May be this will useful to you

_sql_constraints = [

('brand_name_uniq', 'unique(field name)', 'Message you want to display')

]

And define after column definition.

Thanks.

Shamji 

I checked the word commented by Pawan "so first delete any duplicate named records" and tried to apply the constraint after deleting all the records in the table with no success, duplicates are still there. Finally I discovered that I have to DROP the table from the database and reinstall the module again so the constraint can go into the table definition. I added this reply for clarification

Hi Robert,

you can create a sql constraint just using unique(name) as:

_sql_constraints = [('name_uniq', 'unique(name)', 'Brand name must be unique!')]

And keep in mind that there should be no duplicate name already existing in the particular master(table), if it exists then the sql contraint will not apply on that master, so first delete any duplicate named records, and then try updating database again.

Thanks
Pawan

So it should be like that:

class product_template(orm.Model):

_inherit = 'product.template'

_sql_constraints = [('brand_uniq',unique('brand'),'Brand name must be unique!'),] # is this correct ? 

_columns = {

'product_brand_id': fields.many2one(

'product.brand',

'Brand', help='Select a brand for this product.', ondelete='restrict'),

}