Edit File: rewriter.py
from __future__ import annotations from typing import Any from typing import Callable from typing import Iterator from typing import List from typing import Optional from typing import Type from typing import TYPE_CHECKING from typing import Union from alembic import util from alembic.operations import ops if TYPE_CHECKING: from alembic.operations.ops import AddColumnOp from alembic.operations.ops import AlterColumnOp from alembic.operations.ops import CreateTableOp from alembic.operations.ops import MigrateOperation from alembic.operations.ops import MigrationScript from alembic.operations.ops import ModifyTableOps from alembic.operations.ops import OpContainer from alembic.runtime.migration import MigrationContext from alembic.script.revision import Revision 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: Optional[Rewriter] = None def __init__(self) -> None: self.dispatch = util.Dispatcher() def chain(self, other: Rewriter) -> Rewriter: """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: Union[ Type[AddColumnOp], Type[MigrateOperation], Type[AlterColumnOp], Type[CreateTableOp], Type[ModifyTableOps], ], ) -> Callable: """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: Revision, 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: Revision, directives: List[MigrationScript], ) -> None: 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: MigrationContext, revision: Revision, directive: MigrationScript, ) -> None: upgrade_ops_list = [] 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 downgrade_ops_list = [] 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 @_traverse.dispatch_for(ops.OpContainer) def _traverse_op_container( self, context: MigrationContext, revision: Revision, directive: OpContainer, ) -> None: self._traverse_list(context, revision, directive.ops) @_traverse.dispatch_for(ops.MigrateOperation) def _traverse_any_directive( self, context: MigrationContext, revision: Revision, directive: MigrateOperation, ) -> None: pass def _traverse_for( self, context: MigrationContext, revision: Revision, 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: Revision, 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: Revision, directives: List[MigrationScript], ) -> None: self._traverse_list(context, revision, directives)