No value for argument ‘on_delete’

I am trying to run some python code, using django, but it is returning that “No value for argument ‘on_delete’ in constructor call”.

from django.db import models
from django.contrib.auth.models import User

class Game(models.Model):
    first_player = models.ForeignKey(User,
                                    related_name="games_first_player")
    second_player = models.ForeignKey(User,
                                    related_name="games_second_player")
    start_time = models.DateTimeField(auto_now_add=True)
    last_active = models.DateTimeField(auto_now=True)


class Move(models.Model):
    x = models.IntegerField()
    y = models.IntegerField()
    comment = models.CharField(max_length=300, blank=True)
    by_first_player = models.BooleanField()


game = models.ForeignKey(Game, on_delete=models.CASCADE)

Answer

Use Following Code

from django.db import models
from django.contrib.auth.models import User

class Game(models.Model):
    first_player = models.ForeignKey(User,on_delete=models.CASCADE,
                                    related_name="games_first_player")
    second_player = models.ForeignKey(User,on_delete=models.CASCADE,
                                    related_name="games_second_player")
    start_time = models.DateTimeField(auto_now_add=True)
    last_active = models.DateTimeField(auto_now=True)


class Move(models.Model):
    x = models.IntegerField()
    y = models.IntegerField()
    comment = models.CharField(max_length=300, blank=True)
    by_first_player = models.BooleanField()