Question

I am probably missing something, but I just cannot understand how MongoDB defines the key ranges, in terms of type.

Say I have a collection for user profiles that look like this:

{userId : "123", profiles: [p1, p2], location: "loc"}

Then if I declare the shard key like this:

{ shardcollection : "test.user_profile", key : {"userId":1} }

How will the ranges work:

1. If userId in {1 … 100000}?
2. If userId is some string, like a generated UUID?

How can I define a shard key that would be treated as string, time md5 or something else?

Answer 1

The comparison on fields in mongo is done according the the BSON comparison order.
See here for more details.
http://www.mongodb.org/display/DOCS/What+is+the+Compare+Order+for+BSON+Types
and here for information on creating specific types
http://www.mongodb.org/display/DOCS/Data+Types+and+Conventions