How to query: Array does not contain (case insensitive) element

Question

I'm trying to retrieve documents where the tags array does not contain an element ignoring case sensitivity.

I'm using the inverse of my array contains query:

.find({"tags":{"$regex": "^(?!someTag$)", "$options": "i"}})

However this returns also returns documents where there's a tag that isn't "someTag".

There's a operator called `$nin` that can help you. https://docs.mongodb.com/manual/reference/operator/query/nin/ — igorkf, May 05 '20 at 17:00
@igorkf that would've been the solution if it wasn't for the case insensitivity — Viktor Baert, May 05 '20 at 17:06
Maybe this helps: `db.collection.find( { $text: { $search: "-someTag", $caseSensitive: false } } )` — igorkf, May 05 '20 at 17:10

score 0 · Answer 1 · answered May 05 '20 at 21:03

You can get array does not include behavior with the not equal $ne operator, and case insensitivity with a collation.

Consider a collection with several tags:

> db.coll.find({},{_id:0})
{ "tags" : [ "Tag1", "Tag2", "Tag3" ] }
{ "tags" : [ "tag1", "tag2", "tag3" ] }
{ "tags" : [ "TAG4", "TAG3", "TAG5" ] }
{ "tags" : [ "tag4", "tag6", "tag7" ] }

$ne can be used to exclude exact matches:

> db.coll.find({tags:{$ne:"tag3"}},{_id:0})
{ "tags" : [ "Tag1", "Tag2", "Tag3" ] }
{ "tags" : [ "TAG4", "TAG3", "TAG5" ] }
{ "tags" : [ "tag4", "tag6", "tag7" ] }

With the addition of a collation, the $ne match can be case insensitive:

> db.coll.find({tags:{$ne:"tag3"}},{_id:0}).collation({locale:"en",strength:1})
{ "tags" : [ "tag4", "tag6", "tag7" ] }

Note that in order to use an index with this query, you will need to create an appropriate index with the same collation.

score 0 · Answer 2 · answered May 06 '20 at 09:08

0

Answer provided by a colleague:

Adding a simple $not does the trick.

.find({"tags": {"$not": {"$regex": "^(?!someTag$)", "$options": "i"}}},{"tags":1})

answered May 06 '20 at 09:08

Viktor Baert

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How to query: Array does not contain (case insensitive) element

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