[web2py] request.vars in DAL

[CtrlSoft]

hi i'm little confused with request. 
...
model:

db.define_table('menu',
....
Field('parent',type='integer', requires=IS_EMPTY_OR(IS_IN_DB(db, 'menu.id', 
'%(title)s'))),
Field('title', type='string',label=T('Title')),
Field('content', type='text',label=T('Content')),
Field('menu_type', type='string', default=request.vars.mtype, writable=False
) # it's is posible to pass vars in this mode?

.....
 
)



def menu():
   table = request.args(0)
   mtype = request.vars.mtype
   grid = SQLFORM.grid(db[table].menu_type == mtype,args=request.args[:1])
   return dict(item=grid) 




in view:

 <li><a href="{{=URL('appadmin','menu', args=[db.menu], 
vars={'mtype':'top'})}}">Top Menu</a></li>
 <li><a href="{{=URL('appadmin','menu', args=[db.menu], 
vars={'mtype':'side'})}}">Side Menu</a></li>



 i want to hide row that are 'top' or ''side'', it works on select, but 
when i insert a new row in table(with sqlform.grid),
 i want also to hide in combobox field parent that has 
menu_type=request.vars.mtype



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