from __future__ import annotations
from typing import Any
from typing import Callable
from typing import Iterator
from typing import List
from typing import Tuple
from typing import Type
from typing import TYPE_CHECKING
from typing import Union
from .. import util
from ..operations import ops
if TYPE_CHECKING:
from ..operations.ops import AddColumnOp
from ..operations.ops import AlterColumnOp
from ..operations.ops import CreateTableOp
from ..operations.ops import DowngradeOps
from ..operations.ops import MigrateOperation
from ..operations.ops import MigrationScript
from ..operations.ops import ModifyTableOps
from ..operations.ops import OpContainer
from ..operations.ops import UpgradeOps
from ..runtime.migration import MigrationContext
from ..script.revision import _GetRevArg
ProcessRevisionDirectiveFn = Callable[
["MigrationContext", "_GetRevArg", List["MigrationScript"]], None
]
class Rewriter:
"""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
"""
_traverse = util.Dispatcher()
_chained: Tuple[Union[ProcessRevisionDirectiveFn, Rewriter], ...] = ()
def __init__(self) -> None:
self.dispatch = util.Dispatcher()
def chain(
self,
other: Union[
ProcessRevisionDirectiveFn,
Rewriter,
],
) -> Rewriter:
"""Produce a "chain" of this :class:`.Rewriter` to another.
This allows two or more 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: Union[
Type[AddColumnOp],
Type[MigrateOperation],
Type[AlterColumnOp],
Type[CreateTableOp],
Type[ModifyTableOps],
],
) -> Callable[..., Any]:
"""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: MigrationContext,
revision: _GetRevArg,
directive: MigrateOperation,
) -> Iterator[MigrateOperation]:
try:
_rewriter = self.dispatch.dispatch(directive)
except ValueError:
_rewriter = None
yield directive
else:
if self in directive._mutations:
yield directive
else:
for r_directive in util.to_list(
_rewriter(context, revision, directive), []
):
r_directive._mutations = r_directive._mutations.union(
[self]
)
yield r_directive
def __call__(
self,
context: MigrationContext,
revision: _GetRevArg,
directives: List[MigrationScript],
) -> None:
self.process_revision_directives(context, revision, directives)
for process_revision_directives in self._chained:
process_revision_directives(context, revision, directives)
@_traverse.dispatch_for(ops.MigrationScript)
def _traverse_script(
self,
context: MigrationContext,
revision: _GetRevArg,
directive: MigrationScript,
) -> None:
upgrade_ops_list: List[UpgradeOps] = []
for upgrade_ops in directive.upgrade_ops_list:
ret = self._traverse_for(context, revision, 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 # type: ignore
downgrade_ops_list: List[DowngradeOps] = []
for downgrade_ops in directive.downgrade_ops_list:
ret = self._traverse_for(context, revision, 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 # type: ignore
@_traverse.dispatch_for(ops.OpContainer)
def _traverse_op_container(
self,
context: MigrationContext,
revision: _GetRevArg,
directive: OpContainer,
) -> None:
self._traverse_list(context, revision, directive.ops)
@_traverse.dispatch_for(ops.MigrateOperation)
def _traverse_any_directive(
self,
context: MigrationContext,
revision: _GetRevArg,
directive: MigrateOperation,
) -> None:
pass
def _traverse_for(
self,
context: MigrationContext,
revision: _GetRevArg,
directive: MigrateOperation,
) -> Any:
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: MigrationContext,
revision: _GetRevArg,
directives: Any,
) -> None:
dest = []
for directive in directives:
dest.extend(self._traverse_for(context, revision, directive))
directives[:] = dest
def process_revision_directives(
self,
context: MigrationContext,
revision: _GetRevArg,
directives: List[MigrationScript],
) -> None:
self._traverse_list(context, revision, directives)
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