case-insensitive query on mongodb

Question

is there a way to query for a case-insensitive value on mongo without using map/reduce?

Answer 1

Suppose you have document that contains tag field and you want search on it

Tags
{
  tag,
  ...
 }

First option is use regex(but it work slow as @RestRisiko said):

db.tags.find( { "tag" : { "$regex" : "C#", "$options" : "-i" } })

Second option is create another, lower case field( and in mongodb it best way):

Tags
{
  tag,
  tagLower,
  ..
}

And use find as usual:

db.tags.find( { "tagLower" : "c#"})

It will work faster, because above code can use index for search.

Answer 2

You have to normalize the data to be queried. Using a regular expression for case-insensitive search might work as well it won't use indexes. So your only option is to normalize. If you need to preserve the original state then you need to denormalize the data and store the normalized values in a dedicated column of the document.