Another clojure web framework - Conjure - has rails like migrations.
What do you do ?
Working with these fragments is real simple. Clutch deserializes the JSON from various couch views into native clojure data structures (maps, vecs, etc). From there i just use multimethods[1] to work out how to handle each fragment at various points (url generation, various aspects of the templating etc). I should note that cgrand created a great little macro for me to make working with enlive and multis easier, http://gist.github.com/432752
The hardest part about migrating the nominal schema is changing the JS for the views. Clutch does support running a clojure view server for couch which i think would actually alleviate a lot of my pain points but I wasn't on the ball when i got started. I store all my views in little JS files in the project and have some shamefully rough clojure scripts to update the views in the DB.
Migrating existing data (which i've only had to do once) is a simple case of writing a map (and or filter) function and running it over all the content and doing a bulk update with couch.
I havent had to do much migration though because i largely ported over my established python/django project.
hopefully that answers your question?
In a traditional DB, one needs to manage addition and deletion of columns, during the development of a project. And one needs to be able to synchronize these database schema changes with the rest of the team. And it is nice to have these as incremental (yes there is the obvious waste of creating a column in one migration and dropping it in the other) Migrations also allow you to do stuff like add indexes etc to your tables and is not just a one-to-one mapping of your objects to the DB.
Which is why migrations (Rails and Django's South) are so extremely helpful during development.
One of the things I that was for something like Linq (Scala has something called squeryl) and you could have your database created from your objects - not optimal, but enough to start with.
FWIW, ease of managing incremental schema is why Drupal (using drush and "Drupal Features" ) is one of the better PHP frameworks.
