SPMetal is a great tool, of you don’t know SPMetal it’s an ORM tool that maps SharePoint objects to entity classes, it abstracts all of that CAML ugliness with a nice linq provider and it sort of works nicely. But as with almost everything in SharePoint it has its glitches.
I just come across a pretty nasty one. I have this entity that for some reason one of the fields was always returning null, no custom mappings completely auto-generated like the rest of my entities.
I have checked the generated CAML and the field is part of the viewfields parameter as expected. After a bit of debugging i realised that the internal field name didn’t match the one SPMetal was using to build the CAML. The reason is that apparently SharePoint truncates the internal field name if its length exceeds 32 characters. Now this should be fine but apparently SPMetal developers decided to hardcode the logic of conversion from display to internal, instead of querying the internal name when generating the entities. So a field named “Tools and Websites Link”, will be named internally as “Tools_x0020_and_x0020_Websites_x1”, and SPMetal will generate it as “Tools_x0020_and_x0020_Websites_x0020_Link”. Yep nasty.
There is a couple of solutions here, the most obvious one is to make your field name smaller, bear in mind that if you have spaces in your field name SharePoint replaces them with _x0020_ so if you have a lot of spaces you are guaranteed to hit this limit.
Another workaround is to manually set the internal field name as show in this post.