import logging import sys from contextlib import contextmanager from collections import namedtuple 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, string_types from . import ddl, util from .revision import tuple_rev_as_scalar 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, environment_context=None): self.environment_context = environment_context 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) self.version_table = version_table = opts.get( 'version_table', 'alembic_version') self.version_table_schema = 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, environment_context=None, opts=None, ): """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 opts is None: opts = {} 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, environment_context) 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. This method intends to be used only for a migration stream that does not contain unmerged branches in the target database; if there are multiple branches present, an exception is raised. The :meth:`.MigrationContext.get_current_heads` should be preferred over this method going forward in order to be compatible with branch migration support. If this :class:`.MigrationContext` was configured in "offline" mode, that is with ``as_sql=True``, the ``starting_rev`` parameter is returned instead, if any. """ heads = self.get_current_heads() if len(heads) == 0: return None elif len(heads) > 1: raise util.CommandError( "Version table '%s' has more than one head present; " "please use get_current_heads()" % self.version_table) else: return heads[0] def get_current_heads(self): """Return a tuple of the current 'head versions' that are represented in the target database. For a migration stream without branches, this will be a single value, synonymous with that of :meth:`.MigrationContext.get_current_revision`. However when multiple unmerged branches exist within the target database, the returned tuple will contain a value for each head. If this :class:`.MigrationContext` was configured in "offline" mode, that is with ``as_sql=True``, the ``starting_rev`` parameter is returned in a one-length tuple. If no version table is present, or if there are no revisions present, an empty tuple is returned. .. versionadded:: 0.7.0 """ if self.as_sql: return util.to_tuple(self._start_from_rev, default=()) else: if self._start_from_rev: raise util.CommandError( "Can't specify current_rev to context " "when using a database connection") if not self._has_version_table(): return () return tuple( row[0] for row in self.connection.execute(self._version.select()) ) def _ensure_version_table(self): self._version.create(self.connection, checkfirst=True) def _has_version_table(self): return self.connection.dialect.has_table( self.connection, self.version_table, self.version_table_schema) def stamp(self, script_directory, revision): """Stamp the version table with a specific revision. This method calculates those branches to which the given revision can apply, and updates those branches as though they were migrated towards that revision (either up or down). If no current branches include the revision, it is added as a new branch head. .. versionadded:: 0.7.0 """ heads = self.get_current_heads() head_maintainer = HeadMaintainer(self, heads) for step in script_directory._steps_revs(revision, heads): head_maintainer.update_to_step(step) 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. """ self.impl.start_migrations() heads = self.get_current_heads() if not self.as_sql and not heads: self._ensure_version_table() head_maintainer = HeadMaintainer(self, heads) for step in self._migrations_fn(heads, self): with self.begin_transaction(_per_migration=True): if self.as_sql and not head_maintainer.heads: # for offline mode, include a CREATE TABLE from # the base self._version.create(self.connection) log.info("Running %s", step) if self.as_sql: self.impl.static_output("-- Running %s" % (step.short_log,)) step.migration_fn(**kw) # previously, we wouldn't stamp per migration # if we were in a transaction, however given the more # complex model that involves any number of inserts # and row-targeted updates and deletes, it's simpler for now # just to run the operations on every version head_maintainer.update_to_step(step) if self.as_sql and not head_maintainer.heads: 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 @property def config(self): """Return the :class:`.Config` used by the current environment, if any. .. versionadded:: 0.6.6 """ if self.environment_context: return self.environment_context.config else: return None 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) class HeadMaintainer(object): def __init__(self, context, heads): self.context = context self.heads = set(heads) def _insert_version(self, version): assert version not in self.heads self.heads.add(version) self.context.impl._exec( self.context._version.insert(). values( version_num=literal_column("'%s'" % version) ) ) def _delete_version(self, version): self.heads.remove(version) ret = self.context.impl._exec( self.context._version.delete().where( self.context._version.c.version_num == literal_column("'%s'" % version))) if not self.context.as_sql and ret.rowcount != 1: raise util.CommandError( "Online migration expected to match one " "row when deleting '%s' in '%s'; " "%d found" % (version, self.context.version_table, ret.rowcount)) def _update_version(self, from_, to_): assert to_ not in self.heads self.heads.remove(from_) self.heads.add(to_) ret = self.context.impl._exec( self.context._version.update(). values(version_num=literal_column("'%s'" % to_)).where( self.context._version.c.version_num == literal_column("'%s'" % from_)) ) if not self.context.as_sql and ret.rowcount != 1: raise util.CommandError( "Online migration expected to match one " "row when updating '%s' to '%s' in '%s'; " "%d found" % (from_, to_, self.context.version_table, ret.rowcount)) def update_to_step(self, step): if step.should_delete_branch(self.heads): vers = step.delete_version_num log.debug("branch delete %s", vers) self._delete_version(vers) elif step.should_create_branch(self.heads): vers = step.insert_version_num log.debug("new branch insert %s", vers) self._insert_version(vers) elif step.should_merge_branches(self.heads): # delete revs, update from rev, update to rev (delete_revs, update_from_rev, update_to_rev) = step.merge_branch_idents log.debug( "merge, delete %s, update %s to %s", delete_revs, update_from_rev, update_to_rev) for delrev in delete_revs: self._delete_version(delrev) self._update_version(update_from_rev, update_to_rev) elif step.should_unmerge_branches(self.heads): (update_from_rev, update_to_rev, insert_revs) = step.unmerge_branch_idents log.debug( "unmerge, insert %s, update %s to %s", insert_revs, update_from_rev, update_to_rev) for insrev in insert_revs: self._insert_version(insrev) self._update_version(update_from_rev, update_to_rev) else: from_, to_ = step.update_version_num log.debug("update %s to %s", from_, to_) self._update_version(from_, to_) class MigrationStep(object): @property def name(self): return self.migration_fn.__name__ @classmethod def upgrade_from_script(cls, revision_map, script): return RevisionStep(revision_map, script, True) @classmethod def downgrade_from_script(cls, revision_map, script): return RevisionStep(revision_map, script, False) @property def short_log(self): return "%s %s -> %s" % ( self.name, tuple_rev_as_scalar(self.from_revisions), tuple_rev_as_scalar(self.to_revisions) ) def __str__(self): if self.doc: return "%s %s -> %s, %s" % ( self.name, tuple_rev_as_scalar(self.from_revisions), tuple_rev_as_scalar(self.to_revisions), self.doc ) else: return self.short_log class RevisionStep(MigrationStep): def __init__(self, revision_map, revision, is_upgrade): self.revision_map = revision_map self.revision = revision self.is_upgrade = is_upgrade if is_upgrade: self.migration_fn = revision.module.upgrade else: self.migration_fn = revision.module.downgrade def __eq__(self, other): return isinstance(other, RevisionStep) and \ other.revision == self.revision and \ self.is_upgrade == other.is_upgrade @property def doc(self): return self.revision.doc @property def from_revisions(self): if self.is_upgrade: return self.revision._down_revision_tuple else: return (self.revision.revision, ) @property def to_revisions(self): if self.is_upgrade: return (self.revision.revision, ) else: return self.revision._down_revision_tuple @property def is_downgrade(self): return not self.is_upgrade @property def _has_scalar_down_revision(self): return len(self.revision._down_revision_tuple) == 1 def should_delete_branch(self, heads): if not self.is_downgrade: return False if self.revision.revision not in heads: return False downrevs = self.revision._down_revision_tuple if not downrevs: # is a base return True elif len(downrevs) == 1: downrev = self.revision_map.get_revision(downrevs[0]) if not downrev.is_branch_point: return False descendants = set( r.revision for r in self.revision_map._get_descendant_nodes( self.revision_map.get_revisions(downrev.nextrev), check=False ) ) # the downrev is a branchpoint, and other members or descendants # of the branch are still in heads; so delete this branch. # the reason this occurs is because traversal tries to stay # fully on one branch down to the branchpoint before starting # the other; so if we have a->b->(c1->d1->e1, c2->d2->e2), # on a downgrade from the top we may go e1, d1, c1, now heads # are at c1 and e2, with the current method, we don't know that # "e2" is important unless we get all descendants of c1/c2 if len(descendants.intersection(heads).difference( [self.revision.revision])): # TODO: this doesn't work; make sure tests are here to ensure # this fails #if len(downrev.nextrev.intersection(heads).difference( # [self.revision.revision])): return True else: return False else: # is a merge point return False def should_create_branch(self, heads): if not self.is_upgrade: return False downrevs = self.revision._down_revision_tuple if not downrevs: # is a base return True elif len(downrevs) == 1: if downrevs[0] in heads: return False else: return True else: # is a merge point return False def should_merge_branches(self, heads): if not self.is_upgrade: return False downrevs = self.revision._down_revision_tuple if len(downrevs) > 1 and \ len(heads.intersection(downrevs)) > 1: return True return False def should_unmerge_branches(self, heads): if not self.is_downgrade: return False downrevs = self.revision._down_revision_tuple if self.revision.revision in heads and len(downrevs) > 1: return True return False @property def update_version_num(self): assert self._has_scalar_down_revision if self.is_upgrade: return self.revision.down_revision, self.revision.revision else: return self.revision.revision, self.revision.down_revision @property def delete_version_num(self): return self.revision.revision @property def insert_version_num(self): return self.revision.revision @property def merge_branch_idents(self): return ( # delete revs, update from rev, update to rev self.from_revisions[0:-1], self.from_revisions[-1], self.to_revisions[0] ) @property def unmerge_branch_idents(self): return ( # update from rev, update to rev, insert revs self.from_revisions[0], self.to_revisions[-1], self.to_revisions[0:-1] ) class StampStep(MigrationStep): pass