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From "Paul Joseph Davis (JIRA)" <j...@apache.org>
Subject [jira] Commented: (COUCHDB-336) Would like errors in map function to be reported to client
Date Tue, 28 Apr 2009 17:11:30 GMT

    [ https://issues.apache.org/jira/browse/COUCHDB-336?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12703745#action_12703745
] 

Paul Joseph Davis commented on COUCHDB-336:
-------------------------------------------

Chris Anderson had a patch that he was working on for this specifically. IIRC, his behavior
was to throw an error at query time that reports the first error that was thrown from the
map function. Not sure on the current status.

> Would like errors in map function to be reported to client
> ----------------------------------------------------------
>
>                 Key: COUCHDB-336
>                 URL: https://issues.apache.org/jira/browse/COUCHDB-336
>             Project: CouchDB
>          Issue Type: Wish
>         Environment: svn trunk 0.10.0a768591
>            Reporter: Brian Candler
>            Priority: Minor
>
> At the moment, if a runtime error occurs in a map function, the document is silently
excluded from the view and the client is none the wiser.
> $ curl -X PUT http://127.0.0.1:5984/test
> {"ok":true}
> $ curl -d '{"foo":"bar"}' -X PUT http://127.0.0.1:5984/test/doc1
> {"ok":true,"id":"doc1","rev":"1-3413565576"}
> $ curl -d '{"food":"bar"}' -X PUT http://127.0.0.1:5984/test/doc2
> {"ok":true,"id":"doc2","rev":"1-2088327893"}
> # Example 1: map function calls undefined function
> $ curl -d '{"map":"function(doc) { emitt(null,null); }"}' -H 'Content-Type: application/json'
-X POST http://127.0.0.1:5984/test/_temp_view
> {"total_rows":0,"rows":[]}
> # Example 2: map function attempts to emit 'undefined'
> $ curl -d '{"map":"function(doc) { emit(doc._id,doc.foo); }"}' -H 'Content-Type: application/json'
-X POST http://127.0.0.1:5984/test/_temp_view
> {"total_rows":1,"offset":0,"rows":[
> {"id":"doc1","key":"doc1","value":"bar"}
> ]}
> Of course, errors are available in the server log:
> [Tue, 28 Apr 2009 08:40:39 GMT] [info] [<0.1276.0>] OS Process Log Message: function
raised exception (ReferenceError: emitt is not defined) with doc._id doc1
> [Tue, 28 Apr 2009 08:43:44 GMT] [info] [<0.1276.0>] OS Process Log Message: function
raised exception (Cannot encode 'undefined' value as JSON) with doc._id doc2
> But the client cannot see these, and worse, gets what appears to be a valid result set.
> I think there are two cases to consider.
> - in temporary views, it ought to be easy to do something: e.g. (1) return the full set
of failed docs with their errors, or (2) return a count of failed docs, or (3) just abort
on the first error
> - in permanent views, it might also be useful to return this information, but it could
be expensive to persist. Also, when you're querying for key X you might not want to see a
whole load of errors for unrelated docs. An error count might be OK though, similar to total_rows.
> The current behaviour may be useful, although I personally wouldn't want to rely on it,
especially as it generates errors in the log. That is, I would rather be forced to rewrite
example 2 as
>   function(doc) { if (doc.foo) { emit(doc._id, doc.foo); } }
> or
>   function(doc) { emit(doc._id, doc.foo || null); }
> as appropriate.
> Workaround: users can manually wrap each of their map functions in a catcher which emits
a sentinel key/value pair containing the error. However they would still have to query the
key range which includes the error messages.

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