如何将正在创建的具有名称的元素限制到已经具有相同名称的元素的Model？Odoo 12

from odoo import api, fields, models, _

class MyModel(models.Model):
    _name = 'my.model'
    name = fields.Char(string='Name', required=True)

class MyModel(models.Model):
    _name = 'my.model'
    name = fields.Char(string='Name', required=True)

    _sql_constraints = [
        ('name_unique', 'unique(name)', 'Element with this name already exists!')
    ]