How to add unique records to the database, but only for the date that is not yet in the database?

Question

Python

I'm starting to practice with databases, and decided to use the peewee ORM. For training, I decided to create a table with expense records and fields: purchase date, product name (unique field), product price.
The model looks like this:

class BaseModel(Model):
    class Meta:
        database = db

class Purchases(BaseModel):
    purchase_day = CharField()
    product = CharField(unique=True)
    price = FloatField()

The problem is that when adding another date of purchase and the product name matches, they get an error because the product name field is unique.
What should be done in such a case? Remove uniqueness from the "product" field, and check with a query when adding a record, or is there another way?