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At the Forge - Creating Mashups

Issue 147

From Issue #147
July 2006

Jul 01, 2006  By Reuven M. Lerner
 in
It's a crime not to mashup two or more Web services to deliver more than they can deliver separately.
Conclusion

Creating mashups, combinations of existing Web services, can be a great deal of fun, and can make it easier to see patterns in data by putting them on a map. It requires that you have a good understanding of the underlying technologies and their quirks—but with a bit of work, you'll see that creating such mashups can be fun and exciting, and even entertaining. Moreover, as the Web becomes increasingly interconnected, and as applications continue to blur the distinction between the desktop and the Web, we should expect to see more of such mashups, rather than fewer of them.

Resources for this article: /article/9013.

Reuven M. Lerner, a longtime Web/database consultant, is currently a PhD student in Learning Sciences at Northwestern University in Evanston, Illinois. He and his wife recently celebrated the birth of their son Amotz David.

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crime mashup

GFL's picture
Submitted by GFL (not verified) on Tue, 06/06/2006 - 22:07.

Another crime mashup for you:
http://www.newhavencrimelog.org/

Error

cbier's picture
Submitted by cbier on Wed, 05/31/2006 - 21:58.

I get this error when I try to run the code from listing 3:

undefined method `text' for nil:NilClass
(
NoMethodError
)

The error is from this line:

next if geocoder_xml.root.nil?

Thanks for writing great articles. At the Forge is one of my favorite articles.

Error

Reuven Lerner's picture
Submitted by Reuven Lerner on Wed, 06/28/2006 - 01:08.

Hi, cbier. Sorry that it took a while to respond, but I only realized recently that people were asking questions of me on this forum!

The error message tells us that we're trying to invoke a method -- the "text" method -- on nil. Now, we obviously don't have a literal nil in the code, so that means our variable must have a nil value, and we're trying to invoke an unknown method on it.

My guess, and I can't prove it, is that Amazon gave you back a city for which there wasn't any geocoder information. (Maybe the city name was spelled incorrectly?) Thus you got nil back. But then you tried to invoke a method on it. Where? I'm not sure, but I'm guessing that we needed to do a bit more testing -- checking that geocoder_response wasn't nil, and that geocoder_xml wasn't nil, either.

Reuven
Senior Columnist, Linux Journal

Senior Columnist, Linux Journal

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