Cannot save record from Django Model - django

Question

I am making a change to a record in a sqlite3 database using Django, and the save() function doesn't seem to work.
I am able to save changes using the graphical admin app however.
Here is the code to the specific model I'm trying to do the save in:
def pickup(self,item):
room_items = Item.objects.filter(roomID = self.room.id)
items = [ri.item_name for ri in room_items]
if item in items:
i = Item.objects.filter(item_name = item)
i[0].roomID = 0
i[0].playerID = self.id
i[0].save()
return f'{self.name} picked up the {item} from {self.room}'
else:
return f"{item} is not in the room. can't pick it up."
the pickup function is in a class called Player. I am updating an Item record. Any solutions?
Here is the entire models file for those who want more context:
from django.db import models
import string,random
class Room(models.Model):
### Field Columns in Room Table ###
room_name = models.CharField(max_length = 64)
description = models.CharField(max_length=500, default=f"No Room description'" )
up = models.CharField(max_length = 64, default="")
down = models.CharField(max_length = 64, default="")
left = models.CharField(max_length = 64, default="")
right = models.CharField(max_length = 64, default="")
def items(self):
items = Item.objects.filter(roomID = self.id)
return [i.item_name for i in items]
def __str__(self):
return self.room_name
class Player(models.Model):
# uuid = models.UUIDField(default=uuid.uuid4, unique=True)
HP = models.IntegerField(default=10)
name = models.CharField(max_length=64, default=f"Room {random.choice(string.ascii_letters)}")#attempting to generate a random room name using ascii_letters from string library and random.choice()
room = models.ForeignKey(Room, on_delete=models.CASCADE, null=True)
# inventory = models.ForeignKey(Inventory)
def inventory(self):
inventory = Item.objects.filter(playerID = self.room.id)
return [i.item_name for i in inventory]
def pickup(self,item):
print(self.room.id)
room_items = Item.objects.filter(roomID = self.room.id)
items = [ri.item_name for ri in room_items]
if item in items:
i = Item.objects.filter(item_name = item)
i[0].roomID = 0
i[0].playerID = self.id
i[0].save()
i[0].persist()
return f'{self.name} picked up the {item} from {self.room}'
else:
return f"{item} is not in the room. can't pick it up."
def drop_item(self,item):
pass
def initialize(self,start):
# start = input(f"{self.name}, you are outside the PyTower. It is a 10 story tower. There is a treasure chest on the top floor. Do you have what it takes to reach the top??? type 'y' to enter Pytower: ")
if start == 'y':
self.room = Room.objects.get(room_name = "Foyer")
print(f"{self.name}, you have now entered the {self.room.room_name}")
return f"{self.name}, you have now entered the {self.room.room_name}"
else:
print(f"{self.name}, when you're ready for Pytower, you may enter!")
return f"{self.name}, when you're ready for Pytower, you may enter!"
print(self.room.description)
print('in room: ', self.room, 'up:',self.room.up, 'down:',self.room.down, 'left:',self.room.left, 'right:', self.room.right)
return self.room
def move(self,way=""):
# print(self.room[way]) #causes error, Room object not subscriptable
# print(way)
# if self.room[way]:
# pass
if way == 'up':
if not self.room.up:
print('you cannot go that way. no rooms there...')
return 'you cannot go that way. no rooms there...'
else:
self.room = Room.objects.get(room_name = self.room.up)
print('in room: ', self.room, 'up:',self.room.up, 'down:',self.room.down, 'left:',self.room.left, 'right:', self.room.right)
return self.room
elif way == 'down':
if not self.room.down:
print('you cannot go that way. no rooms there...')
return 'you cannot go that way. no rooms there...'
else:
self.room = Room.objects.get(room_name = self.room.down)
print('in room: ', self.room, 'up:',self.room.up, 'down:',self.room.down, 'left:',self.room.left, 'right:', self.room.right)
return self.room
elif way == 'left':
if not self.room.left:
print('you cannot go that way. no rooms there...')
return 'you cannot go that way. no rooms there...'
else:
self.room = Room.objects.get(room_name = self.room.left)
print('in room-', self.room, 'up-',self.room.up, 'down-',self.room.down, 'left-',self.room.left, 'right-', self.room.right)
return self.room
elif way == 'right':
if not self.room.right:
print('you cannot go that way. no rooms there...')
return 'you cannot go that way. no rooms there...'
else:
self.room = Room.objects.get(room_name = self.room.right)
print('in room: ', self.room, 'up:',self.room.up, 'down:',self.room.down, 'left:',self.room.left, 'right:', self.room.right)
return self.room
else:
print('you have entered an invalid direction')
return 'you have entered an invalid direction'
def __str__(self):
if not self.room:
return f"{self.name} is outside."
else:
return f"{self.name} in {self.room}"
class Item(models.Model):
item_name = models.CharField(max_length=64)
strength = models.IntegerField(default=5)
item_type = models.CharField(max_length=64,default="weapon")
# playerID = models.ForeignKey(Player, on_delete=models.CASCADE, null=True)
# roomID = models.ForeignKey(Room, on_delete=models.CASCADE, null=True)
playerID = models.IntegerField(blank=True,null=True)
roomID = models.IntegerField(default=1,null=True,blank=True)
def persist(self):
self.save()
def __str__(self):
return self.item_name

Answer 1

To understand why your model isn't saving, you must first understand how querysets are evaluated. Essentially, anytime you iterate over them, or slice them, they will hit the database, however there are caveats to this.
Consider the following abstract example:
def MyModel(models.Model):
column = models.IntegerField()
>>> MyModel.objects.create(column=1)
<MyModel: MyModel object (1)>
>>> queryset = MyModel.objects.all()
Slicing:
>>> queryset[0].column = 2
>>> queryset[0].save()
>>> queryset[0].column
1
In the example above, I took a slice, eg. queryset[0], which hits the database, then immediately took a second slice, to try and save the changes made, which hits the database a second time. Finally, I took a third slice, which hits the database again.
Since the first slice is not the same object as the object I called .save() on, the changes are not reflected in the database. To fix this, simply save a reference to the slice as a variable:
>>> instance = queryset[0]
>>> instance.column = 2
>>> instance.save()
>>> instance.column
2
In this example, I only hit the database twice: once when I call instance = queryset[0], and a second time in instance.save().
Here is the optimized version of your code:
def pickup(self, item_name):
items = Item.objects.filter(item_name=item_name, roomID=self.room.id)
if items:
item = items[0]
item.roomID = 0
item.playerID = self.id
item.save()
return 'message'
return 'no item'