Recently I needed to delete some documents that I saved in MongoDB after some time. I can think of a few examples of why we would want to delete data after some time: logs / events api keys / access tokens non-active users etc We could do it by running a cronjob that deletes the data, delete the data every time we insert new data or any other solution. Luckily for me, my wife told me that MongoDB already has that mechanism built-in. TTL index TTL (Time-To-Live) indexes are special single-field indexes that MongoDB can use to automatically remove documents from a collection after a certain amount of time. A background thread in MongoDB reads the values in the index and removes expired documents from the collection (usually every minute). For example, to create a TTL index on the field of the collection, use the following operation in the mongo shell: lastModifiedDate eventlog db.eventlog.createIndex( { : }, { : } ) "lastModifiedDate" 1 expireAfterSeconds 3600 The indexed field must be or an array of BSON dates BSON date type If the indexed field in a document is not a date or an array that holds a date value(s), the document will not expire. If a document does not contain the indexed field, the document will not expire. Conditional delete As of MongoDB 3.2, a collection can be partially indexed using a specified filter expression, . TTL index can also be used with partial indexes. partialFilterExpression For example: Delete documents that created 1 hour ago if equals to state TMP db.eventlog.createIndex( { : }, { : , : { : } } ); created_at 1 expireAfterSeconds 3600 partialFilterExpression state 'TMP' Delete documents that created 1 day ago if is lower than count 5 db.eventlog.createIndex( { : }, { : , : { : { : } } } ); created_at 1 expireAfterSeconds 86400 partialFilterExpression count $lt 5 Additional info on partial indexes Real-world example Recently I finished developing , which is a free tool that helps you monitor your apps bundle size. BundleMon One of the components in BundleMon is a service that saves historic reports in order to compare bundle size between branches. So when you open a PR, BundleMon saves a record with the current bundle size report. No need to save the report for more than 30 days, so I just added a TTL index: db.reports.createIndex( { : }, { : , : { : { : } } } ); creationDate 1 expireAfterSeconds 2592000 partialFilterExpression prNumber $exists true Also published at https://dev.to/lironer/delete-expired-documents-automatically-with-mongodb-ttl-index-l44
