You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
853 lines
27 KiB
853 lines
27 KiB
# sql/visitors.py
|
|
# Copyright (C) 2005-2022 the SQLAlchemy authors and contributors
|
|
# <see AUTHORS file>
|
|
#
|
|
# This module is part of SQLAlchemy and is released under
|
|
# the MIT License: https://www.opensource.org/licenses/mit-license.php
|
|
|
|
"""Visitor/traversal interface and library functions.
|
|
|
|
SQLAlchemy schema and expression constructs rely on a Python-centric
|
|
version of the classic "visitor" pattern as the primary way in which
|
|
they apply functionality. The most common use of this pattern
|
|
is statement compilation, where individual expression classes match
|
|
up to rendering methods that produce a string result. Beyond this,
|
|
the visitor system is also used to inspect expressions for various
|
|
information and patterns, as well as for the purposes of applying
|
|
transformations to expressions.
|
|
|
|
Examples of how the visit system is used can be seen in the source code
|
|
of for example the ``sqlalchemy.sql.util`` and the ``sqlalchemy.sql.compiler``
|
|
modules. Some background on clause adaption is also at
|
|
https://techspot.zzzeek.org/2008/01/23/expression-transformations/ .
|
|
|
|
"""
|
|
|
|
from collections import deque
|
|
import itertools
|
|
import operator
|
|
|
|
from .. import exc
|
|
from .. import util
|
|
from ..util import langhelpers
|
|
from ..util import symbol
|
|
|
|
__all__ = [
|
|
"iterate",
|
|
"traverse_using",
|
|
"traverse",
|
|
"cloned_traverse",
|
|
"replacement_traverse",
|
|
"Traversible",
|
|
"TraversibleType",
|
|
"ExternalTraversal",
|
|
"InternalTraversal",
|
|
]
|
|
|
|
|
|
def _generate_compiler_dispatch(cls):
|
|
"""Generate a _compiler_dispatch() external traversal on classes with a
|
|
__visit_name__ attribute.
|
|
|
|
"""
|
|
visit_name = cls.__visit_name__
|
|
|
|
if "_compiler_dispatch" in cls.__dict__:
|
|
# class has a fixed _compiler_dispatch() method.
|
|
# copy it to "original" so that we can get it back if
|
|
# sqlalchemy.ext.compiles overrides it.
|
|
cls._original_compiler_dispatch = cls._compiler_dispatch
|
|
return
|
|
|
|
if not isinstance(visit_name, util.compat.string_types):
|
|
raise exc.InvalidRequestError(
|
|
"__visit_name__ on class %s must be a string at the class level"
|
|
% cls.__name__
|
|
)
|
|
|
|
name = "visit_%s" % visit_name
|
|
getter = operator.attrgetter(name)
|
|
|
|
def _compiler_dispatch(self, visitor, **kw):
|
|
"""Look for an attribute named "visit_<visit_name>" on the
|
|
visitor, and call it with the same kw params.
|
|
|
|
"""
|
|
try:
|
|
meth = getter(visitor)
|
|
except AttributeError as err:
|
|
return visitor.visit_unsupported_compilation(self, err, **kw)
|
|
|
|
else:
|
|
return meth(self, **kw)
|
|
|
|
cls._compiler_dispatch = (
|
|
cls._original_compiler_dispatch
|
|
) = _compiler_dispatch
|
|
|
|
|
|
class TraversibleType(type):
|
|
"""Metaclass which assigns dispatch attributes to various kinds of
|
|
"visitable" classes.
|
|
|
|
Attributes include:
|
|
|
|
* The ``_compiler_dispatch`` method, corresponding to ``__visit_name__``.
|
|
This is called "external traversal" because the caller of each visit()
|
|
method is responsible for sub-traversing the inner elements of each
|
|
object. This is appropriate for string compilers and other traversals
|
|
that need to call upon the inner elements in a specific pattern.
|
|
|
|
* internal traversal collections ``_children_traversal``,
|
|
``_cache_key_traversal``, ``_copy_internals_traversal``, generated from
|
|
an optional ``_traverse_internals`` collection of symbols which comes
|
|
from the :class:`.InternalTraversal` list of symbols. This is called
|
|
"internal traversal" MARKMARK
|
|
|
|
"""
|
|
|
|
def __init__(cls, clsname, bases, clsdict):
|
|
if clsname != "Traversible":
|
|
if "__visit_name__" in clsdict:
|
|
_generate_compiler_dispatch(cls)
|
|
|
|
super(TraversibleType, cls).__init__(clsname, bases, clsdict)
|
|
|
|
|
|
class Traversible(util.with_metaclass(TraversibleType)):
|
|
"""Base class for visitable objects, applies the
|
|
:class:`.visitors.TraversibleType` metaclass.
|
|
|
|
"""
|
|
|
|
def __class_getitem__(cls, key):
|
|
# allow generic classes in py3.9+
|
|
return cls
|
|
|
|
@util.preload_module("sqlalchemy.sql.traversals")
|
|
def get_children(self, omit_attrs=(), **kw):
|
|
r"""Return immediate child :class:`.visitors.Traversible`
|
|
elements of this :class:`.visitors.Traversible`.
|
|
|
|
This is used for visit traversal.
|
|
|
|
\**kw may contain flags that change the collection that is
|
|
returned, for example to return a subset of items in order to
|
|
cut down on larger traversals, or to return child items from a
|
|
different context (such as schema-level collections instead of
|
|
clause-level).
|
|
|
|
"""
|
|
|
|
traversals = util.preloaded.sql_traversals
|
|
|
|
try:
|
|
traverse_internals = self._traverse_internals
|
|
except AttributeError:
|
|
# user-defined classes may not have a _traverse_internals
|
|
return []
|
|
|
|
dispatch = traversals._get_children.run_generated_dispatch
|
|
return itertools.chain.from_iterable(
|
|
meth(obj, **kw)
|
|
for attrname, obj, meth in dispatch(
|
|
self, traverse_internals, "_generated_get_children_traversal"
|
|
)
|
|
if attrname not in omit_attrs and obj is not None
|
|
)
|
|
|
|
|
|
class _InternalTraversalType(type):
|
|
def __init__(cls, clsname, bases, clsdict):
|
|
if cls.__name__ in ("InternalTraversal", "ExtendedInternalTraversal"):
|
|
lookup = {}
|
|
for key, sym in clsdict.items():
|
|
if key.startswith("dp_"):
|
|
visit_key = key.replace("dp_", "visit_")
|
|
sym_name = sym.name
|
|
assert sym_name not in lookup, sym_name
|
|
lookup[sym] = lookup[sym_name] = visit_key
|
|
if hasattr(cls, "_dispatch_lookup"):
|
|
lookup.update(cls._dispatch_lookup)
|
|
cls._dispatch_lookup = lookup
|
|
|
|
super(_InternalTraversalType, cls).__init__(clsname, bases, clsdict)
|
|
|
|
|
|
def _generate_dispatcher(visitor, internal_dispatch, method_name):
|
|
names = []
|
|
for attrname, visit_sym in internal_dispatch:
|
|
meth = visitor.dispatch(visit_sym)
|
|
if meth:
|
|
visit_name = ExtendedInternalTraversal._dispatch_lookup[visit_sym]
|
|
names.append((attrname, visit_name))
|
|
|
|
code = (
|
|
(" return [\n")
|
|
+ (
|
|
", \n".join(
|
|
" (%r, self.%s, visitor.%s)"
|
|
% (attrname, attrname, visit_name)
|
|
for attrname, visit_name in names
|
|
)
|
|
)
|
|
+ ("\n ]\n")
|
|
)
|
|
meth_text = ("def %s(self, visitor):\n" % method_name) + code + "\n"
|
|
# print(meth_text)
|
|
return langhelpers._exec_code_in_env(meth_text, {}, method_name)
|
|
|
|
|
|
class InternalTraversal(util.with_metaclass(_InternalTraversalType, object)):
|
|
r"""Defines visitor symbols used for internal traversal.
|
|
|
|
The :class:`.InternalTraversal` class is used in two ways. One is that
|
|
it can serve as the superclass for an object that implements the
|
|
various visit methods of the class. The other is that the symbols
|
|
themselves of :class:`.InternalTraversal` are used within
|
|
the ``_traverse_internals`` collection. Such as, the :class:`.Case`
|
|
object defines ``_traverse_internals`` as ::
|
|
|
|
_traverse_internals = [
|
|
("value", InternalTraversal.dp_clauseelement),
|
|
("whens", InternalTraversal.dp_clauseelement_tuples),
|
|
("else_", InternalTraversal.dp_clauseelement),
|
|
]
|
|
|
|
Above, the :class:`.Case` class indicates its internal state as the
|
|
attributes named ``value``, ``whens``, and ``else_``. They each
|
|
link to an :class:`.InternalTraversal` method which indicates the type
|
|
of datastructure referred towards.
|
|
|
|
Using the ``_traverse_internals`` structure, objects of type
|
|
:class:`.InternalTraversible` will have the following methods automatically
|
|
implemented:
|
|
|
|
* :meth:`.Traversible.get_children`
|
|
|
|
* :meth:`.Traversible._copy_internals`
|
|
|
|
* :meth:`.Traversible._gen_cache_key`
|
|
|
|
Subclasses can also implement these methods directly, particularly for the
|
|
:meth:`.Traversible._copy_internals` method, when special steps
|
|
are needed.
|
|
|
|
.. versionadded:: 1.4
|
|
|
|
"""
|
|
|
|
def dispatch(self, visit_symbol):
|
|
"""Given a method from :class:`.InternalTraversal`, return the
|
|
corresponding method on a subclass.
|
|
|
|
"""
|
|
name = self._dispatch_lookup[visit_symbol]
|
|
return getattr(self, name, None)
|
|
|
|
def run_generated_dispatch(
|
|
self, target, internal_dispatch, generate_dispatcher_name
|
|
):
|
|
try:
|
|
dispatcher = target.__class__.__dict__[generate_dispatcher_name]
|
|
except KeyError:
|
|
# most of the dispatchers are generated up front
|
|
# in sqlalchemy/sql/__init__.py ->
|
|
# traversals.py-> _preconfigure_traversals().
|
|
# this block will generate any remaining dispatchers.
|
|
dispatcher = self.generate_dispatch(
|
|
target.__class__, internal_dispatch, generate_dispatcher_name
|
|
)
|
|
return dispatcher(target, self)
|
|
|
|
def generate_dispatch(
|
|
self, target_cls, internal_dispatch, generate_dispatcher_name
|
|
):
|
|
dispatcher = _generate_dispatcher(
|
|
self, internal_dispatch, generate_dispatcher_name
|
|
)
|
|
# assert isinstance(target_cls, type)
|
|
setattr(target_cls, generate_dispatcher_name, dispatcher)
|
|
return dispatcher
|
|
|
|
dp_has_cache_key = symbol("HC")
|
|
"""Visit a :class:`.HasCacheKey` object."""
|
|
|
|
dp_has_cache_key_list = symbol("HL")
|
|
"""Visit a list of :class:`.HasCacheKey` objects."""
|
|
|
|
dp_clauseelement = symbol("CE")
|
|
"""Visit a :class:`_expression.ClauseElement` object."""
|
|
|
|
dp_fromclause_canonical_column_collection = symbol("FC")
|
|
"""Visit a :class:`_expression.FromClause` object in the context of the
|
|
``columns`` attribute.
|
|
|
|
The column collection is "canonical", meaning it is the originally
|
|
defined location of the :class:`.ColumnClause` objects. Right now
|
|
this means that the object being visited is a
|
|
:class:`_expression.TableClause`
|
|
or :class:`_schema.Table` object only.
|
|
|
|
"""
|
|
|
|
dp_clauseelement_tuples = symbol("CTS")
|
|
"""Visit a list of tuples which contain :class:`_expression.ClauseElement`
|
|
objects.
|
|
|
|
"""
|
|
|
|
dp_clauseelement_list = symbol("CL")
|
|
"""Visit a list of :class:`_expression.ClauseElement` objects.
|
|
|
|
"""
|
|
|
|
dp_clauseelement_tuple = symbol("CT")
|
|
"""Visit a tuple of :class:`_expression.ClauseElement` objects.
|
|
|
|
"""
|
|
|
|
dp_executable_options = symbol("EO")
|
|
|
|
dp_with_context_options = symbol("WC")
|
|
|
|
dp_fromclause_ordered_set = symbol("CO")
|
|
"""Visit an ordered set of :class:`_expression.FromClause` objects. """
|
|
|
|
dp_string = symbol("S")
|
|
"""Visit a plain string value.
|
|
|
|
Examples include table and column names, bound parameter keys, special
|
|
keywords such as "UNION", "UNION ALL".
|
|
|
|
The string value is considered to be significant for cache key
|
|
generation.
|
|
|
|
"""
|
|
|
|
dp_string_list = symbol("SL")
|
|
"""Visit a list of strings."""
|
|
|
|
dp_anon_name = symbol("AN")
|
|
"""Visit a potentially "anonymized" string value.
|
|
|
|
The string value is considered to be significant for cache key
|
|
generation.
|
|
|
|
"""
|
|
|
|
dp_boolean = symbol("B")
|
|
"""Visit a boolean value.
|
|
|
|
The boolean value is considered to be significant for cache key
|
|
generation.
|
|
|
|
"""
|
|
|
|
dp_operator = symbol("O")
|
|
"""Visit an operator.
|
|
|
|
The operator is a function from the :mod:`sqlalchemy.sql.operators`
|
|
module.
|
|
|
|
The operator value is considered to be significant for cache key
|
|
generation.
|
|
|
|
"""
|
|
|
|
dp_type = symbol("T")
|
|
"""Visit a :class:`.TypeEngine` object
|
|
|
|
The type object is considered to be significant for cache key
|
|
generation.
|
|
|
|
"""
|
|
|
|
dp_plain_dict = symbol("PD")
|
|
"""Visit a dictionary with string keys.
|
|
|
|
The keys of the dictionary should be strings, the values should
|
|
be immutable and hashable. The dictionary is considered to be
|
|
significant for cache key generation.
|
|
|
|
"""
|
|
|
|
dp_dialect_options = symbol("DO")
|
|
"""Visit a dialect options structure."""
|
|
|
|
dp_string_clauseelement_dict = symbol("CD")
|
|
"""Visit a dictionary of string keys to :class:`_expression.ClauseElement`
|
|
objects.
|
|
|
|
"""
|
|
|
|
dp_string_multi_dict = symbol("MD")
|
|
"""Visit a dictionary of string keys to values which may either be
|
|
plain immutable/hashable or :class:`.HasCacheKey` objects.
|
|
|
|
"""
|
|
|
|
dp_annotations_key = symbol("AK")
|
|
"""Visit the _annotations_cache_key element.
|
|
|
|
This is a dictionary of additional information about a ClauseElement
|
|
that modifies its role. It should be included when comparing or caching
|
|
objects, however generating this key is relatively expensive. Visitors
|
|
should check the "_annotations" dict for non-None first before creating
|
|
this key.
|
|
|
|
"""
|
|
|
|
dp_plain_obj = symbol("PO")
|
|
"""Visit a plain python object.
|
|
|
|
The value should be immutable and hashable, such as an integer.
|
|
The value is considered to be significant for cache key generation.
|
|
|
|
"""
|
|
|
|
dp_named_ddl_element = symbol("DD")
|
|
"""Visit a simple named DDL element.
|
|
|
|
The current object used by this method is the :class:`.Sequence`.
|
|
|
|
The object is only considered to be important for cache key generation
|
|
as far as its name, but not any other aspects of it.
|
|
|
|
"""
|
|
|
|
dp_prefix_sequence = symbol("PS")
|
|
"""Visit the sequence represented by :class:`_expression.HasPrefixes`
|
|
or :class:`_expression.HasSuffixes`.
|
|
|
|
"""
|
|
|
|
dp_table_hint_list = symbol("TH")
|
|
"""Visit the ``_hints`` collection of a :class:`_expression.Select`
|
|
object.
|
|
|
|
"""
|
|
|
|
dp_setup_join_tuple = symbol("SJ")
|
|
|
|
dp_memoized_select_entities = symbol("ME")
|
|
|
|
dp_statement_hint_list = symbol("SH")
|
|
"""Visit the ``_statement_hints`` collection of a
|
|
:class:`_expression.Select`
|
|
object.
|
|
|
|
"""
|
|
|
|
dp_unknown_structure = symbol("UK")
|
|
"""Visit an unknown structure.
|
|
|
|
"""
|
|
|
|
dp_dml_ordered_values = symbol("DML_OV")
|
|
"""Visit the values() ordered tuple list of an
|
|
:class:`_expression.Update` object."""
|
|
|
|
dp_dml_values = symbol("DML_V")
|
|
"""Visit the values() dictionary of a :class:`.ValuesBase`
|
|
(e.g. Insert or Update) object.
|
|
|
|
"""
|
|
|
|
dp_dml_multi_values = symbol("DML_MV")
|
|
"""Visit the values() multi-valued list of dictionaries of an
|
|
:class:`_expression.Insert` object.
|
|
|
|
"""
|
|
|
|
dp_propagate_attrs = symbol("PA")
|
|
"""Visit the propagate attrs dict. This hardcodes to the particular
|
|
elements we care about right now."""
|
|
|
|
|
|
class ExtendedInternalTraversal(InternalTraversal):
|
|
"""Defines additional symbols that are useful in caching applications.
|
|
|
|
Traversals for :class:`_expression.ClauseElement` objects only need to use
|
|
those symbols present in :class:`.InternalTraversal`. However, for
|
|
additional caching use cases within the ORM, symbols dealing with the
|
|
:class:`.HasCacheKey` class are added here.
|
|
|
|
"""
|
|
|
|
dp_ignore = symbol("IG")
|
|
"""Specify an object that should be ignored entirely.
|
|
|
|
This currently applies function call argument caching where some
|
|
arguments should not be considered to be part of a cache key.
|
|
|
|
"""
|
|
|
|
dp_inspectable = symbol("IS")
|
|
"""Visit an inspectable object where the return value is a
|
|
:class:`.HasCacheKey` object."""
|
|
|
|
dp_multi = symbol("M")
|
|
"""Visit an object that may be a :class:`.HasCacheKey` or may be a
|
|
plain hashable object."""
|
|
|
|
dp_multi_list = symbol("MT")
|
|
"""Visit a tuple containing elements that may be :class:`.HasCacheKey` or
|
|
may be a plain hashable object."""
|
|
|
|
dp_has_cache_key_tuples = symbol("HT")
|
|
"""Visit a list of tuples which contain :class:`.HasCacheKey`
|
|
objects.
|
|
|
|
"""
|
|
|
|
dp_inspectable_list = symbol("IL")
|
|
"""Visit a list of inspectable objects which upon inspection are
|
|
HasCacheKey objects."""
|
|
|
|
|
|
class ExternalTraversal(object):
|
|
"""Base class for visitor objects which can traverse externally using
|
|
the :func:`.visitors.traverse` function.
|
|
|
|
Direct usage of the :func:`.visitors.traverse` function is usually
|
|
preferred.
|
|
|
|
"""
|
|
|
|
__traverse_options__ = {}
|
|
|
|
def traverse_single(self, obj, **kw):
|
|
for v in self.visitor_iterator:
|
|
meth = getattr(v, "visit_%s" % obj.__visit_name__, None)
|
|
if meth:
|
|
return meth(obj, **kw)
|
|
|
|
def iterate(self, obj):
|
|
"""Traverse the given expression structure, returning an iterator
|
|
of all elements.
|
|
|
|
"""
|
|
return iterate(obj, self.__traverse_options__)
|
|
|
|
def traverse(self, obj):
|
|
"""Traverse and visit the given expression structure."""
|
|
|
|
return traverse(obj, self.__traverse_options__, self._visitor_dict)
|
|
|
|
@util.memoized_property
|
|
def _visitor_dict(self):
|
|
visitors = {}
|
|
|
|
for name in dir(self):
|
|
if name.startswith("visit_"):
|
|
visitors[name[6:]] = getattr(self, name)
|
|
return visitors
|
|
|
|
@property
|
|
def visitor_iterator(self):
|
|
"""Iterate through this visitor and each 'chained' visitor."""
|
|
|
|
v = self
|
|
while v:
|
|
yield v
|
|
v = getattr(v, "_next", None)
|
|
|
|
def chain(self, visitor):
|
|
"""'Chain' an additional ClauseVisitor onto this ClauseVisitor.
|
|
|
|
The chained visitor will receive all visit events after this one.
|
|
|
|
"""
|
|
tail = list(self.visitor_iterator)[-1]
|
|
tail._next = visitor
|
|
return self
|
|
|
|
|
|
class CloningExternalTraversal(ExternalTraversal):
|
|
"""Base class for visitor objects which can traverse using
|
|
the :func:`.visitors.cloned_traverse` function.
|
|
|
|
Direct usage of the :func:`.visitors.cloned_traverse` function is usually
|
|
preferred.
|
|
|
|
|
|
"""
|
|
|
|
def copy_and_process(self, list_):
|
|
"""Apply cloned traversal to the given list of elements, and return
|
|
the new list.
|
|
|
|
"""
|
|
return [self.traverse(x) for x in list_]
|
|
|
|
def traverse(self, obj):
|
|
"""Traverse and visit the given expression structure."""
|
|
|
|
return cloned_traverse(
|
|
obj, self.__traverse_options__, self._visitor_dict
|
|
)
|
|
|
|
|
|
class ReplacingExternalTraversal(CloningExternalTraversal):
|
|
"""Base class for visitor objects which can traverse using
|
|
the :func:`.visitors.replacement_traverse` function.
|
|
|
|
Direct usage of the :func:`.visitors.replacement_traverse` function is
|
|
usually preferred.
|
|
|
|
"""
|
|
|
|
def replace(self, elem):
|
|
"""Receive pre-copied elements during a cloning traversal.
|
|
|
|
If the method returns a new element, the element is used
|
|
instead of creating a simple copy of the element. Traversal
|
|
will halt on the newly returned element if it is re-encountered.
|
|
"""
|
|
return None
|
|
|
|
def traverse(self, obj):
|
|
"""Traverse and visit the given expression structure."""
|
|
|
|
def replace(elem):
|
|
for v in self.visitor_iterator:
|
|
e = v.replace(elem)
|
|
if e is not None:
|
|
return e
|
|
|
|
return replacement_traverse(obj, self.__traverse_options__, replace)
|
|
|
|
|
|
# backwards compatibility
|
|
Visitable = Traversible
|
|
VisitableType = TraversibleType
|
|
ClauseVisitor = ExternalTraversal
|
|
CloningVisitor = CloningExternalTraversal
|
|
ReplacingCloningVisitor = ReplacingExternalTraversal
|
|
|
|
|
|
def iterate(obj, opts=util.immutabledict()):
|
|
r"""Traverse the given expression structure, returning an iterator.
|
|
|
|
Traversal is configured to be breadth-first.
|
|
|
|
The central API feature used by the :func:`.visitors.iterate`
|
|
function is the
|
|
:meth:`_expression.ClauseElement.get_children` method of
|
|
:class:`_expression.ClauseElement` objects. This method should return all
|
|
the :class:`_expression.ClauseElement` objects which are associated with a
|
|
particular :class:`_expression.ClauseElement` object. For example, a
|
|
:class:`.Case` structure will refer to a series of
|
|
:class:`_expression.ColumnElement` objects within its "whens" and "else\_"
|
|
member variables.
|
|
|
|
:param obj: :class:`_expression.ClauseElement` structure to be traversed
|
|
|
|
:param opts: dictionary of iteration options. This dictionary is usually
|
|
empty in modern usage.
|
|
|
|
"""
|
|
yield obj
|
|
children = obj.get_children(**opts)
|
|
|
|
if not children:
|
|
return
|
|
|
|
stack = deque([children])
|
|
while stack:
|
|
t_iterator = stack.popleft()
|
|
for t in t_iterator:
|
|
yield t
|
|
stack.append(t.get_children(**opts))
|
|
|
|
|
|
def traverse_using(iterator, obj, visitors):
|
|
"""Visit the given expression structure using the given iterator of
|
|
objects.
|
|
|
|
:func:`.visitors.traverse_using` is usually called internally as the result
|
|
of the :func:`.visitors.traverse` function.
|
|
|
|
:param iterator: an iterable or sequence which will yield
|
|
:class:`_expression.ClauseElement`
|
|
structures; the iterator is assumed to be the
|
|
product of the :func:`.visitors.iterate` function.
|
|
|
|
:param obj: the :class:`_expression.ClauseElement`
|
|
that was used as the target of the
|
|
:func:`.iterate` function.
|
|
|
|
:param visitors: dictionary of visit functions. See :func:`.traverse`
|
|
for details on this dictionary.
|
|
|
|
.. seealso::
|
|
|
|
:func:`.traverse`
|
|
|
|
|
|
"""
|
|
for target in iterator:
|
|
meth = visitors.get(target.__visit_name__, None)
|
|
if meth:
|
|
meth(target)
|
|
return obj
|
|
|
|
|
|
def traverse(obj, opts, visitors):
|
|
"""Traverse and visit the given expression structure using the default
|
|
iterator.
|
|
|
|
e.g.::
|
|
|
|
from sqlalchemy.sql import visitors
|
|
|
|
stmt = select(some_table).where(some_table.c.foo == 'bar')
|
|
|
|
def visit_bindparam(bind_param):
|
|
print("found bound value: %s" % bind_param.value)
|
|
|
|
visitors.traverse(stmt, {}, {"bindparam": visit_bindparam})
|
|
|
|
The iteration of objects uses the :func:`.visitors.iterate` function,
|
|
which does a breadth-first traversal using a stack.
|
|
|
|
:param obj: :class:`_expression.ClauseElement` structure to be traversed
|
|
|
|
:param opts: dictionary of iteration options. This dictionary is usually
|
|
empty in modern usage.
|
|
|
|
:param visitors: dictionary of visit functions. The dictionary should
|
|
have strings as keys, each of which would correspond to the
|
|
``__visit_name__`` of a particular kind of SQL expression object, and
|
|
callable functions as values, each of which represents a visitor function
|
|
for that kind of object.
|
|
|
|
"""
|
|
return traverse_using(iterate(obj, opts), obj, visitors)
|
|
|
|
|
|
def cloned_traverse(obj, opts, visitors):
|
|
"""Clone the given expression structure, allowing modifications by
|
|
visitors.
|
|
|
|
Traversal usage is the same as that of :func:`.visitors.traverse`.
|
|
The visitor functions present in the ``visitors`` dictionary may also
|
|
modify the internals of the given structure as the traversal proceeds.
|
|
|
|
The central API feature used by the :func:`.visitors.cloned_traverse`
|
|
and :func:`.visitors.replacement_traverse` functions, in addition to the
|
|
:meth:`_expression.ClauseElement.get_children`
|
|
function that is used to achieve
|
|
the iteration, is the :meth:`_expression.ClauseElement._copy_internals`
|
|
method.
|
|
For a :class:`_expression.ClauseElement`
|
|
structure to support cloning and replacement
|
|
traversals correctly, it needs to be able to pass a cloning function into
|
|
its internal members in order to make copies of them.
|
|
|
|
.. seealso::
|
|
|
|
:func:`.visitors.traverse`
|
|
|
|
:func:`.visitors.replacement_traverse`
|
|
|
|
"""
|
|
|
|
cloned = {}
|
|
stop_on = set(opts.get("stop_on", []))
|
|
|
|
def deferred_copy_internals(obj):
|
|
return cloned_traverse(obj, opts, visitors)
|
|
|
|
def clone(elem, **kw):
|
|
if elem in stop_on:
|
|
return elem
|
|
else:
|
|
if id(elem) not in cloned:
|
|
|
|
if "replace" in kw:
|
|
newelem = kw["replace"](elem)
|
|
if newelem is not None:
|
|
cloned[id(elem)] = newelem
|
|
return newelem
|
|
|
|
cloned[id(elem)] = newelem = elem._clone(clone=clone, **kw)
|
|
newelem._copy_internals(clone=clone, **kw)
|
|
meth = visitors.get(newelem.__visit_name__, None)
|
|
if meth:
|
|
meth(newelem)
|
|
return cloned[id(elem)]
|
|
|
|
if obj is not None:
|
|
obj = clone(
|
|
obj, deferred_copy_internals=deferred_copy_internals, **opts
|
|
)
|
|
clone = None # remove gc cycles
|
|
return obj
|
|
|
|
|
|
def replacement_traverse(obj, opts, replace):
|
|
"""Clone the given expression structure, allowing element
|
|
replacement by a given replacement function.
|
|
|
|
This function is very similar to the :func:`.visitors.cloned_traverse`
|
|
function, except instead of being passed a dictionary of visitors, all
|
|
elements are unconditionally passed into the given replace function.
|
|
The replace function then has the option to return an entirely new object
|
|
which will replace the one given. If it returns ``None``, then the object
|
|
is kept in place.
|
|
|
|
The difference in usage between :func:`.visitors.cloned_traverse` and
|
|
:func:`.visitors.replacement_traverse` is that in the former case, an
|
|
already-cloned object is passed to the visitor function, and the visitor
|
|
function can then manipulate the internal state of the object.
|
|
In the case of the latter, the visitor function should only return an
|
|
entirely different object, or do nothing.
|
|
|
|
The use case for :func:`.visitors.replacement_traverse` is that of
|
|
replacing a FROM clause inside of a SQL structure with a different one,
|
|
as is a common use case within the ORM.
|
|
|
|
"""
|
|
|
|
cloned = {}
|
|
stop_on = {id(x) for x in opts.get("stop_on", [])}
|
|
|
|
def deferred_copy_internals(obj):
|
|
return replacement_traverse(obj, opts, replace)
|
|
|
|
def clone(elem, **kw):
|
|
if (
|
|
id(elem) in stop_on
|
|
or "no_replacement_traverse" in elem._annotations
|
|
):
|
|
return elem
|
|
else:
|
|
newelem = replace(elem)
|
|
if newelem is not None:
|
|
stop_on.add(id(newelem))
|
|
return newelem
|
|
else:
|
|
# base "already seen" on id(), not hash, so that we don't
|
|
# replace an Annotated element with its non-annotated one, and
|
|
# vice versa
|
|
id_elem = id(elem)
|
|
if id_elem not in cloned:
|
|
if "replace" in kw:
|
|
newelem = kw["replace"](elem)
|
|
if newelem is not None:
|
|
cloned[id_elem] = newelem
|
|
return newelem
|
|
|
|
cloned[id_elem] = newelem = elem._clone(**kw)
|
|
newelem._copy_internals(clone=clone, **kw)
|
|
return cloned[id_elem]
|
|
|
|
if obj is not None:
|
|
obj = clone(
|
|
obj, deferred_copy_internals=deferred_copy_internals, **opts
|
|
)
|
|
clone = None # remove gc cycles
|
|
return obj
|