MongoDB (at least as in 2.2.0) does not support case insensitive indexes.
The general basic approach is to add an indexed string version of the field to which you want to search, and then string search terms when searching from your application. You can update the search field when your documents are inserted / updated.
A more flexible search may take this by adding a source field to several indexed search terms using stems, stop words and other search strategies.
See also: Full-text search in MongoDB .
You can view or vote in the SERVER-90 feature request ("Case insensitive index") in the MongoDB Problem Tracker.
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