[web2py] autocomplete widget does not work

[uooyou]

I am fresh man,  I copy the code from chaper 7 ,

db.define_table('category',Field('name'))
db.define_table('product',Field('name'),Field('category'))
db.product.category.widget = SQLFORM.widgets.autocomplete(
     request, db.category.name, limitby=(0,10), min_length=2)

I have fill the table category some data, but it seem does not work.
Some additional work to do ?  thanks!