问题
I'm trying to understand how CouchDB calculates the revision id for a document. I notice from the source that it's calculated by this bit of code here:
couch_util:md5(term_to_binary([Deleted, OldStart, OldRev, Body, Atts2]))
And I know that if I create a new empty document with no attachments, CouchDB always gives it a revision of 1-967a00dff5e02add41819138abb3284d which, in decimal is <<150,122,0,223,245,224,42,221,65,129,145,56,171,179,40,77>>.
However, if I type the following into the erlang prompt (false for deleted, 0 for OldStart, 0 for OldRev, an empty body and no attachments):
erlang:md5(term_to_binary([false, 0, 0, [], []])).
I always get
<<26,196,244,40,211,149,193,185,214,6,230,61,54,138,62,132>>
back.
So what am I doing wrong here - how can I work out the actual revision that couch generates?
回答1:
After reading the answer to Emit Tuples From Erlang Views In CouchDB I realised that what I was doing wrong was not wrapping the empty proplist for body in a tuple. I'm not sure why couch does that, but that's what the problem was.
erlang:md5(term_to_binary([false, 0, 0, {[]}, []])).
Gives the correct answer
<<150,122,0,223,245,224,42,221,65,129,145,56,171,179,40,77>>
来源：https://stackoverflow.com/questions/5954864/how-does-couchdb-calculate-the-revision-number