Openerp: display many2one fields within form view

[gulo]

there is a field many2one. when i tried to open the tree view of that field it shows empty!here is my field: \[code\] 'classb_id': fields.many2one('class.a', 'Reception', required=True, select=True),\[/code\]in my form view :\[code\] <field name="classb_id"/>\[/code\]I already create some record for class.a but tree view doesn't show any data