Expire Data from Collections by Setting TTL通过设置TTL使集合中的数据过期

Expire Documents after a Specified Number of Seconds在指定的秒数后使文档过期

To expire data after a specified number of seconds has passed since the indexed field, create a TTL index on a field that holds values of BSON date type or an array of BSON date-typed objects and specify a positive non-zero value in the expireAfterSeconds field. 若要在索引字段后经过指定秒数后使数据过期，请在包含BSON日期类型值或BSON日期型对象数组的字段上创建TTL索引，并在expireAfterSeconds字段中指定一个非零值。A document will expire when the number of seconds in the expireAfterSeconds field has passed since the time specified in its indexed field. 当expireAfterSeconds字段中的秒数超过其索引字段中指定的时间后，文档将过期。[1]

The TTL index expireAfterSeconds value must be within 0 and 2147483647 inclusive.TTL索引expireAfterSeconds值必须介于0和2147483647之间（包括0和2147463647）。

For example, the following operation creates an index on the log_events collection's createdAt field and specifies the expireAfterSeconds value of 10 to set the expiration time to be ten seconds after the time specified by createdAt.例如，以下操作在log_events集合的createdAt字段上创建一个索引，并指定expireAfterSeconds值10，以将过期时间设置为createdAt指定时间后的10秒。

db.log_events.createIndex( { "createdAt": 1 }, { expireAfterSeconds: 10 } )

When adding documents to the log_events collection, set the createdAt field to the current time:将文档添加到log_events集合时，将createdAt字段设置为当前时间：

db.log_events.insertOne( {
   "createdAt": new Date(),
   "logEvent": 2,
   "logMessage": "Success!"
} )

MongoDB will automatically delete documents from the log_events collection when the document's createdAt value [1] is older than the number of seconds specified in expireAfterSeconds.当文档的createdAt值[1]超过expireAfterSeconds中指定的秒数时，MongoDB将自动从log_events集合中删除文档。

Expire Documents at a Specific Clock Time在特定的时钟时间使文档过期

To expire documents at a specific clock time, begin by creating a TTL index on a field that holds values of BSON date type or an array of BSON date-typed objects and specify an expireAfterSeconds value of 0. 要在特定的时钟时间使文档过期，请首先在包含BSON日期类型值或BSON日期型对象数组的字段上创建TTL索引，然后指定expireAfterSeconds值0。For each document in the collection, set the indexed date field to a value corresponding to the time the document should expire. 对于集合中的每个文档，将索引日期字段设置为与文档到期时间相对应的值。If the indexed date field contains a date in the past, MongoDB considers the document expired.如果索引日期字段包含过去的日期，MongoDB会认为该文档已过期。

For example, the following operation creates an index on the log_events collection's expireAt field and specifies the expireAfterSeconds value of 0:例如，以下操作在log_events集合的expireAt字段上创建索引，并指定expireAfterSeconds值0：

db.log_events.createIndex( { "expireAt": 1 }, { expireAfterSeconds: 0 } )

For each document, set the value of expireAt to correspond to the time the document should expire. 对于每个文档，将expireAt的值设置为与文档到期的时间相对应。For example, the following insertOne() operation adds a document that expires at July 22, 2013 14:00:00.例如，以下insertOne()操作将添加一个在July 22, 2013 14:00:00到期的文档。

db.log_events.insertOne( {
   "expireAt": new Date('July 22, 2013 14:00:00'),
   "logEvent": 2,
   "logMessage": "Success!"
} )

MongoDB will automatically delete documents from the log_events collection when the documents' expireAt value is older than the number of seconds specified in expireAfterSeconds, i.e. 0 seconds older in this case. 当文档的expireAt值早于expireAfterSeconds中指定的秒数时，MongoDB将自动从log_events集合中删除文档，即在这种情况下早0秒。As such, the data expires at the specified expireAt value.因此，数据将在指定的expireAt值处过期。

Indexes Configured Using NaN使用NaN配置的索引

Do not set expireAfterSeconds to NaN in your TTL index configuration.请勿在TTL索引配置中将expireAfterSeconds设置为NaN。

Prior to MongoDB 5.0, when a TTL index has expireAfterSeconds set to NaN, MongoDB logs an error and does not remove any records.在MongoDB 5.0之前，当TTL索引expireAfterSeconds设置为NaN时，MongoDB会记录一个错误，并且不会删除任何记录。

From MongoDB 5.0.0 - 5.0.13 (and 6.0.0 - 6.0.1), NaN is treated as 0. 在MongoDB 5.0.0-5.0.13（和6.0.0-6.0.1）中，NaN被视为0。If a TTL index is configured with expireAfterSeconds set to NaN, all TTL-indexed documents expire immediately.如果TTL索引配置为expireAfterSeconds设置为NaN，则所有TTL索引文档将立即过期。

Starting in MongoDB 5.0.14 (and 6.0.2), the server will not use TTL indexes that have expireAfterSeconds set to NaN.从MongoDB 5.0.14（和6.0.2）开始，服务器将不会使用expireAfterSeconds设置为NaN的TTL索引。

However, there are still some situations which may result in unexpected behavior. 然而，仍有一些情况可能会导致意外行为。Documents may expire:文件可能会过期：

• During an initial sync to an earlier version from MongoDB 5.0.0 - 5.0.13 (or 6.0.0 - 6.0.1).在初始同步到MongoDB 5.0.0-5.0.13（或6.0.0-6.0.1）的早期版本期间。

• When upgrading from an earlier version to MongoDB 5.0.0 - 5.0.13.从早期版本升级到MongoDB 5.0.0-5.0.13时。

• When restoring a collection from a pre-5.0 mongodump into a MongoDB 5.0.0 - 5.0.13 (or 6.0.0 - 6.0.1) instance.将集合从5.0之前的mongodump恢复到MongoDB 5.0.0-5.0.13（或6.0.0-6.0.1）实例时。

To avoid problems, either drop or correct any misconfigured TTL indexes.为避免出现问题，请删除或更正任何配置错误的TTL索引。

function getNaNIndexes() {
  const nan_index = [];

  const dbs = db.adminCommand({ listDatabases: 1 }).databases;

  dbs.forEach((d) => {
    const listCollCursor = db
      .getSiblingDB(d.name)
      .runCommand({ listCollections: 1 }).cursor;

    const collDetails = {
      db: listCollCursor.ns.split(".$cmd")[0],
      colls: listCollCursor.firstBatch.map((c) => c.name),
    };

    collDetails.colls.forEach((c) =>
      db
        .getSiblingDB(collDetails.db)
        .getCollection(c)
        .getIndexes()
        .forEach((entry) => {
          if (Object.is(entry.expireAfterSeconds, NaN)) {
            nan_index.push({ ns: `${collDetails.db}.${c}`, index: entry });
          }
        })
    );
  });

  return nan_index;
};

getNaNIndexes();