LINQ Query with a Null Reference Exception

[pueblonative]

Dim strAuthorSearch As String
                strAuthorSearch = "http://isbndb.com/api/authors.xml?access_key=CYGCL3GT&index1=name&value1=" & Me.txtSearchTerm.Text
                Clipboard.SetText(strAuthorSearch)
                xResults = XElement.Load(strAuthorSearch)
                Dim authors = From retwriter In xResults.Descendants("AuthorData") Select AuthorID = xResults.Attribute("person_id").Value, Name = Me.txtSearchTerm.Text

                For Each retwriter In authors
                    strSearchKey = retwriter.AuthorID
                Next
                strURLSearch = strURLSearch & "person_id"
                xResults = Nothing

And on a Search of Mark Twain here's what I get back.

<ISBNdb server_time="2008-12-28T02:16:11Z">
−
<AuthorList total_results="5" page_size="10" page_number="1" shown_results="5">
−
<AuthorData person_id="mark_twain_the_author">
<Name>Mark Twain The Author</Name>
</AuthorData>
−
<AuthorData person_id="twain_mark_a01">
<Name>TWAIN MARK</Name>
</AuthorData>
−
<AuthorData person_id="mark_twain_media">
<Name>Mark Twain Media</Name>
</AuthorData>
−
<AuthorData person_id="bancroft_library_mark_twain_pr">
<Name>Bancroft Library Mark Twain Project</Name>
</AuthorData>
−
<AuthorData person_id="twain_mark">
<Name>Twain, Mark</Name>
</AuthorData>
</AuthorList>
</ISBNdb>

But I'm getting a NullReferenceError

[Hack]

Do you have blank, or empty records, that it could be hitting?

[pueblonative]

Don't think so. Just to be on the safe side I did a Clipboard.SetText with the URL and then brought it up in Firefox. It seemed to be accurate. I was just wondering if I was misspelling something.

[Hack]

I did a Clipboard.SetText with the URL and then brought it up in Firefox. It seemed to be accurate.

So are you having the problem based on the browser you are using (I hate those!)?

[pueblonative]

Don't think so either. The XML I posted up is what I'm getting from the isbndb.com in both Firefox AND directly through my VB app.

[Hack]

Ok.

However, if you are getting a Null exception, that means something is coming back as Null.

You are doing a search on Author Names. That would indicate there is an author name that is Null or one or more of the person_Id pieces of information is Null.

Does this error occur regardless of the author you are doing the search for or only when you do Mark Twain?

[pueblonative]

Regardless. I even just to be on the safe side did a find and replace on all the spaces in the search term. No go.

[Hack]

Lets look at this.

http://isbndb.com/api/authors.xml?access_key=CYGCL3GT&index1=name&value1=" & Me.txtSearchTerm.Text

If you hard code values for "name", "value1" and "txtSearchTerm.Text", do you have any problems running it?

[pueblonative]

Yep, same problem.

[pueblonative]

Yep, same problem.

BTW, here's the documentation on the XML for that site. Maybe it helps.

http://isbndb.com/docs/api/54-authors.html

[richard_deeming]

The problem is in the line:

Select AuthorID = xResults.Attribute("person_id").Value

The xResults variable refers to the root of the document, which doesn't have a "person_id" attribute. Try changing the code to:

Select AuthorID = retwriter.Attribute("person_id").Value

[pueblonative]

Thank you, thank you, thank you! That did the trick.