Django：queryset“丢失”一个值

Question

I have 2 models, one with a list of clients and the other with a list of sales. My intention is to add sales rank value to the clients queryset.

all_clients = Contactos.objects.values("id", "Vendedor", "codigo", 'Nombre', "NombrePcia", "Localidad", "FechaUltVenta")
sales = Ventas.objects.all()

Once loaded I aggregate all the sales per client summing the subtotal values of their sales and then order the result by their total sales.

sales_client = sales.values('cliente').annotate(
    fact_total=Sum('subtotal'))

client_rank = sales_client .order_by('-fact_total')

Then I set the rank of those clients and store the value in a the "Rank" values in the same client_rank queryset.

a = 0
for rank in client_rank:
    a = a + 1
    rank['Rank'] = a

Everything fine up to now. When I print the results in the template I get the expected values in the "client_rank" queryset: "client name" + "total sales per client" + "Rank".

{'cliente': '684 DROGUERIA SUR', 'fact_total': Decimal('846470'), 'Rank': 1}
{'cliente': '699 KINE ESTETIC', 'fact_total': Decimal('418160'), 'Rank': 2}
etc....

The problem starts here

First we should take into account that not all the clients in the "all_clients" queryset have actual sales in the "sales" queryset. So I must find which ones do have sales, assign them the "Rank" value and a assign a standard value for the ones who don´t.

    for subject in all_clients:
    subject_code = str(client["codigo"])
    try:
        selected_subject = ranking_clientes.get(cliente__icontains=subject_code)
        subject ['rank'] = selected_subject['Rank']
    except:
        subject ['rank'] = "Some value"

The Try always fails because "selected_subject" doesn´t seems to hace the "Rank" value. If I print the "selected_subject" I get the following:

{'cliente': '904 BAHIA BLANCA BASKET', 'fact_total': Decimal('33890')}

Any clues on why I´, lossing the "Rank" value? The original "client_rank" queryset still has that value included.

Thanks!

Answer 1

I presume that ranking_clientes is the same as client_rank .

The problem is that .get will always do a new query against the database. This means that any modifications you made to the dictionaries returned in the original query will not have been applied to the result of the get call.

You would need to iterate through your query to find the one you need:

selected_subject = next(client for client in ranking_clientes if subject_code in client.cliente)

Note, this is pretty inefficient if you have a lot of clients. I would rethink your model structure. Alternatively, you could look into using a database function to return the rank directly as part of the original query.