Remove all documents form collection?

[Kevin Burton]

This is definitely a simple question but I couldn't find the answer immediately.

I want to remove all documents from a collection and then remove the collection. So I use the shell command :

> db.formDefinition.remove({})

But I get the result back:

WriteResult({ "nRemoved" : 0 })

Which leads me to believe that nothing was removed.

Ideas?

[Wan Bachtiar]

Hi Kevin,

MongoDB should display the number of removed documents. At least in versions: v2.6.11, v3.0.9, and v3.2.3.

Make sure that you execute remove() in the right database i.e. the database that contains the collection you intend to remove.

If you execute remove() in a collection that does not exist it would return nRemoved: 0 

For example:

> db.collection_doesnt_exist.remove({})
WriteResult({ "nRemoved" : 0 })

If you are still having this issue, could you provide the following:

• The MongoDB server version that you are using.
• The output of db.collection.stats() before and after you execute remove().

Regards,

Wan.

​

[Kevin Burton]

Thank you. This is helpful.

Is there a separate command to delete/drop the collection? It doesn't seem that removing all the documents also removes the collection.

Thanks again.

Kevin.

[Wan Bachtiar]

Hi Kevin,

To remove a collection from a database you could use db.collection.drop(). It also removes any indexes associated with the dropped collection.

For reference of all the available collection methods please see Collection Methods.

I would recommend to enrol in a free online course MongoDB University: M102 - MongoDB for DBAs to find out more about MongoDB. The next session starts on 15th March.

Kind regards,

Wan.

​

​

[Kevin Burton]

When I do 'db.collection.drop()', I get a return 'false' and nothing is removed.

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[Wan Bachtiar]

Hi Kevin,

As mentioned in the manual for db.collection.drop(), the command returns false when the collection to drop does not exist.

Note that the word collection in db.collection.drop() is meant to be replaced with your own collection name. So per your example, it’s should be db.formDefinition.drop().
So, the command is actually db.<your collection name>.drop().

Also make sure that you executed db.collection.drop() in the correct database. Check using show collections whether the collection that you are wanting to drop exist in the database you are on. Please see command helpers to see commands such as use <db> or show dbs.

Additionally, please check out the tutorial working with the Mongo Shell

Regards,

Wan.

​

[Kevin Burton]

Thank you. I had a typo in my collection name. All is good.

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