CODEWITHSUNDEEP
ruby-on-railsruby-on-rails-5mongoid
mltsy
mltsy

Reputation: 7084

'$oid' is an illegal key in MongoDB

I've come across (and been stumped by) this error a couple times in Rails apps, when trying to save some data in a Hash field using MongoID:

'$oid' is an illegal key in MongoDB

I'm not sending any data with a key $oid into the hash, so I can't figure out what is causing it.

Upvotes: 1

Views: 816

Answers (1)

mltsy
mltsy

Reputation: 7084

It turns out the problem is when I use the id field of another object in one of these hashes. The id field of MongoID objects are not strings, they are BSON::ObjectIDs, so if you try to stick them into a hash like this:

ObjectWithHash.update(hash_field: {name: a_name, id: other_object.id})

MongoId will try to convert other_object.id to Hash format, and come up with {"$oid" => "......."}, causing the error to show up.

To solve this, you can first convert it to a string and store that: other_object.id.to_s

Upvotes: 2

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