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From Gowtham Tamizharasan <>
Subject Capturing UserCtx automatically
Date Wed, 19 Feb 2014 06:54:49 GMT
Hi all,

We want to capture the user details of the person who creates or modifies a
document. Now, I understand that in couch context, even a replication job
is a 'user' that is modifying the DB.

I'd ideally like to just use Changes API. It is almost perfect - except -
we don't see the 'user' in the changes API output.

So, I'm thinking of modifying validate_doc_update erlang function such that
it will extract username from UserCtx and set a "_user" field in the
document. However, this will surely interfere with replication. Am I

While we can "work around" this problem by putting some convention in the
users db (if "replication user" role then don't modify _user). Is this
approach good enough and will this work?

So the modification will have be here, correct?

In couch_db.erl:469: ( )

validate_doc_update(Db, Doc, GetDiskDocFun) ->
    DiskDoc = GetDiskDocFun(),
    JsonCtx = couch_util:json_user_ctx(Db),
    SecObj = get_security(Db),
    try [case Fun(Doc, DiskDoc, JsonCtx, SecObj) of
            % INSERT HACK HERE
            ok -> ok;
            Error -> throw(Error)
        end || Fun <- Db#db.validate_doc_funs],

        throw:Error ->


Another question: Can we use an _ field (like "_user") and will it just
work? Or do I have to modify elsewhere too?

In other words, do I have to explicitly do a transfer_fields? How do I now
ensure _user value gets stored? From what we see, _id is written back like

transfer_fields([{<<"_id">>, Id} | Rest], Doc) ->
    transfer_fields(Rest, Doc#doc{id=Id});

That means, I must invent a way to store the user also? like :

*transfer_fields([{<<"_user">>, User} | Rest], Doc) ->*
*    %My falidation for _User field, *
*    transfer_fields(Rest, Doc#doc{user=User});*

 what about retrieval? how ll my *"_user"* field get stored, and how can i
retrieve it?


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