In MongoDB this is not possible: > db.test.insert({"foo.bar": 1}); Mon Jul 26 14:24:39 JS Error: uncaught exception: can't have . in field names [foo.bar] Aft

In MongoDB this is not possible: > db.test.insert({"foo.bar": 1}); Mon Jul 26 14:24:39 JS Error: uncaught exception: can't have . in field names [foo.bar] After all that's only natural, because the dot notation is supported in queries. For example, consider storing an e-mail in MongoDB: { content: "<p>HTML mail. <img src="cid:1234.0" alt="from attachment"/></p>", attachments: { "1234.0": { some details about the attachment } } } This is not legal, but in this case it's of course easy to work around (have attachments in an array and have the CID as a value instead of a key).