$vectorSearch pre filter by null (non existent) properties

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1

When using the $vectorSearch aggregation stage and specifying filter, it doesn’t behave as I expect it would when attempting to filter by null values.

For example, if I specify the filter as either one of these (they’re the same):

{ property: null }

{ property: { $eq: null } }

then the aggregation does not match to any documents that do not have property set.

However, when doing a $match aggregation stage with the same code as above, it matches to documents that do not have property set.

It would be great if we could $vectorSearch filter by properties that do not exist. Is this possible? Otherwise we have to set the property values to null or some other value, and then query based on this value, rather than checking if the property exists or not. This would also mean having to update any existing $match queries that check if the property doesn’t exist.

2

In MongoDB’s $vectorSearch, the filter parameter only matches documents where the indexed field exists with a supported value type; it does not match fields that are missing, so { field: null } won’t catch documents where the field doesn’t exist. To work around this, you can either ensure all documents include the field (even if null) so pre-filtering works, or apply a post-filter $match after $vectorSearch to catch missing or null fields, though this is less efficient since it happens after vector retrieval.