def __init__(self):
self.dispatch = util.Dispatcher()
class Rewriter(object):
"""A helper object that allows easy 'rewriting' of ops streams.
The :class:`.Rewriter` object is intended to be passed along
to the
:paramref:`.EnvironmentContext.configure.process_revision_directives`
parameter in an ``env.py`` script. Once constructed, any number
of "rewrites" functions can be associated with it, which will be given
the opportunity to modify the structure without having to have explicit
knowledge of the overall structure.
The function is passed the :class:`.MigrationContext` object and
``revision`` tuple that are passed to the :paramref:`.Environment
Context.configure.process_revision_directives` function normally,
and the third argument is an individual directive of the type
noted in the decorator. The function has the choice of returning
a single op directive, which normally can be the directive that
was actually passed, or a new directive to replace it, or a list
of zero or more directives to replace it.
.. seealso::
:ref:`autogen_rewriter` - usage example
.. versionadded:: 0.8
"""
_traverse = util.Dispatcher()
_chained = None
def __init__(self):
self.dispatch = util.Dispatcher()
def chain(self, other):
"""Produce a "chain" of this :class:`.Rewriter` to another.
This allows two rewriters to operate serially on a stream,
e.g.::
writer1 = autogenerate.Rewriter()
writer2 = autogenerate.Rewriter()
@writer1.rewrites(ops.AddColumnOp)
def add_column_nullable(context, revision, op):
op.column.nullable = True
return op
@writer2.rewrites(ops.AddColumnOp)
def add_column_idx(context, revision, op):
idx_op = ops.CreateIndexOp(
'ixc', op.table_name, [op.column.name])
return [
op,
idx_op
]
writer = writer1.chain(writer2)
:param other: a :class:`.Rewriter` instance
:return: a new :class:`.Rewriter` that will run the operations
of this writer, then the "other" writer, in succession.
"""
wr = self.__class__.__new__(self.__class__)
wr.__dict__.update(self.__dict__)
wr._chained = other
return wr
def rewrites(self, operator):
"""Register a function as rewriter for a given type.
The function should receive three arguments, which are
the :class:`.MigrationContext`, a ``revision`` tuple, and
an op directive of the type indicated. E.g.::
@writer1.rewrites(ops.AddColumnOp)
def add_column_nullable(context, revision, op):
op.column.nullable = True
return op
"""
return self.dispatch.dispatch_for(operator)
def _rewrite(self, context, revision, directive):
try:
_rewriter = self.dispatch.dispatch(directive)
except ValueError:
_rewriter = None
yield directive
else:
for r_directive in util.to_list(
_rewriter(context, revision, directive)):
yield r_directive
def __call__(self, context, revision, directives):
self.process_revision_directives(context, revision, directives)
if self._chained:
self._chained(context, revision, directives)
@_traverse.dispatch_for(ops.MigrationScript)
def _traverse_script(self, context, revision, directive):
upgrade_ops_list = []
for upgrade_ops in directive.upgrade_ops_list:
ret = self._traverse_for(context, revision, directive.upgrade_ops)
if len(ret) != 1:
raise ValueError(
"Can only return single object for UpgradeOps traverse")
upgrade_ops_list.append(ret[0])
directive.upgrade_ops = upgrade_ops_list
downgrade_ops_list = []
for downgrade_ops in directive.downgrade_ops_list:
ret = self._traverse_for(context, revision,
directive.downgrade_ops)
if len(ret) != 1:
raise ValueError(
"Can only return single object for DowngradeOps traverse")
downgrade_ops_list.append(ret[0])
directive.downgrade_ops = downgrade_ops_list
@_traverse.dispatch_for(ops.OpContainer)
def _traverse_op_container(self, context, revision, directive):
self._traverse_list(context, revision, directive.ops)
@_traverse.dispatch_for(ops.MigrateOperation)
def _traverse_any_directive(self, context, revision, directive):
pass
def _traverse_for(self, context, revision, directive):
directives = list(self._rewrite(context, revision, directive))
for directive in directives:
traverser = self._traverse.dispatch(directive)
traverser(self, context, revision, directive)
return directives
def _traverse_list(self, context, revision, directives):
dest = []
for directive in directives:
dest.extend(self._traverse_for(context, revision, directive))
directives[:] = dest
def process_revision_directives(self, context, revision, directives):
self._traverse_list(context, revision, directives)
def __init__(self) -> None:
self.dispatch = util.Dispatcher()