kyle-eshares

from __future__ import unicode_literals

from django.db import models
from django.db.models.fields.related_descriptors import ForwardManyToOneDescriptor  # noqa


class RelationNotLoaded(Exception):
    pass

kyle-eshares

class conduit(object):
    def __init__(self, iterator):
        self.iterator = iterator

    def filter(self, predicate):
        return conduit(itertools.ifilter(predicate, self.iterator))

    def map(self, func):
        return conduit(itertools.imap(func, self.iterator))

kyle-eshares

"""
Logical deletion for Django models. Uses is_void flag
to hide discarded items from queries. Overrides delete
methods to set flag and soft-delete instead of removing
rows from the database.
"""
from django.apps import apps
from django.contrib.admin.utils import NestedObjects
from django.db import models
from django.db.models import signals

kyle-eshares

from django.db import models

class AppQueryset(models.QuerySet):
    pass

class AppManager(models.Manager):
    queryset_class = AppQuerySet
    
    def get_queryset(self):
        return self.queryset_class(self.model)

kyle-eshares

from django.db import connection

def flatten(*args):
    def transform_pipeline(mdl):
        data = FlatData()
        num_before = len(connection.queries)
        for fn in args:
            fn(data, mdl)
        assert len(connection.queries) == num_before
        return data

kyle-eshares

# 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 = [

kyle-eshares

def is_canceled(report_date)
    def inner(flat, mdl):
        flat.is_canceled = mdl.canceled_date < report_date
    return inner

report_date = datetime.today()

flat_securities = (
  conduit(all_securities)
      .map(

kyle-eshares

Author
------
authors.id | authors.name
-------------------
1         |  "paul"
2         |  "peter"
3         |  "john"

Books
-----

kyle-eshares

>>> Author.objects.count()
20
>>> Book.objects.count()
100
#  This block is 101 queries.
#  1 for the books and 1 for each author that lazy-loaded 
books = Book.objects.all()
for book in books:
   do_stuff(book.title, book.author.name)

kyle-eshares

>> id(author)
4504693520
>>> [(id(book.author), book.author.pk) for book in author.books.all()]
[(4504693520, 1), (4504693520, 1)]