python_indexes.py

# computations.py

def add_shareholder_name(shareholder_ix):
    def inner(flat, mdl):
        flat.shareholder_name = shareholder_ix[mdl.shareholder_id]
    return inner

def add_transfered_to_labels(transfered_to_ix):
    def inner(flat, mdl):
        flat.exercised_from_labels = [
            sec.label for sec in transfered_to_ix[mdl.id]
        ]
    return inner

...
# data.py

all_securities = list(Security.objects.filter(company=company).all())
all_shareholders = list(ShareHolders.objects.filter(company=company).all())

# Many to One
shareholder_ix = {sh.pk: sh for shareholder in all_shareholders}
# Reverse foreign key
transfered_to_ix = defaultdict(list)
for security in all_securities:
    if security.transformed_from_id:
        transfered_to_ix[security.transformed_from_id].append(security)

flat_securities = (
  conduit(all_securities)
      ...
      .filter(should_show_security) #  Filter securities since now we grab all of them
      .map(
          flatten(
              ...
              add_shareholder_name(shareholder_ix),
              add_transfered_to_labels(transfered_to_ix)
          )
      )
      ...
)