CODEWITHSUNDEEP
mongodb
weird_coder
weird_coder

Reputation: 213

Auto deletion of documents from mongodb after specified time

I want to auto delete documents from a collection in mongodb based on a ttl. I have gone through other answers and figured out the following way:

db.collection.createIndex( { "createdAt": 1 }, { expireAfterSeconds: 3600 } )

This will delete the documents after expireAfterSeconds interval from createdAt field.

However, the problem with above is that it is not document specific. In the above scenario, all documents will be deleted after 3600 time from creation. However, in my case, each document in the collection needs to be deleted at different time intervals. So, each document need to have its own ttl. How can I achieve this?

Upvotes: 21

Views: 30406

Answers (2)

György Gulyás
György Gulyás

Reputation: 1598

You have to add an new filed to to you collection like: expiresAt, and fill the document expiration date for each document individually. This field is independent from createdAt.

After create an index for new field:

db.collection.createIndex( { "expiresAt": 1 }, { expireAfterSeconds: 0 } )

Upvotes: 1

Joel Lord
Joel Lord

Reputation: 2173

The TTL index will remove all the documents that are older than the indexed field + the expireAfterSeconds values.

Take the following example (using mongosh).

Start by creating 10 documents that have a "expiresAt" field that will be within 10 minutes of now.

for (let i = 0; i < 10; i ++) {
  let expiresAt = new Date();
  expiresAt.setMinutes(expiresAt.getMinutes() + Math.round(Math.random() * 10));
  db.ttl.insertOne({expiresAt})
}

If you create your TTL index

db.ttl.createIndex( { "expiresAt": 1 }, { expireAfterSeconds: 1 } );

If you wait 5 minutes, (statistically ;) ) half of your documents should have been deleted. If you waited another 5 minutes, all of them should be gone. However if you update the expiresAt field.

let newExpiresAt = new Date();
newExpiresAt.setMinutes(newExpiresAt.getMinutes() + 10);
db.ttl.updateMany({}, {expiresAt: newExpiresAt})

Your documents won't expire for another 10 minutes.

More on the TTL indexes in the docs

Upvotes: 1

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