NotImplemented error combining distinct with annotate

[John Gateley]

Hello,

Python version: Python 3.7.2
Django version: 2.2.3

I want to combine distinct and annotate(Sum(...)), and get the following error:
NotImplementedError: annotate() + distinct(fields) is not implemented.

To describe: I have a bunch of sales entries like:
'John', 100
'Sam', 50
'John', 200
(the model is a text field for salesperson and an integer field for sales_amount)

I want to write a query like:
res = Sales.objects.distinct('salesperson').annotate(Sum('sales_amount'))
for person in res:
    print('Salesperson %s sold %d dollars' % (person.salesperson, person.sales_amount__count))

I would expect:

Salesperson John sold 300 dollars

Salesperson Sam sold 50 dollars

Instead it generates the above error. Is there a way to do this?

Thank you,

John

[Simon Charette]

Assuming you have a model definition `Salesperson` you could use

Salesperson.object.annotate(

    sales_amount=Sum('sales__sales_amount'),

)

But given you mentioned 'salesperson' is a text field you can do

persons = Sales.objects.values('salesperson').annotate(

    sum_sales_amount=Sum('sales_amount')

)

for person in persons:

    print('Salesperson %s sold %d dollars' % (person['salesperson'], person['sum_sales_amount'])

Note that .values() before annotating a an aggregation function results in a GROUP BY

which should should prefer over using DISTINCT.

Cheers,

Simon

[John Gateley]

Thank you Simon, that worked. -- John

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