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