FLASK-ADDING DATETIME CALCULATION INTO DATABASE - datetime

Question

I m trying to perform a little calculation and Logic on date.time with Flask application.
1.) the application will calculate the difference between issue date and expiry date called "remaining days" , The application will check if remaining days is less than 365 days and trigger a function
I attempted the first logic to manipulate the data and submit to database
`#bp.route('/cerpacs/add', methods=['GET', 'POST'])
#login_required
def add_cerpac():
"""
Add a an Cerpac/ expartriates to the database
"""
check_admin()
add_cerpac = True
form =CerpacForm()
if form.validate_on_submit():
cerpac = Cerpac(cerpac_serial_no=form.cerpac_serial_no.data,
cerpac_issue_date= form.cerpac_issue_date.data,
cerpac_exp_date=form.cerpac_exp_date.data,
employee =form.employee.data, )
form.cerpac_issue_date.data = cerpac.cerpac_issue_date
form.cerpac_exp_date.data = cerpac.cerpac_exp_date
if request.method == 'POST':
todays_date = datetime.now()
t = cerpac.cerpac_issue_date
t1 = cerpac.cerpac_exp_date
remaining_days = t1 - t
print(remaining_days) - good prints my result!
remaining_days = cerpac.remaining_days ----not adding to database
try:
add cerpac to the database
db.session.add(cerpac)
db.session.commit()
flash('You have successfully added a Cerpac.' )`
`
my model:
class Cerpac(db.Model):
__tablename__ = 'cerpacs'
id = db.Column(db.Integer, primary_key=True)
cerpac_issue_date = db.Column(db.DateTime)
cerpac_exp_date=db.Column(db.DateTime)
remaining_days = db.Column(db.DateTime)
cerpac_serial_no = db.Column(db.String(60))
cerpac_upload = db.Column(db.String(20), default='cerpac.jpg')
renew_status = db.Column(db.Boolean, default=False)
process_status = db.Column(db.Boolean, default=False)
renewcerpac_id = db.Column(db.Integer, db.ForeignKey('renewcerpacs.id'))
employee_id = db.Column(db.Integer, db.ForeignKey('employees.id'))
def __repr__(self):
return '<Cerpac {}>'.format(self.name) model:
I want to add this to database and eventually write a function like this:
I had a mistake also in the code because I had error issue_date not defined. How do I define issue_date as a date.time variable?
def remaining_days(issue_date, expired_date):
issue_date = datetime(issue_date)
days_to_go = expired - issue
if days_to_go == 365:
renew_status== True
print("time to renew")
print("We are Ok")

Answer 1

I would simplify this to something like:
from datetime import datetime
class Cerpac(db.Model):
...
cerpac_exp_date=db.Column(db.DateTime)
...
#property
def remaining_days(self):
return (self.cerpac_exp_date - self.cerpac_issue_date).days
#property
def days_to_expiry(self):
return (self.cerpac_exp_date - datetime.now()).days
Then, days_to_expiry and remaining_days become properties calculated when you query, and update automatically when they renew their cards.