_options实例中设立的字段：

字段	说明
`collation`	Specifies the kind of language collation to use when sorting results. For more information, see Collation in the MongoDB Server manual.
`write_concern`	Sets the write concern for the operation. For more information, see Write Concern in the MongoDB Server manual.
`hint`	Gets or sets the index to scan for documents. For more information, see the hint statement in the MongoDB Server manual.
`let`	Specifies a document with a list of values to improve operation readability. Values must be constant or closed expressions that don't reference document fields. For more information, see the let statement in the MongoDB Server manual.
`comment`	Attaches a comment to the operation. For more information, see the delete command fields guide in the MongoDB Server manual.

以下示例调用 delete_many() 方法删除restaurants集合中 name 值包含string "Mongo" 的所有文档。它还会设置mongocxx::options::delete_options实例的comment字段，以便为操作添加注释：

mongocxx::options::delete_options opts{};
opts.comment(bsoncxx::types::bson_value::view_or_value{"Deleting Mongo restaurants"});
auto query_filter = make_document(kvp("name", make_document(kvp("$regex", "Mongo"))));
auto result = collection.delete_many(query_filter.view(), opts);

提示

如果前面的示例使用的是 delete_one() 方法而不是 delete_many()，则驱动程序将仅删除name 值包含 "Mongo" 的第一个文档。

返回值

delete_one()和delete_many()方法返回mongocxx::result::delete_result类的实例。该类包含以下成员函数：

result()，返回原始批量写入结果
deleted_count()，返回已删除的文档数

如果查询筛选器与任何文档都不匹配，则驱动程序不会删除任何文档，并且deleted_count为0 。

以下示例调用delete_many()方法来删除除cuisine值为"Greek"的文档。然后，它调用deleted_count()成员函数来打印已删除文档的数量：

auto result = collection.delete_many(make_document(kvp("cuisine", "Greek")));
std::cout << result->deleted_count() << std::endl;

Deleted documents: 111

API 文档

要进一步了解本指南所讨论的任何方法或类型，请参阅以下 API 文档：