Custom classes inheriting Entity cannot be constructed from entities

[ghost]

Currently the following doesn't work:

class Foo(Entity):
    def bar(self):
        """ behavior dependent on internal properties such as _key """
ent = dataset.entity()
baz = Foo(ent)
baz.bar()

This is inconsistent with Entity inheriting dict. Besides style issues, I would think sub-classing Entity would be the preferred way to introduce custom behavior, or enforce an entity schema.

Current workaround is:

class Foo(Entity):
    def __init__(self, ent):
         self._entity = ent
    def bar(self):
         """ behavior dependent on _entity """

[dhermes]

@ebbixby Why do you need to use dataset.entity?

Just use

ent = Foo(dataset=dataset)

and go on your merry way?

The constructor takes:

    def __init__(self, dataset=None, kind=None, exclude_from_indexes=()):
        super(Entity, self).__init__()

It's not typical that a constructor accepts an entity of its own type, though in some cases makes sense.

I am inclined to close this as "Working as Intended" but maybe I am missing something?

FWIW We are always discussing removing Dataset.entity and friends.

[ghost]

My mistake. I meant dataset.get_entity(key)

It would be very desirable to get an entity back from a query or fetch by key and immediately cast it to an object that inherits entity. Right?

[dhermes]

Yes, that does seem more reasonable.

This seems to fall under the umbrella of building an ndb-like ORM built on top of this library.

It's unclear that built-in extensibility should also be at this low-level API. I'm inclined to say it should not and that we are happy to support use-cases like this until ndb-like support is available (or ndb itself).

A change that comes to mind which could make Entity easier to extend. No longer inherit from dict and instead redirect __getitem__ into a data attribute:

class Entity(object):
    def __init__(self, dataset=None, kind=None, exclude_from_indexes=(), data=None):
        self.data = data or {}
    def __getitem__(self, name):
        return self.data[name]

@tseaver WDYT?

[elibixby]

I'm ghost. Just consolidating github accounts.

[elibixby]

Just wanna throw my support behind Entity no longer subclassing dict. As it is currently implemented, Entity is much more like an object with a dict as a value than a dict itself. Perhaps an ent.properties() would be more appropriate?

[tseaver]

I don't get the issue behind subclassing dict: if we do that, we will need to provide most of the equivalent behvior (from collections.abc.MutableMapping) in order to allow folks to use it "like a dict". There isn't anything wrong with having extra state or methods on a class that aren't present in the base.

[dhermes]

Ditto here. Closing since new API (hopefully) reduces friction.