openmedialibrary_platform/Darwin/lib/python2.7/site-packages/alembic/migration.py

353 lines
13 KiB
Python
Raw Normal View History

2013-10-11 17:28:32 +00:00
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)