Phantom Properties

Yet one more interesting Web Service problem reared its head today.  The situation is as follows:

The result of a call to a Web Service method is supposed to be a class. The class contains the elements that, basically, make up a record in a database table.  Because of the way that we structure data access, our data access class returns a DataSet with a matching xsd file.  Once the xsd file had been created, the xsd.exe tool was used to create the class definition.  An instance of the class was then hydrated using the XML format of the DataSet and returned through the web service.

(just for the curious amongst you, our reason for not returning the DataSet itself is that the client is an older version of WebSphere and they don't have easy support for processing returning DataSets.)

Key point coming:  the minOccurs value on at least some of the data elements in the xsd was set to 0.  As a result, for some of the data types (specifically integers, int16 and bytes), additional properties were created.  For example, if there were a property called Status, a public boolean property called StatusSpecified would also be created. 

No problem to this point.  A web method is created with a return value of the class that was generated by xsd.  The method is called and *bam* (picture Emeril at this point), an error gets generated.  The error is the following:

Server was unable to process request. File or assembly name q2k5rmkd.dll, or one of its dependencies, was not found.

The experienced among you will recognize this as a error that occurs when the ASP.NET user doesn't have access to the temporary directory.  But that was not the case here. It is also an error that gets returned when one of the classes used in a web service message has a ReadOnly property.  But a review of the returned class shows that this is not the case either. 

As it turns out, the problem is that the Specified properties (such as StatusSpecified) conflicts with an automatically generated property called, coincidentally, StatusSpecified.  This automatic property is generated when the result set contains a minOccurs clause.  It is used with numeric values to identify those properties that have not been assigned.  It is necessary because numeric variables don't have a 'null' value. But the conflict between the autogen'ed properties and the properties that are created by xsd causes the error message seen above.  The easiest solution is to change the name of the properties included in the xsd.exe generated class to have a name that does not have 'Specified' as the suffix.