I figured if I could update the amount field in db.product within the buy 
functiontion just around the same time i'm saving inside the db.sale table 
when purchasing then it should be easy but I am having a really hard time 
identifying only the purchased items by their ids & subtracting their 
quantities from similar items in db.product! 

The code below is able to update the amount in db.product but it updates 
for all products which is not what i want
CODE SAMPLE 1:
for item1 in item1:
            diff=item1.amount-value
            db(db.product.amount).update(amount=diff)

Then i made another desperate attempt with the code below but it is not 
updating anything at all!
for item1 in item1:
            for id, k in session.cart.items():
                if item1.id==k:
                    diff=item1.amount-value
                    db(db.product.amount).update(amount=diff)

Anyone who can do this better please help.

Regards;

Mostwanted

On Thursday, September 5, 2019 at 8:21:56 AM UTC+2, Dave S wrote:
>
>
>
> On Wednesday, September 4, 2019 at 10:59:21 PM UTC-7, mostwanted wrote:
>>
>> I have a website where I am selling items, what I desperately want to 
>> achieve is to be able to show the buyers the remaining number of each item. 
>> I have 2 tables, the table that has all the items being sold & has a field 
>> amount which is the current number of items in stock and the other table 
>> which records sales as customers buy and has a field quantity which is 
>> the quantity of items purchased. After a customer has made a purchase I 
>> want to be able to subtract quantity from amount and have difference 
>> update and be the new value for amount.
>>
>> I wrote some controller code which is not achieving this, it is instead 
>> updating the amount field for all items with the same figure.
>>
>>
>> THE VIEW
>>
>> {{extend 'layout.html'}}
>>
>>     <div class="row">
>> {{for p in products:}}
>>         {{if p.product_type=="Earrings":}}
>> <div class="clothes">
>>     <h4 style="color: #ff69b4;">{{=p.name}}</h4>
>>     <h7 style="color: #ff69b4;">{{=p.amount}} available in stock</h7>
>>     <h5>
>>         <span style="color: aqua; font-weight: 
>> bold;">{{=MoneyFormat(p.price)}}</span>
>>     </h5>
>>     <img class="magnify" src="{{=URL('download',args=p.image)}}" 
>> height="200px"/>
>>     <br />
>>     <span id="{{='item%s'%p.id}}" style="font-weight: bold; color: 
>> red;">{{=session.cart.get(p.id,0)}}</span> in cart - {{=A('add to 
>> cart',callback=URL('cart_callback',vars=dict(id=p.id,action='add')),target='item%s'%p.id,_class='button
>>  pill')}}
>>     <br />
>>     <span style="font-size:12px;font-weight: bold; color: #ff69b4;">Click 
>> the image to enlarge</span>
>> <br />
>> </div>
>> {{pass}}
>>
>> {{pass}}
>>         </div>
>>
>>
>> THE CART_CALLBACK FUNCTION
>>
>>
>> def cart_callback():
>>     id = int(request.vars.id)
>>     if request.vars.action == 'add':
>>         session.cart[id]=session.cart.get(id,0)+1
>>     if request.vars.action == 'sub':
>>         session.cart[id]=max(0,session.cart.get(id,0)-1)
>>     return str(session.cart[id])
>>
>>
>> MY FUNCTION FOR UPDATING AFTER PURCHASES
>>
>> def index():
>>     if not auth.user:
>>         response.flash=T('PLEASE LOG IN FIRST TO BE ABLE TO GET THE MENU AND 
>> BUY')
>>     products = db(db.product).select(orderby=db.product.name)
>>     num=db(db.sale).select()
>>     for n in num:
>>         quantity=n.quantity
>>         if quantity is None:
>>             quantity=0
>>         for p in products:
>>             amount1=p.amount-quantity
>>             db(db.product.amount).update(amount=amount1)
>>     return locals()
>>
>>
>> What should happen is that every time a customer buys whatever number of 
>> items a new figure showing reduction in number of items should be displayed.
>>
>>
>> Regards;
>>
>>
>> Mostwanted
>>
>>
>>
> index() looks like it spends a great deal of time subtracting everything 
> in sales from everything in products.
>
> I think you are recording the product id in the cart.  Are you then (on 
> check-out, I presume) recording the product id in db.sales?
>
> if so , then you don't need the select() on all products.
> Instead, use the product id in each row of db.sales to select the product 
> entry to update.
>
> You probably want a way to identify which rows in db.sales have already 
> been processed (that is, which quantities have already been subtracted from 
> the the available in the corresponding product entry).
>
> /dps
>
>  
>

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