Case insensitive sorting in MongoDB

Question

How can I sort a MongoDB collection by a given field, case-insensitively? By default, I get A-Z before a-z.

Answer 1

Update: As of now mongodb have case insensitive indexes:

Users.find({})
  .collation({locale: "en" })
  .sort({name: 1})
  .exec()
  .then(...)

shell:

db.getCollection('users')
  .find({})
  .collation({'locale':'en'})
  .sort({'firstName':1})

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Update: This answer is out of date, 3.4 will have case insensitive indexes. Look to the JIRA for more information https://jira.mongodb.org/browse/SERVER-90

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Unfortunately MongoDB does not yet have case insensitive indexes: https://jira.mongodb.org/browse/SERVER-90 and the task has been pushed back.

This means the only way to sort case insensitive currently is to actually create a specific "lower cased" field, copying the value (lower cased of course) of the sort field in question and sorting on that instead.