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@jzerbe jzerbe/
Last active Aug 29, 2015

What would you like to do?
PolyModel for ever-more-specific selection information instead of a sparse data model
from google.appengine.ext import ndb
from google.appengine.ext.ndb import polymodel
class SelectionBinder(polymodel.PolyModel):
Base class for selecting content.
All selections are at the binder level or more specific.
# the binder in which the selection resides
binder_id = ndb.StringProperty(indexed=True, required=True)
# last time the entity was put
last_modified = ndb.DateTimeProperty(auto_now=True)
# every selection is for tying some metadata to some content.
# key.urlsafe() representation of Annotation.key
annotation_key = ndb.StringProperty(indexed=True, required=True)
class SelectionDoc(SelectionBinder):
Selecting inside of a particular document.
document_id = ndb.StringProperty(indexed=True, required=True)
class SelectionPage(SelectionDoc)
page_id = ndb.StringProperty(indexed=True, required=True)
class SelectionRegion(SelectionPage):
A region can be a paragraph, chart, some object inside of a page.
region_id = ndb.StringProperty(indexed=True, required=True)
class SelectionText(SelectionRegion):
When the parent region is a paragraph, the user is selecting some text.
start_index = ndb.IntegerProperty(indexed=False, required=True)
end_index = ndb.IntegerProperty(indexed=False, required=True)
class SelectionXY(SelectionRegion):
Put a point over a region at an X/Y offset from the top-left.
Only works with static content.
position_x = ndb.IntegerProperty(indexed=False, required=True)
position_y = ndb.IntegerProperty(indexed=False, required=True)
from google.appengine.ext import ndb
class SparseModel(ndb.Model):
def _prepare_for_put(self):
if self._properties:
# store delete work for after read is done
keys_to_remove = []
for key, value in self._properties.iteritems():
if value is None:
# delete properties with None
for key in keys_to_remove:
del self._properties[key]
# finally dig into nested properties
for prop in self._properties.itervalues():

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commented Aug 10, 2014

instead of dropping all None columns from existence on database put via a hack, one can be smart about instantiating entities at the appropriate specificity and reap the rewards of inheritance

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