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94 lines
3.0 KiB
Python
94 lines
3.0 KiB
Python
5 years ago
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# sqlalchemy/inspect.py
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# Copyright (C) 2005-2020 the SQLAlchemy authors and contributors
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# <see AUTHORS file>
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#
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# This module is part of SQLAlchemy and is released under
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# the MIT License: http://www.opensource.org/licenses/mit-license.php
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"""The inspection module provides the :func:`_sa.inspect` function,
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which delivers runtime information about a wide variety
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of SQLAlchemy objects, both within the Core as well as the
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ORM.
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The :func:`_sa.inspect` function is the entry point to SQLAlchemy's
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public API for viewing the configuration and construction
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of in-memory objects. Depending on the type of object
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passed to :func:`_sa.inspect`, the return value will either be
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a related object which provides a known interface, or in many
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cases it will return the object itself.
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The rationale for :func:`_sa.inspect` is twofold. One is that
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it replaces the need to be aware of a large variety of "information
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getting" functions in SQLAlchemy, such as
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:meth:`_reflection.Inspector.from_engine`,
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:func:`.orm.attributes.instance_state`, :func:`_orm.class_mapper`,
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and others. The other is that the return value of :func:`_sa.inspect`
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is guaranteed to obey a documented API, thus allowing third party
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tools which build on top of SQLAlchemy configurations to be constructed
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in a forwards-compatible way.
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"""
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from . import exc
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from . import util
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_registrars = util.defaultdict(list)
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def inspect(subject, raiseerr=True):
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"""Produce an inspection object for the given target.
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The returned value in some cases may be the
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same object as the one given, such as if a
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:class:`_orm.Mapper` object is passed. In other
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cases, it will be an instance of the registered
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inspection type for the given object, such as
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if an :class:`_engine.Engine` is passed, an
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:class:`_reflection.Inspector` object is returned.
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:param subject: the subject to be inspected.
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:param raiseerr: When ``True``, if the given subject
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does not
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correspond to a known SQLAlchemy inspected type,
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:class:`sqlalchemy.exc.NoInspectionAvailable`
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is raised. If ``False``, ``None`` is returned.
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"""
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type_ = type(subject)
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for cls in type_.__mro__:
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if cls in _registrars:
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reg = _registrars[cls]
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if reg is True:
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return subject
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ret = reg(subject)
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if ret is not None:
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break
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else:
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reg = ret = None
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if raiseerr and (reg is None or ret is None):
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raise exc.NoInspectionAvailable(
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"No inspection system is "
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"available for object of type %s" % type_
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)
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return ret
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def _inspects(*types):
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def decorate(fn_or_cls):
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for type_ in types:
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if type_ in _registrars:
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raise AssertionError(
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"Type %s is already " "registered" % type_
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)
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_registrars[type_] = fn_or_cls
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return fn_or_cls
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return decorate
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def _self_inspects(cls):
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_inspects(cls)(True)
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return cls
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