How to filter blog post by extended attributes?

You cannot do this with an API call.  Extended attributes are not filterable and are meant as additional data to be used when you already have the parent object.

Ok Thanks Patrick M. 

I'm trying to sort a list of objects, I tried below code, but it's not working, How to sort a list of objects in velocity?

Velocity is fundamentally a presentation layer, Id suggest you create a plugin to handle this as you will have much more control and flexibility, also the sort you mention above is probably case sensitive re the two 'beechcroft' values