Within the Project Object Model, the Application object has a method, FieldNameToFieldConstant(), that returns a PjField constant for use by the various SetField() and GetField() methods throughout the object model. More information on the SetField Method (and other associated methods) can be found here.

Unfortunately, when using the PSI, there’s no quick way to lookup the Guid for a field. This can be a problem, since the various CustomFieldsRow objects (Task, Resource, Assignment, and Project) do not include the name of the custom field, only the UID (for an example, look at the ProjectCustomFieldsRow entity in the Project 2007 SDK).

Retrieving custom field information in the PSI is accomplished by using the CustomFields web service. The code below is a class that implements a method to retrieve the Guid of a custom field using the field’s name and entity type. I had to chop the code up a lot because of space constraints, so I apologize for the excessive line breaks. This code assumes that you’ve set up a Web Reference to the CustomFields web service named WebSvcCustomFields.