import io import logging import sys from contextlib import contextmanager from sqlalchemy import MetaData, Table, Column, String, literal_column from sqlalchemy import create_engine from sqlalchemy.engine import url as sqla_url from .compat import callable, EncodedIO from . import ddl, util log = logging.getLogger(__name__) class MigrationContext(object): """Represent the database state made available to a migration script. :class:`.MigrationContext` is the front end to an actual database connection, or alternatively a string output stream given a particular database dialect, from an Alembic perspective. When inside the ``env.py`` script, the :class:`.MigrationContext` is available via the :meth:`.EnvironmentContext.get_context` method, which is available at ``alembic.context``:: # from within env.py script from alembic import context migration_context = context.get_context() For usage outside of an ``env.py`` script, such as for utility routines that want to check the current version in the database, the :meth:`.MigrationContext.configure` method to create new :class:`.MigrationContext` objects. For example, to get at the current revision in the database using :meth:`.MigrationContext.get_current_revision`:: # in any application, outside of an env.py script from alembic.migration import MigrationContext from sqlalchemy import create_engine engine = create_engine("postgresql://mydatabase") conn = engine.connect() context = MigrationContext.configure(conn) current_rev = context.get_current_revision() The above context can also be used to produce Alembic migration operations with an :class:`.Operations` instance:: # in any application, outside of the normal Alembic environment from alembic.operations import Operations op = Operations(context) op.alter_column("mytable", "somecolumn", nullable=True) """ def __init__(self, dialect, connection, opts): self.opts = opts self.dialect = dialect self.script = opts.get('script') as_sql = opts.get('as_sql', False) transactional_ddl = opts.get("transactional_ddl") self._transaction_per_migration = opts.get( "transaction_per_migration", False) if as_sql: self.connection = self._stdout_connection(connection) assert self.connection is not None else: self.connection = connection self._migrations_fn = opts.get('fn') self.as_sql = as_sql if "output_encoding" in opts: self.output_buffer = EncodedIO( opts.get("output_buffer") or sys.stdout, opts['output_encoding'] ) else: self.output_buffer = opts.get("output_buffer", sys.stdout) self._user_compare_type = opts.get('compare_type', False) self._user_compare_server_default = opts.get( 'compare_server_default', False) version_table = opts.get('version_table', 'alembic_version') version_table_schema = opts.get('version_table_schema', None) self._version = Table( version_table, MetaData(), Column('version_num', String(32), nullable=False), schema=version_table_schema) self._start_from_rev = opts.get("starting_rev") self.impl = ddl.DefaultImpl.get_by_dialect(dialect)( dialect, self.connection, self.as_sql, transactional_ddl, self.output_buffer, opts ) log.info("Context impl %s.", self.impl.__class__.__name__) if self.as_sql: log.info("Generating static SQL") log.info("Will assume %s DDL.", "transactional" if self.impl.transactional_ddl else "non-transactional") @classmethod def configure(cls, connection=None, url=None, dialect_name=None, opts={}, ): """Create a new :class:`.MigrationContext`. This is a factory method usually called by :meth:`.EnvironmentContext.configure`. :param connection: a :class:`~sqlalchemy.engine.Connection` to use for SQL execution in "online" mode. When present, is also used to determine the type of dialect in use. :param url: a string database url, or a :class:`sqlalchemy.engine.url.URL` object. The type of dialect to be used will be derived from this if ``connection`` is not passed. :param dialect_name: string name of a dialect, such as "postgresql", "mssql", etc. The type of dialect to be used will be derived from this if ``connection`` and ``url`` are not passed. :param opts: dictionary of options. Most other options accepted by :meth:`.EnvironmentContext.configure` are passed via this dictionary. """ if connection: dialect = connection.dialect elif url: url = sqla_url.make_url(url) dialect = url.get_dialect()() elif dialect_name: url = sqla_url.make_url("%s://" % dialect_name) dialect = url.get_dialect()() else: raise Exception("Connection, url, or dialect_name is required.") return MigrationContext(dialect, connection, opts) def begin_transaction(self, _per_migration=False): transaction_now = _per_migration == self._transaction_per_migration if not transaction_now: @contextmanager def do_nothing(): yield return do_nothing() elif not self.impl.transactional_ddl: @contextmanager def do_nothing(): yield return do_nothing() elif self.as_sql: @contextmanager def begin_commit(): self.impl.emit_begin() yield self.impl.emit_commit() return begin_commit() else: return self.bind.begin() def get_current_revision(self): """Return the current revision, usually that which is present in the ``alembic_version`` table in the database. If this :class:`.MigrationContext` was configured in "offline" mode, that is with ``as_sql=True``, the ``starting_rev`` parameter is returned instead, if any. """ if self.as_sql: return self._start_from_rev else: if self._start_from_rev: raise util.CommandError( "Can't specify current_rev to context " "when using a database connection") self._version.create(self.connection, checkfirst=True) return self.connection.scalar(self._version.select()) _current_rev = get_current_revision """The 0.2 method name, for backwards compat.""" def _update_current_rev(self, old, new): if old == new: return if new is None: self.impl._exec(self._version.delete()) elif old is None: self.impl._exec(self._version.insert(). values(version_num=literal_column("'%s'" % new)) ) else: self.impl._exec(self._version.update(). values(version_num=literal_column("'%s'" % new)) ) def run_migrations(self, **kw): """Run the migration scripts established for this :class:`.MigrationContext`, if any. The commands in :mod:`alembic.command` will set up a function that is ultimately passed to the :class:`.MigrationContext` as the ``fn`` argument. This function represents the "work" that will be done when :meth:`.MigrationContext.run_migrations` is called, typically from within the ``env.py`` script of the migration environment. The "work function" then provides an iterable of version callables and other version information which in the case of the ``upgrade`` or ``downgrade`` commands are the list of version scripts to invoke. Other commands yield nothing, in the case that a command wants to run some other operation against the database such as the ``current`` or ``stamp`` commands. :param \**kw: keyword arguments here will be passed to each migration callable, that is the ``upgrade()`` or ``downgrade()`` method within revision scripts. """ current_rev = rev = False stamp_per_migration = not self.impl.transactional_ddl or \ self._transaction_per_migration self.impl.start_migrations() for change, prev_rev, rev, doc in self._migrations_fn( self.get_current_revision(), self): with self.begin_transaction(_per_migration=True): if current_rev is False: current_rev = prev_rev if self.as_sql and not current_rev: self._version.create(self.connection) if doc: log.info("Running %s %s -> %s, %s", change.__name__, prev_rev, rev, doc) else: log.info("Running %s %s -> %s", change.__name__, prev_rev, rev) if self.as_sql: self.impl.static_output( "-- Running %s %s -> %s" % (change.__name__, prev_rev, rev) ) change(**kw) if stamp_per_migration: self._update_current_rev(prev_rev, rev) prev_rev = rev if rev is not False: if not stamp_per_migration: self._update_current_rev(current_rev, rev) if self.as_sql and not rev: self._version.drop(self.connection) def execute(self, sql, execution_options=None): """Execute a SQL construct or string statement. The underlying execution mechanics are used, that is if this is "offline mode" the SQL is written to the output buffer, otherwise the SQL is emitted on the current SQLAlchemy connection. """ self.impl._exec(sql, execution_options) def _stdout_connection(self, connection): def dump(construct, *multiparams, **params): self.impl._exec(construct) return create_engine("%s://" % self.dialect.name, strategy="mock", executor=dump) @property def bind(self): """Return the current "bind". In online mode, this is an instance of :class:`sqlalchemy.engine.Connection`, and is suitable for ad-hoc execution of any kind of usage described in :ref:`sqlexpression_toplevel` as well as for usage with the :meth:`sqlalchemy.schema.Table.create` and :meth:`sqlalchemy.schema.MetaData.create_all` methods of :class:`~sqlalchemy.schema.Table`, :class:`~sqlalchemy.schema.MetaData`. Note that when "standard output" mode is enabled, this bind will be a "mock" connection handler that cannot return results and is only appropriate for a very limited subset of commands. """ return self.connection def _compare_type(self, inspector_column, metadata_column): if self._user_compare_type is False: return False if callable(self._user_compare_type): user_value = self._user_compare_type( self, inspector_column, metadata_column, inspector_column.type, metadata_column.type ) if user_value is not None: return user_value return self.impl.compare_type( inspector_column, metadata_column) def _compare_server_default(self, inspector_column, metadata_column, rendered_metadata_default, rendered_column_default): if self._user_compare_server_default is False: return False if callable(self._user_compare_server_default): user_value = self._user_compare_server_default( self, inspector_column, metadata_column, rendered_column_default, metadata_column.server_default, rendered_metadata_default ) if user_value is not None: return user_value return self.impl.compare_server_default( inspector_column, metadata_column, rendered_metadata_default, rendered_column_default)