[Twisted-web] Nevow + adbapi

[Matt Goodall]

On Thu, 2005-03-10 at 17:34 -0600, Luis N wrote:
> I must be a total moron:
> 
> I have this:
> 
> def query():
>     return dbpool.runQuery("SELECT english FROM lang WHERE spanish LIKE 'hola'")
> 
> def result(res):
>     if res:
>         print res[0][0]
>     else:
>         print "Failed."
> 
> def words(ctx, data):
>     query().addCallback(result)
> 
> class PData(rend.Page):
>     addSlash=True
>     docFactory = loaders.stan(tags.html[
>         tags.div(data="words")[ words ]])
> 
> And I get this at the terminal, which is correct:
> 
> 2005/03/10 23:30 GMT [HTTPChannel,0,148.241.73.37] 148.241.73.37 - -
> [10/Mar/2005:23:30:09 +0000] "GET / HTTP/1.1" 200 126 "-" "Mozilla/4.0
> (compatible; MSIE 6.0; Windows NT 5.0)"
> 2005/03/10 23:30 GMT [-] hello
> 
> But I get a big red None on the web.

You are not returning the word from the callback chain. The value
returned from a callback chain is the result of the last callback in the
chain. result() needs to return the word if found:

        def result(res):
            if res:
                print res[0][0]
                return res[0][0]
            else:
                print "Failed."

Also, unless you return the deferred from words(), Nevow will not know
it should wait for the deferred to fire:

        def words(ctx, data):
            return query().addCallback(result)


- Matt

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