處理一個值錯誤

Question

我很難修復一個值錯誤， 'OrderItem' instance needs to have a primary key value before a many-to-many relationship can be used. 我知道我必須做些什麼.add()，但我不知道如何。 這裏是OrderItem model

class OrderItem(SmartModel): 
    order_id = models.CharField(max_length=50,db_index=True) 
    date_added = models.DateTimeField(auto_now_add=True) 
    quantity = models.IntegerField(default=0) 
    item = models.ManyToManyField(Item) 

    class Meta: 
     db_table='order_items' 

     def __unicode__(self): 
      return "%s" % (self.order_id) 

這裏是我的意見做，

def add_to_order(request): 
    postdata = request.POST.copy() 
    #get item slug from post data, return blank if empty 
# item_slug = postdata.get('item_slug','') 
    #get quantity added, return 1 if empty 
    quantity = postdata.get('quantity',0) 
    # fetch the item or return missing page error_message 
    i = get_object_or_404(Item) 
    # get items in order 
    order_items = get_order_items(request) 
    item_in_orders = False 
    # check to see if item is already in order 
    for order_item in order_items: 
     if order_item.item.id == i.id: 
      #update the quantity if found 
      order_item.augment_quantity(quantity) 
      item_in_orders = True 
    if not item_in_orders: 
     # creat and save a new order item 
     oi = OrderItem() 
     oi.item = i 
     oi.quantity = quantity 
     oi.order_id = _order_id(request) 
     oi.save() 

，這裏是回溯：

Traceback: 
File "/home/mats-invasion/projects/f4l/env/local/lib/python2.7/site-packages/django/core/handlers/base.py" in get_response 
    111.       response = callback(request, *callback_args, **callback_kwargs) 
File "/home/mats-invasion/projects/f4l/f4l/live/views.py" in get_category 
    25.   order.add_to_order(request) 
File "/home/mats-invasion/projects/f4l/f4l/cart/order.py" in add_to_order 
    48.  oi.item = i 
File "/home/mats-invasion/projects/f4l/env/local/lib/python2.7/site-packages/django/db/models/fields/related.py" in __set__ 
    832.   manager = self.__get__(instance) 
File "/home/mats-invasion/projects/f4l/env/local/lib/python2.7/site-packages/django/db/models/fields/related.py" in __get__ 
    819.    through=self.field.rel.through, 
File "/home/mats-invasion/projects/f4l/env/local/lib/python2.7/site-packages/django/db/models/fields/related.py" in __init__ 
    536.     raise ValueError("%r instance needs to have a primary key value before a many-to-many relationship can be used." % instance.__class__.__name__) 

Exception Type: ValueError at /menu/ 
Exception Value: 'OrderItem' instance needs to have a primary key value before a many-to-many relationship can be used. 

謝謝。

Answer 1

更新您的視圖代碼以增加新的項目，作爲

if not item_in_orders: 
    # creat and save a new order item 
    oi = OrderItem() 
    oi.quantity = quantity 
    oi.order_id = _order_id(request) 
    oi.save() 
    #save oi first, then add i to item 
    oi.item.add(i)