This is a change that we have submitted a pull request for.

We would like to have the ToLowerInvariant and ToUpperInvariant methods added to the string expressions that the linq that the MongoDB driver recognizes.

We have an OData parser that creates expression trees that use "ToLowerInvariant" and "ToUpperInvariant" methods instead of "ToLower" and "ToUpper." Implementing these methods is a variable small change but makes the driver much more useful to us.