Hi, so if I don't have the error message, then the whole code to put in Studio would be : 

for record in self:
        start_date = datetime.strptime(record.x_studio_start_date, '%Y-%m-%d')
        end_date = datetime.strptime(record.x_studio_end_date, '%Y-%m-%d')
        delta = end_date - start_date
        record.x_studio_expected_no_of_days = delta.days

Why do I have an error message then ?
Is there a change if the format of the date is %d-%m-%Y

Thanks in advance for the help

Hi,

You can try this code while importing the datetimefor record in self:
    if record.x_studio_start_date > record.x_studio_end_date:
        raise ValidationError('Start date should not be greater than the end date.')
    else:
        start_date = datetime.strptime(record.x_studio_start_date, '%Y-%m-%d')
        end_date = datetime.strptime(record.x_studio_end_date, '%Y-%m-%d')
        delta = end_date - start_date
        record.x_studio_expected_no_of_days = delta.days

Hope it helps