计算文档

Overview

在本指南中，您可以学习；了解如何使用MongoDB PHP库来检索集合中文档数量的准确估计数。以下方法对集合中的文档进行计数：

MongoDB\Collection::countDocuments()：返回与查询过滤匹配或存在于集合中的文档的确切数量
MongoDB\Collection::estimatedDocumentCount()：返回集合中的估计文档数

样本数据

本指南中的示例使用 Atlas示例数据集的sample_training数据库中的companies集合。要从PHP应用程序访问权限此集合，请实例化一个连接到Atlas 集群的MongoDB\Client ，并将以下值分配给$collection变量：

$collection = $client->sample_training->companies;

要学习；了解如何创建免费的MongoDB Atlas 群集并加载示例数据集，请参阅Atlas入门指南。

检索准确的计数

使用MongoDB\Collection::countDocuments()方法计算集合中的文档数量。要计算匹配特定搜索条件的文档数量，请将查询过滤传递给countDocuments()方法。

要学习；了解有关指定查询的更多信息，请参阅《指定查询》指南。

对所有文档进行计数

要返回集合中所有文档的计数，请将空查询过滤大量传递给countDocuments()方法，如以下示例所示：

$result = $collection->countDocuments([]);
echo 'Number of documents: ', $result;

Number of documents: 9500

对特定文档进行计数

要返回匹配特定搜索条件的文档计数，请将查询过滤传递给countDocuments()方法。

以下示例计算founded_year字段的值为2010的文档数量：

$result = $collection->countDocuments(['founded_year' => 2010]);
echo 'Number of companies founded in 2010: ', $result;

Number of companies founded in 2010: 33

自定义计数行为

您可以通过传递指定选项值的大量来修改countDocuments()方法的行为。下表描述了可用于自设立计数操作的一些选项：

选项	说明
`collation`	The collation to use for the operation. To learn more, see the Collation section of this page. Type: `array\|object`
`hint`	The index to use for the operation. Type: `string\|array\|object`
`comment`	The comment to attach to the operation. Type: any valid BSON type
`limit`	The maximum number of documents to count. This value must be a positive integer. Type: `integer`
`maxTimeMS`	The maximum amount of time in milliseconds that the operation can run. Type: `integer`
`skip`	The number of documents to skip before counting documents. Type: `integer`
`readPreference`	The read preference to use for the operation. To learn more, see Read Preference in the Server manual. Type: `MongoDB\Driver\ReadPreference`

以下示例使用countDocuments()方法计算number_of_employees字段值为50的文档数量，并指示操作最多计算100结果：

$result = $collection->countDocuments(
    ['number_of_employees' => 50],
    ['limit' => 100],
);
echo 'Number of companies with 50 employees: ', $result;

Number of companies with 50 employees: 100

排序规则

要为操作指定排序规则，请传递 $options大量参数，该参数将 collation 选项设置为操作方法。将 collation 选项分配给配置排序规则规则的大量。

下表描述了可以设立以配置排序规则的字段：

字段	说明
`locale`	(Required) Specifies the International Components for Unicode (ICU) locale. For a list of supported locales, see Collation Locales and Default Parameters in the MongoDB Server manual. Data Type: `string`
`caseLevel`	(Optional) Specifies whether to include case comparison. When set to `true`, the comparison behavior depends on the value of the `strength` field: - If `strength` is `1`, the PHP library compares base characters and case. - If `strength` is `2`, the PHP library compares base characters, diacritics, other secondary differences, and case. - If `strength` is any other value, this field is ignored. When set to `false`, the PHP library doesn't include case comparison at strength level `1` or `2`. Data Type: `bool` Default: `false`
`caseFirst`	(Optional) Specifies the sort order of case differences during tertiary level comparisons. Data Type: `string` Default: `"off"`
`strength`	(Optional) Specifies the level of comparison to perform, as defined in the ICU documentation. Data Type: `int` Default: `3`
`numericOrdering`	(Optional) Specifies whether the driver compares numeric strings as numbers. If set to `true`, the PHP library compares numeric strings as numbers. For example, when comparing the strings "10" and "2", the library uses the strings' numeric values and treats "10" as greater than "2". If set to `false`, the PHP library compares numeric strings as strings. For example, when comparing the strings "10" and "2", the library compares one character at a time and treats "10" as less than "2". For more information, see Collation Restrictions in the MongoDB Server manual. Data Type: `bool` Default: `false`
`alternate`	(Optional) Specifies whether the library considers whitespace and punctuation as base characters for comparison purposes. Data Type: `string` Default: `"non-ignorable"`
`maxVariable`	(Optional) Specifies which characters the library considers ignorable when the `alternate` field is set to `"shifted"`. Data Type: `string` Default: `"punct"`
`backwards`	(Optional) Specifies whether strings containing diacritics sort from the back of the string to the front. Data Type: `bool` Default: `false`

要学习；了解有关排序规则和每个字段可能值的更多信息，请参阅MongoDB Server手册中的排序规则条目。

检索估计计数

您可以通过调用MongoDB\Collection::estimatedDocumentCount()方法来检索集合中文档数量的估计值。该方法根据集合元数据估计文档数量，这可能比执行精确计数更快。

以下示例估计集合中的文档数量：

$result = $collection->estimatedDocumentCount();
echo 'Estimated number of documents: ', $result;

Estimated number of documents: 9500

自定义估计计数行为

您可以通过传递指定选项值的大量作为参数来修改estimatedDocumentCount()方法的行为。下表描述了可在大量中设立的选项：

选项	说明
`comment`	The comment to attach to the operation. Type: any valid BSON type
`maxTimeMS`	The maximum amount of time in milliseconds that the operation can run. Type: `integer`
`readConcern`	The read concern to use for the operation. To learn more, see Read Concern in the Server manual. Type: `MongoDB\Driver\ReadConcern`
`readPreference`	The read preference to use for the operation. To learn more, see Read Preference in the Server manual. Type: `MongoDB\Driver\ReadPreference`
`session`	The client session to associate with the operation. Type: `MongoDB\Driver\Session`

以下示例使用estimatedDocumentCount()方法返回集合中文档数量的估计值，并将操作超时设置为1000毫秒：

$result = $collection->estimatedDocumentCount(['maxTimeMS' => 1000]);
echo 'Estimated number of documents: ', $result;

Estimated number of documents: 9500

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：

后退

指定查询

来年

非重复字段值