445 lines
16 KiB
Python
445 lines
16 KiB
Python
from contextlib import contextmanager
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from .. import util
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from ..util import sqla_compat
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from . import batch
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from . import schemaobj
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from ..util.compat import exec_
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import textwrap
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import inspect
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__all__ = ('Operations', 'BatchOperations')
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try:
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from sqlalchemy.sql.naming import conv
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except:
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conv = None
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class Operations(util.ModuleClsProxy):
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"""Define high level migration operations.
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Each operation corresponds to some schema migration operation,
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executed against a particular :class:`.MigrationContext`
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which in turn represents connectivity to a database,
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or a file output stream.
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While :class:`.Operations` is normally configured as
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part of the :meth:`.EnvironmentContext.run_migrations`
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method called from an ``env.py`` script, a standalone
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:class:`.Operations` instance can be
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made for use cases external to regular Alembic
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migrations by passing in a :class:`.MigrationContext`::
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from alembic.migration import MigrationContext
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from alembic.operations import Operations
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conn = myengine.connect()
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ctx = MigrationContext.configure(conn)
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op = Operations(ctx)
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op.alter_column("t", "c", nullable=True)
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Note that as of 0.8, most of the methods on this class are produced
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dynamically using the :meth:`.Operations.register_operation`
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method.
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"""
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_to_impl = util.Dispatcher()
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def __init__(self, migration_context, impl=None):
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"""Construct a new :class:`.Operations`
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:param migration_context: a :class:`.MigrationContext`
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instance.
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"""
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self.migration_context = migration_context
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if impl is None:
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self.impl = migration_context.impl
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else:
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self.impl = impl
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self.schema_obj = schemaobj.SchemaObjects(migration_context)
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@classmethod
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def register_operation(cls, name, sourcename=None):
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"""Register a new operation for this class.
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This method is normally used to add new operations
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to the :class:`.Operations` class, and possibly the
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:class:`.BatchOperations` class as well. All Alembic migration
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operations are implemented via this system, however the system
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is also available as a public API to facilitate adding custom
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operations.
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.. versionadded:: 0.8.0
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.. seealso::
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:ref:`operation_plugins`
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"""
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def register(op_cls):
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if sourcename is None:
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fn = getattr(op_cls, name)
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source_name = fn.__name__
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else:
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fn = getattr(op_cls, sourcename)
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source_name = fn.__name__
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spec = inspect.getargspec(fn)
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name_args = spec[0]
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assert name_args[0:2] == ['cls', 'operations']
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name_args[0:2] = ['self']
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args = inspect.formatargspec(*spec)
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num_defaults = len(spec[3]) if spec[3] else 0
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if num_defaults:
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defaulted_vals = name_args[0 - num_defaults:]
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else:
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defaulted_vals = ()
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apply_kw = inspect.formatargspec(
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name_args, spec[1], spec[2],
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defaulted_vals,
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formatvalue=lambda x: '=' + x)
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func_text = textwrap.dedent("""\
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def %(name)s%(args)s:
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%(doc)r
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return op_cls.%(source_name)s%(apply_kw)s
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""" % {
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'name': name,
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'source_name': source_name,
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'args': args,
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'apply_kw': apply_kw,
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'doc': fn.__doc__,
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'meth': fn.__name__
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})
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globals_ = {'op_cls': op_cls}
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lcl = {}
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exec_(func_text, globals_, lcl)
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setattr(cls, name, lcl[name])
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fn.__func__.__doc__ = "This method is proxied on "\
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"the :class:`.%s` class, via the :meth:`.%s.%s` method." % (
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cls.__name__, cls.__name__, name
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)
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if hasattr(fn, '_legacy_translations'):
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lcl[name]._legacy_translations = fn._legacy_translations
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return op_cls
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return register
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@classmethod
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def implementation_for(cls, op_cls):
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"""Register an implementation for a given :class:`.MigrateOperation`.
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This is part of the operation extensibility API.
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.. seealso::
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:ref:`operation_plugins` - example of use
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"""
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def decorate(fn):
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cls._to_impl.dispatch_for(op_cls)(fn)
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return fn
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return decorate
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@classmethod
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@contextmanager
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def context(cls, migration_context):
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op = Operations(migration_context)
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op._install_proxy()
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yield op
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op._remove_proxy()
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@contextmanager
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def batch_alter_table(
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self, table_name, schema=None, recreate="auto", copy_from=None,
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table_args=(), table_kwargs=util.immutabledict(),
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reflect_args=(), reflect_kwargs=util.immutabledict(),
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naming_convention=None):
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"""Invoke a series of per-table migrations in batch.
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Batch mode allows a series of operations specific to a table
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to be syntactically grouped together, and allows for alternate
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modes of table migration, in particular the "recreate" style of
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migration required by SQLite.
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"recreate" style is as follows:
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1. A new table is created with the new specification, based on the
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migration directives within the batch, using a temporary name.
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2. the data copied from the existing table to the new table.
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3. the existing table is dropped.
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4. the new table is renamed to the existing table name.
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The directive by default will only use "recreate" style on the
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SQLite backend, and only if directives are present which require
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this form, e.g. anything other than ``add_column()``. The batch
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operation on other backends will proceed using standard ALTER TABLE
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operations.
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The method is used as a context manager, which returns an instance
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of :class:`.BatchOperations`; this object is the same as
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:class:`.Operations` except that table names and schema names
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are omitted. E.g.::
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with op.batch_alter_table("some_table") as batch_op:
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batch_op.add_column(Column('foo', Integer))
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batch_op.drop_column('bar')
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The operations within the context manager are invoked at once
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when the context is ended. When run against SQLite, if the
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migrations include operations not supported by SQLite's ALTER TABLE,
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the entire table will be copied to a new one with the new
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specification, moving all data across as well.
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The copy operation by default uses reflection to retrieve the current
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structure of the table, and therefore :meth:`.batch_alter_table`
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in this mode requires that the migration is run in "online" mode.
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The ``copy_from`` parameter may be passed which refers to an existing
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:class:`.Table` object, which will bypass this reflection step.
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.. note:: The table copy operation will currently not copy
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CHECK constraints, and may not copy UNIQUE constraints that are
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unnamed, as is possible on SQLite. See the section
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:ref:`sqlite_batch_constraints` for workarounds.
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:param table_name: name of table
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:param schema: optional schema name.
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:param recreate: under what circumstances the table should be
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recreated. At its default of ``"auto"``, the SQLite dialect will
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recreate the table if any operations other than ``add_column()``,
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``create_index()``, or ``drop_index()`` are
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present. Other options include ``"always"`` and ``"never"``.
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:param copy_from: optional :class:`~sqlalchemy.schema.Table` object
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that will act as the structure of the table being copied. If omitted,
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table reflection is used to retrieve the structure of the table.
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.. versionadded:: 0.7.6 Fully implemented the
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:paramref:`~.Operations.batch_alter_table.copy_from`
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parameter.
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.. seealso::
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:ref:`batch_offline_mode`
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:paramref:`~.Operations.batch_alter_table.reflect_args`
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:paramref:`~.Operations.batch_alter_table.reflect_kwargs`
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:param reflect_args: a sequence of additional positional arguments that
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will be applied to the table structure being reflected / copied;
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this may be used to pass column and constraint overrides to the
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table that will be reflected, in lieu of passing the whole
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:class:`~sqlalchemy.schema.Table` using
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:paramref:`~.Operations.batch_alter_table.copy_from`.
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.. versionadded:: 0.7.1
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:param reflect_kwargs: a dictionary of additional keyword arguments
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that will be applied to the table structure being copied; this may be
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used to pass additional table and reflection options to the table that
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will be reflected, in lieu of passing the whole
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:class:`~sqlalchemy.schema.Table` using
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:paramref:`~.Operations.batch_alter_table.copy_from`.
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.. versionadded:: 0.7.1
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:param table_args: a sequence of additional positional arguments that
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will be applied to the new :class:`~sqlalchemy.schema.Table` when
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created, in addition to those copied from the source table.
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This may be used to provide additional constraints such as CHECK
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constraints that may not be reflected.
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:param table_kwargs: a dictionary of additional keyword arguments
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that will be applied to the new :class:`~sqlalchemy.schema.Table`
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when created, in addition to those copied from the source table.
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This may be used to provide for additional table options that may
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not be reflected.
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.. versionadded:: 0.7.0
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:param naming_convention: a naming convention dictionary of the form
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described at :ref:`autogen_naming_conventions` which will be applied
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to the :class:`~sqlalchemy.schema.MetaData` during the reflection
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process. This is typically required if one wants to drop SQLite
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constraints, as these constraints will not have names when
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reflected on this backend. Requires SQLAlchemy **0.9.4** or greater.
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.. seealso::
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:ref:`dropping_sqlite_foreign_keys`
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.. versionadded:: 0.7.1
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.. note:: batch mode requires SQLAlchemy 0.8 or above.
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.. seealso::
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:ref:`batch_migrations`
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"""
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impl = batch.BatchOperationsImpl(
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self, table_name, schema, recreate,
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copy_from, table_args, table_kwargs, reflect_args,
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reflect_kwargs, naming_convention)
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batch_op = BatchOperations(self.migration_context, impl=impl)
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yield batch_op
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impl.flush()
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def get_context(self):
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"""Return the :class:`.MigrationContext` object that's
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currently in use.
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"""
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return self.migration_context
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def invoke(self, operation):
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"""Given a :class:`.MigrateOperation`, invoke it in terms of
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this :class:`.Operations` instance.
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.. versionadded:: 0.8.0
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"""
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fn = self._to_impl.dispatch(
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operation, self.migration_context.impl.__dialect__)
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return fn(self, operation)
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def f(self, name):
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"""Indicate a string name that has already had a naming convention
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applied to it.
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This feature combines with the SQLAlchemy ``naming_convention`` feature
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to disambiguate constraint names that have already had naming
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conventions applied to them, versus those that have not. This is
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necessary in the case that the ``"%(constraint_name)s"`` token
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is used within a naming convention, so that it can be identified
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that this particular name should remain fixed.
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If the :meth:`.Operations.f` is used on a constraint, the naming
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convention will not take effect::
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op.add_column('t', 'x', Boolean(name=op.f('ck_bool_t_x')))
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Above, the CHECK constraint generated will have the name
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``ck_bool_t_x`` regardless of whether or not a naming convention is
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in use.
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Alternatively, if a naming convention is in use, and 'f' is not used,
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names will be converted along conventions. If the ``target_metadata``
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contains the naming convention
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``{"ck": "ck_bool_%(table_name)s_%(constraint_name)s"}``, then the
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output of the following:
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op.add_column('t', 'x', Boolean(name='x'))
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will be::
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CONSTRAINT ck_bool_t_x CHECK (x in (1, 0)))
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The function is rendered in the output of autogenerate when
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a particular constraint name is already converted, for SQLAlchemy
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version **0.9.4 and greater only**. Even though ``naming_convention``
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was introduced in 0.9.2, the string disambiguation service is new
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as of 0.9.4.
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.. versionadded:: 0.6.4
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"""
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if conv:
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return conv(name)
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else:
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raise NotImplementedError(
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"op.f() feature requires SQLAlchemy 0.9.4 or greater.")
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def inline_literal(self, value, type_=None):
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"""Produce an 'inline literal' expression, suitable for
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using in an INSERT, UPDATE, or DELETE statement.
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When using Alembic in "offline" mode, CRUD operations
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aren't compatible with SQLAlchemy's default behavior surrounding
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literal values,
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which is that they are converted into bound values and passed
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separately into the ``execute()`` method of the DBAPI cursor.
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An offline SQL
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script needs to have these rendered inline. While it should
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always be noted that inline literal values are an **enormous**
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security hole in an application that handles untrusted input,
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a schema migration is not run in this context, so
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literals are safe to render inline, with the caveat that
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advanced types like dates may not be supported directly
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by SQLAlchemy.
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See :meth:`.execute` for an example usage of
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:meth:`.inline_literal`.
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The environment can also be configured to attempt to render
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"literal" values inline automatically, for those simple types
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that are supported by the dialect; see
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:paramref:`.EnvironmentContext.configure.literal_binds` for this
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more recently added feature.
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:param value: The value to render. Strings, integers, and simple
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numerics should be supported. Other types like boolean,
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dates, etc. may or may not be supported yet by various
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backends.
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:param type_: optional - a :class:`sqlalchemy.types.TypeEngine`
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subclass stating the type of this value. In SQLAlchemy
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expressions, this is usually derived automatically
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from the Python type of the value itself, as well as
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based on the context in which the value is used.
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.. seealso::
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:paramref:`.EnvironmentContext.configure.literal_binds`
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"""
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return sqla_compat._literal_bindparam(None, value, type_=type_)
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def get_bind(self):
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"""Return the current 'bind'.
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Under normal circumstances, this is the
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:class:`~sqlalchemy.engine.Connection` currently being used
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to emit SQL to the database.
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In a SQL script context, this value is ``None``. [TODO: verify this]
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"""
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return self.migration_context.impl.bind
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class BatchOperations(Operations):
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"""Modifies the interface :class:`.Operations` for batch mode.
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This basically omits the ``table_name`` and ``schema`` parameters
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from associated methods, as these are a given when running under batch
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mode.
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.. seealso::
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:meth:`.Operations.batch_alter_table`
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Note that as of 0.8, most of the methods on this class are produced
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dynamically using the :meth:`.Operations.register_operation`
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method.
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"""
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def _noop(self, operation):
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raise NotImplementedError(
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"The %s method does not apply to a batch table alter operation."
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% operation)
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