Btukfyl

I am trying to add some validation into a form.

• Validation 1: quantity_moved should be above 0.


• Validation 2: source and destination must be different


• Validation 3: quantity_moved must be lower than the quantity at source location.

Buggy Code

# NOTE: Overriding the default method

def clean(self):

    cleaned_data = super().clean()

    source = str(cleaned_data['source'])

    destination = str(cleaned_data['destination'])

    quantity_moved = cleaned_data['quantity_moved']

    item = cleaned_data['item']



    # Checking if the source and destination are same

    if destination == source:

        msg = 'エラー：移動先と移動元が同じです。'

        self.add_error('source', msg)

        self.add_error('destination', msg)



    # Checking if the quantity to move is more than the current stock at the source location

    max_qty = ActualStock.objects.filter(item=item, location=cleaned_data['source'])[0].current_stock

    print(">" * 80, max_qty)



    if quantity_moved > max_qty:

        msg = "エラー：移動元に商品の数は足りません。現在, {0}に {1}の数は {2} です。".format(source, item, max_qty)

        self.add_error('quantity_moved', msg)

    return cleaned_data

Now, during testing if i enter same values for both source and destination(both are selected from respective dropdowns which points a same table in DB), I get a KeyError.

Now, if I change the order of the checks that I am performing as shown below, the code works.

Working Code:

# NOTE: Overriding the default method

def clean(self):

    cleaned_data = super().clean()

    source = str(cleaned_data['source'])

    destination = str(cleaned_data['destination'])

    quantity_moved = cleaned_data['quantity_moved']

    item = cleaned_data['item']



    # Checking if the quantity to move is more than the current stock at the source location

    max_qty = ActualStock.objects.filter(item=item, location=cleaned_data['source'])[0].current_stock

    print(">" * 80, max_qty)



    if quantity_moved > max_qty:

        msg = "エラー：移動元に商品の数は足りません。現在, {0}に {1}の数は {2} です。".format(source, item, max_qty)

        self.add_error('quantity_moved', msg)





    # Checking if the source and destination are same

    if destination == source:

        msg = 'エラー：移動先と移動元が同じです。'

        self.add_error('source', msg)

        self.add_error('destination', msg)



    return cleaned_data

Like I said, I managed to fix the bug but do not understand what fixed the bug here. Wondering if someone could shed some light.

From the Django docs:

Note that add_error() automatically removes the field from cleaned_data.

So in your first code sample, if destination equals source, you call add_error on both source and destination, and when you want to get source from cleaned_data as follows:

max_qty = ActualStock.objects.filter(item=item, location=cleaned_data['source'])[0].current_stock

You get a key error because source key was removed from cleaned_data

In your second sample you try to get source before calling add_error on it. You can solve this issue more reliably by changing this line of code

max_qty = ActualStock.objects.filter(item=item, location=cleaned_data['source'])[0].current_stock

To this:

max_qty = ActualStock.objects.filter(item=item, location=source)[0].current_stock