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Removing old doc about entities
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Roman Mogilatov
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Entities
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========
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Current section describes main *Objects* entities and their interaction.
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Providers
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---------
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Providers are strategies of accessing objects.
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All providers are callable. They describe how particular objects will be
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provided. For example:
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.. code-block:: python
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"""`NewInstance` and `Singleton` providers example."""
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from objects.providers import NewInstance
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from objects.providers import Singleton
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# NewInstance provider will create new instance of specified class
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# on every call.
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new_object = NewInstance(object)
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object_1 = new_object()
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object_2 = new_object()
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assert object_1 is not object_2
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# Singleton provider will create new instance of specified class on first call,
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# and return same instance on every next call.
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single_object = Singleton(object)
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single_object_1 = single_object()
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single_object_2 = single_object()
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assert single_object_1 is single_object_2
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Injections
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----------
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Injections are additional instructions, that are used for determining
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dependencies of objects.
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Objects can take dependencies in various forms. Some objects take init
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arguments, other are using attributes or methods to be initialized. Injection,
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in terms of *Objects*, is an instruction how to provide dependency for the
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particular object.
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Every Python object could be an injection's value. Special case is a *Objects*
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provider as an injection's value. In such case, injection value is a result of
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injectable provider call (every time injection is done).
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Injections are used by providers.
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.. code-block:: python
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"""`KwArg` and `Attribute` injections example."""
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import sqlite3
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from objects.providers import Singleton
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from objects.providers import NewInstance
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from objects.injections import KwArg
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from objects.injections import Attribute
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class ObjectA(object):
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"""ObjectA has dependency on database."""
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def __init__(self, database):
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"""Initializer.
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Database dependency need to be injected via init arg."""
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self.database = database
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def get_one(self):
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"""Select one from database and return it."""
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return self.database.execute('SELECT 1').fetchone()[0]
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# Database and `ObjectA` providers.
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database = Singleton(sqlite3.Connection,
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KwArg('database', ':memory:'),
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KwArg('timeout', 30),
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KwArg('detect_types', True),
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KwArg('isolation_level', 'EXCLUSIVE'),
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Attribute('row_factory', sqlite3.Row))
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object_a = NewInstance(ObjectA,
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KwArg('database', database))
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# Creating several `ObjectA` instances.
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object_a_1 = object_a()
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object_a_2 = object_a()
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# Making some asserts.
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assert object_a_1 is not object_a_2
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assert object_a_1.database is object_a_2.database
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assert object_a_1.get_one() == object_a_2.get_one() == 1
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Catalogs
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--------
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Catalogs are named set of providers.
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*Objects* catalogs can be used for grouping of providers by some
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kind of rules. In example below, there are two catalogs:
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``Resources`` and ``Models``.
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``Resources`` catalog is used to group all common application resources like
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database connection and various api clients, while ``Models`` catalog is used
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for application model providers only.
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.. code-block:: python
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"""Catalogs example."""
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import sqlite3
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import httplib
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from objects.catalog import AbstractCatalog
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from objects.providers import Singleton
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from objects.providers import NewInstance
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from objects.injections import KwArg
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from objects.injections import Attribute
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class SomeModel(object):
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"""SomeModel has dependency on database and api client.
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Dependencies need to be injected via init args.
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"""
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def __init__(self, database, api_client):
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"""Initializer."""
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self.database = database
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self.api_client = api_client
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def api_request(self):
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"""Make api request."""
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self.api_client.request('GET', '/')
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return self.api_client.getresponse()
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def get_one(self):
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"""Select one from database and return it."""
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return self.database.execute('SELECT 1').fetchone()[0]
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class Resources(AbstractCatalog):
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"""Resource providers catalog."""
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database = Singleton(sqlite3.Connection,
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KwArg('database', ':memory:'),
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KwArg('timeout', 30),
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KwArg('detect_types', True),
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KwArg('isolation_level', 'EXCLUSIVE'),
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Attribute('row_factory', sqlite3.Row))
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api_client = Singleton(httplib.HTTPConnection,
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KwArg('host', 'example.com'),
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KwArg('port', 80),
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KwArg('timeout', 10))
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class Models(AbstractCatalog):
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"""Model providers catalog."""
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some_model = NewInstance(SomeModel,
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KwArg('database', Resources.database),
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KwArg('api_client', Resources.api_client))
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# Creating `SomeModel` instance.
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some_model = Models.some_model()
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# Making some asserts.
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assert some_model.get_one() == 1
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assert some_model.api_request().status == 200
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