问题
What are these functions?
Where can I read about how they work?
The CouchDB definitive guide doesn't explain it, weird.
回答1:
From the CouchDB definitive guide:
There are other design document functions that are being introduced at the time of this writing, including _update and _filter that we aren’t covering in depth here. Filter functions are covered in Chapter 20, Change Notifications. Imagine a web service that POSTs an XML blob at a URL of your choosing when particular events occur. PayPal’s instant payment notification is one of these. With an _update handler, you can POST these directly in CouchDB and it can parse the XML into a JSON document and save it. The same goes for CSV, multi-part form, or any other format.
More info on update from the wiki:
http://wiki.apache.org/couchdb/Document_Update_Handlers
来源：https://stackoverflow.com/questions/4952419/filter-and-update-functions-in-couchdb