CODEWITHSUNDEEP
djangodjango-queryset
Sam
Sam

Reputation: 133

update a queryset in a specific order

I have a "index" field stores a consequent range of integers, for safety i set it unique.

now I want to increase this field by one, to keep unique I update the value in a descending order:

MyModel.objects.all().order_by('-index').update(index=F('index')+1)

what surprises me is that on some machine an IntegrityError gets raised and complains for duplicated index value.

is there anything i missed? could I only save records one by one?

thanks in advance!

UPDATE:

I think the root problem is that there is no ORDER BY in an SQL UPDATE command (see UPDATE with ORDER BY, and also SQL Server: UPDATE a table by using ORDER BY)

Obviously django simply translates my statement into a SQL UPDATE with ORDER_BY, which leads to an undefined behavior and creates different result per machine.

Upvotes: 1

Views: 709

Answers (1)

Fran Muñoz
Fran Muñoz

Reputation: 154

You are ordering the queryset ascending. You can make it descending by adding the '-' to the field name in the order by:

MyModel.objects.all().order_by('-index').update(index=F('index')+1)

Django docs for order_by

Upvotes: 1

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