Hi,

You can use SQL Constraints or Python Constraints to achieve this,

1. SQL Constraints

_sql_constraints = [
    ('name', 'unique (name)', 'The Product already Exists!'),
]

2. Python Constraints

@api.constrains('name')
def _check_name(self):
    if self.name:
        product_rec = self.env['product.template'].search(
            [('name', '=', self.name), ('id', '!=', self.id)])
        if product_rec:
            raise UserError(_('Exists ! Already a product exists with same name'))

Eg: 

https://www.odoo.com/documentation/15.0/developer/howtos/rdtraining/11_constraints.html

Hope it helps,

Kiran K

Hello
I am running this code but I am getting the raise UserError message everytime a product is created having a unique or duplicate name. Could I be missing anything out?

if record.name:
existing_product = env['product.template'].search([('id','!=',record.id),('name','=',record.name)])
if existing_product:
raise UserError("You can't have the same Product Name in Odoo twice! (" + record.name + ")")

Is there something I am doing wrong. I go to your link and do the same code with default_code insted of name and that works fine.

Appreciate in advance

Update: I tried this code and it worked for me.

existing_product = env['product.template'].search([('name','=',record.name)])
if len(existing_product) > 1:
raise UserError("Product already in Odoo. (" + record.name + ")")