Custom Fields Query Error

Hi, on Appcelerator Cloud I have some place data with custom_fields of 'category'

Im trying to be able to query places with specific 'category'(which are custom_field) and show it as a list.

I read through the documentations on query and custom_fields and wrote the code as below but it does not work.

Cheers in advance,

var categoryselected = picker.getSelectedRow(0).title;
    Cloud.Places.query({
            page: 1,
            per_page: 10,
            where: {
                category: categoryselected
            }

Also, I have a table showing list of results from cloud and if anyone can give me a tips on how to 'filter' them, that would be great. Thanks

Ed