MongoDB Differentiates Between undefined vs. null

Question

I was checking logic for querying on non-values and noticed when using the mongo shell, it differentiates between undefined and null v

Answer 1

In case you wonder, why MongoDB casts undefined to null instead of just ignoring such properties - ignoreUndefined flag could solve this behaviour.

https://mongodb.github.io/node-mongodb-native/2.1/reference/connecting/connection-settings/

Answer 2

You should be using $exists to check for values that don't have the field.

Answer 3

If you want to return a document where a field exists AND is not null, use { a : {$ne : null}}

Undefined and null values are different, but the shell shows them both as null - https://jira.mongodb.org/browse/SERVER-6102