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.. _alembic.runtime.environment.toplevel:
=======================
Runtime Objects
=======================
The "runtime" of Alembic involves the :class:`.EnvironmentContext`
and :class:`.MigrationContext` objects. These are the objects that are
in play once the ``env.py`` script is loaded up by a command and
a migration operation proceeds.
The Environment Context
=======================
The :class:`.EnvironmentContext` class provides most of the
API used within an ``env.py`` script. Within ``env.py``,
the instantiated :class:`.EnvironmentContext` is made available
via a special *proxy module* called ``alembic.context``. That is,
you can import ``alembic.context`` like a regular Python module,
and each name you call upon it is ultimately routed towards the
current :class:`.EnvironmentContext` in use.
In particular, the key method used within ``env.py`` is :meth:`.EnvironmentContext.configure`,
which establishes all the details about how the database will be accessed.
.. automodule:: alembic.runtime.environment
:members: EnvironmentContext
.. _alembic.runtime.migration.toplevel:
The Migration Context
=====================
The :class:`.MigrationContext` handles the actual work to be performed
against a database backend as migration operations proceed. It is generally
not exposed to the end-user, except when the
:paramref:`~.EnvironmentContext.configure.on_version_apply` callback hook is used.
.. automodule:: alembic.runtime.migration
:members: MigrationContext
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