如何通过动态查询比较表的2列

Question

Have a requirement in dynamic querying where i would like to compare 2 columns of a table say "column_a" and "column_b" (all columns are strings). The actual columns to compare are decided at run-time.

I'm using kwargs to create a dictionary. But Django assumes that RHS is an absolute value & not a column of the same table. Using F() is an option, but i cant find any documentation of using F() in kwargs.

if i use kwargs = {'predicted_value':'actual_value'} 'actual_value' is used as a literal string instead of column name

How do i use something like: kwargs = {'predicted_value':F('actual_value')} and pass it as Model.objects.filter(**kwargs)

Alternately, is there a way to use F('column') in LHS ? eg Model.objects.filter(F(column1_name) = F(column2_name))

Answer 1

For a non-dynamic filter field, I would use:

from django.db.models import F

Model.objects.filter(some_col=F(kwargs.get('predicted_value')))

But if you need it all dynamically, you can try with:

kwargs = {'predicted_value':F('actual_value')}
Model.objects.filter(**kwargs)

You can even access related fields:

kwargs = {'fk_field__somefield':F('actual_value')}
Model.objects.filter(**kwargs)