Peewee : How to update specific fields? - database

Question

I'm using Peewee for working with database. I have a User tables with 3 fields: username, password and last_login. When a user login to the system i want to update last_login. I've use following lines of code:
from peewee import *
import datetime
class User(Model):
username = CharField(unique=True)
password = CharField()
last_login = DateTimeField(default=datetime.datetime.now())
class Meta:
database = MySQLDatabase('mydb', user='root', charset='123456')
u=User(username="user1", last_login=datetime.datetime.now())
u.save()
Although i haven't specified any value for password, it is overwritten after u.save() is called. How should i force peewee to only update last_login field?

Answer 1

Replace u.save() with:
u.save(only=[User.last_login])
As the API's documentation says:
only (list) – A list of fields to persist – when supplied, only the given fields will be persisted.
So you should specify a list of fields you want to be changed.

Answer 2

You can use the only argument when calling save(). http://docs.peewee-orm.com/en/latest/peewee/api.html#Model.save
When a user login to the system i want to update last_login. I've use following lines of code:
If you want to do this, you should do an atomic update, however:
User.update({User.last_login: datetime.datetime.now()}).where(User.username == 'whatever').execute()

Answer 3

The following code will demonstrate how to create, get and update a record in the database:
now = datetime.datetime.now()
# create a user
u = User.create(username="user1", password="bla", last_login=now)
# now `u` has your user, you can do: print u.username, u.password, u.last_login
# get an existing user from the db
u = User.get(User.username == "user1")
print u.username, u.password, u.last_login
sleep(1)
now = datetime.datetime.now()
# update an existing user
u = User.update(password="blabla", last_login=now).where(User.username == "user1")
u.execute()

Answer 4

If you want to save only modified fields, you may use the method below:
class User(Model):
username = CharField(unique=True)
password = CharField()
last_login = DateTimeField(default=datetime.datetime.now())
class Meta:
database = MySQLDatabase('mydb', user='root', charset='123456')
# This method saves only modefied fields
only_save_dirty = True
u=User(username="user1", last_login=datetime.datetime.now())
u.save()