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"""Provide the 'autogenerate' feature which can produce migration operations
automatically."""
from ..operations import ops
from . import render
from . import compare
from .. import util
from sqlalchemy.engine.reflection import Inspector
import contextlib
def compare_metadata(context, metadata):
"""Compare a database schema to that given in a
:class:`~sqlalchemy.schema.MetaData` instance.
The database connection is presented in the context
of a :class:`.MigrationContext` object, which
provides database connectivity as well as optional
comparison functions to use for datatypes and
server defaults - see the "autogenerate" arguments
at :meth:`.EnvironmentContext.configure`
for details on these.
The return format is a list of "diff" directives,
each representing individual differences::
from alembic.migration import MigrationContext
from alembic.autogenerate import compare_metadata
from sqlalchemy.schema import SchemaItem
from sqlalchemy.types import TypeEngine
from sqlalchemy import (create_engine, MetaData, Column,
Integer, String, Table)
import pprint
engine = create_engine("sqlite://")
engine.execute('''
create table foo (
id integer not null primary key,
old_data varchar,
x integer
)''')
engine.execute('''
create table bar (
data varchar
)''')
metadata = MetaData()
Table('foo', metadata,
Column('id', Integer, primary_key=True),
Column('data', Integer),
Column('x', Integer, nullable=False)
)
Table('bat', metadata,
Column('info', String)
)
mc = MigrationContext.configure(engine.connect())
diff = compare_metadata(mc, metadata)
pprint.pprint(diff, indent=2, width=20)
Output::
[ ( 'add_table',
Table('bat', MetaData(bind=None),
Column('info', String(), table=<bat>), schema=None)),
( 'remove_table',
Table(u'bar', MetaData(bind=None),
Column(u'data', VARCHAR(), table=<bar>), schema=None)),
( 'add_column',
None,
'foo',
Column('data', Integer(), table=<foo>)),
( 'remove_column',
None,
'foo',
Column(u'old_data', VARCHAR(), table=None)),
[ ( 'modify_nullable',
None,
'foo',
u'x',
{ 'existing_server_default': None,
'existing_type': INTEGER()},
True,
False)]]
:param context: a :class:`.MigrationContext`
instance.
:param metadata: a :class:`~sqlalchemy.schema.MetaData`
instance.
.. seealso::
:func:`.produce_migrations` - produces a :class:`.MigrationScript`
structure based on metadata comparison.
"""
migration_script = produce_migrations(context, metadata)
return migration_script.upgrade_ops.as_diffs()
def produce_migrations(context, metadata):
"""Produce a :class:`.MigrationScript` structure based on schema
comparison.
This function does essentially what :func:`.compare_metadata` does,
but then runs the resulting list of diffs to produce the full
:class:`.MigrationScript` object. For an example of what this looks like,
see the example in :ref:`customizing_revision`.
.. versionadded:: 0.8.0
.. seealso::
:func:`.compare_metadata` - returns more fundamental "diff"
data from comparing a schema.
"""
autogen_context = AutogenContext(context, metadata=metadata)
migration_script = ops.MigrationScript(
rev_id=None,
upgrade_ops=ops.UpgradeOps([]),
downgrade_ops=ops.DowngradeOps([]),
)
compare._populate_migration_script(autogen_context, migration_script)
return migration_script
def render_python_code(
up_or_down_op,
sqlalchemy_module_prefix='sa.',
alembic_module_prefix='op.',
render_as_batch=False,
imports=(),
render_item=None,
):
"""Render Python code given an :class:`.UpgradeOps` or
:class:`.DowngradeOps` object.
This is a convenience function that can be used to test the
autogenerate output of a user-defined :class:`.MigrationScript` structure.
"""
opts = {
'sqlalchemy_module_prefix': sqlalchemy_module_prefix,
'alembic_module_prefix': alembic_module_prefix,
'render_item': render_item,
'render_as_batch': render_as_batch,
}
autogen_context = AutogenContext(None, opts=opts)
autogen_context.imports = set(imports)
return render._indent(render._render_cmd_body(
up_or_down_op, autogen_context))
def _render_migration_diffs(context, template_args):
"""legacy, used by test_autogen_composition at the moment"""
autogen_context = AutogenContext(context)
upgrade_ops = ops.UpgradeOps([])
compare._produce_net_changes(autogen_context, upgrade_ops)
migration_script = ops.MigrationScript(
rev_id=None,
upgrade_ops=upgrade_ops,
downgrade_ops=upgrade_ops.reverse(),
)
render._render_python_into_templatevars(
autogen_context, migration_script, template_args
)
class AutogenContext(object):
"""Maintains configuration and state that's specific to an
autogenerate operation."""
metadata = None
"""The :class:`~sqlalchemy.schema.MetaData` object
representing the destination.
This object is the one that is passed within ``env.py``
to the :paramref:`.EnvironmentContext.configure.target_metadata`
parameter. It represents the structure of :class:`.Table` and other
objects as stated in the current database model, and represents the
destination structure for the database being examined.
While the :class:`~sqlalchemy.schema.MetaData` object is primarily
known as a collection of :class:`~sqlalchemy.schema.Table` objects,
it also has an :attr:`~sqlalchemy.schema.MetaData.info` dictionary
that may be used by end-user schemes to store additional schema-level
objects that are to be compared in custom autogeneration schemes.
"""
connection = None
"""The :class:`~sqlalchemy.engine.base.Connection` object currently
connected to the database backend being compared.
This is obtained from the :attr:`.MigrationContext.bind` and is
utimately set up in the ``env.py`` script.
"""
dialect = None
"""The :class:`~sqlalchemy.engine.Dialect` object currently in use.
This is normally obtained from the
:attr:`~sqlalchemy.engine.base.Connection.dialect` attribute.
"""
imports = None
"""A ``set()`` which contains string Python import directives.
The directives are to be rendered into the ``${imports}`` section
of a script template. The set is normally empty and can be modified
within hooks such as the :paramref:`.EnvironmentContext.configure.render_item`
hook.
.. versionadded:: 0.8.3
.. seealso::
:ref:`autogen_render_types`
"""
migration_context = None
"""The :class:`.MigrationContext` established by the ``env.py`` script."""
def __init__(
self, migration_context, metadata=None,
opts=None, autogenerate=True):
if autogenerate and \
migration_context is not None and migration_context.as_sql:
raise util.CommandError(
"autogenerate can't use as_sql=True as it prevents querying "
"the database for schema information")
if opts is None:
opts = migration_context.opts
self.metadata = metadata = opts.get('target_metadata', None) \
if metadata is None else metadata
if metadata is None and \
migration_context is not None and \
migration_context.script is not None:
raise util.CommandError(
"Can't proceed with --autogenerate option; environment "
"script %s does not provide "
"a MetaData object to the context." % (
migration_context.script.env_py_location
))
include_symbol = opts.get('include_symbol', None)
include_object = opts.get('include_object', None)
object_filters = []
if include_symbol:
def include_symbol_filter(
object, name, type_, reflected, compare_to):
if type_ == "table":
return include_symbol(name, object.schema)
else:
return True
object_filters.append(include_symbol_filter)
if include_object:
object_filters.append(include_object)
self._object_filters = object_filters
self.migration_context = migration_context
if self.migration_context is not None:
self.connection = self.migration_context.bind
self.dialect = self.migration_context.dialect
self.imports = set()
self.opts = opts
self._has_batch = False
@util.memoized_property
def inspector(self):
return Inspector.from_engine(self.connection)
@contextlib.contextmanager
def _within_batch(self):
self._has_batch = True
yield
self._has_batch = False
def run_filters(self, object_, name, type_, reflected, compare_to):
"""Run the context's object filters and return True if the targets
should be part of the autogenerate operation.
This method should be run for every kind of object encountered within
an autogenerate operation, giving the environment the chance
to filter what objects should be included in the comparison.
The filters here are produced directly via the
:paramref:`.EnvironmentContext.configure.include_object`
and :paramref:`.EnvironmentContext.configure.include_symbol`
functions, if present.
"""
for fn in self._object_filters:
if not fn(object_, name, type_, reflected, compare_to):
return False
else:
return True
class RevisionContext(object):
"""Maintains configuration and state that's specific to a revision
file generation operation."""
def __init__(self, config, script_directory, command_args):
self.config = config
self.script_directory = script_directory
self.command_args = command_args
self.template_args = {
'config': config # Let templates use config for
# e.g. multiple databases
}
self.generated_revisions = [
self._default_revision()
]
def _to_script(self, migration_script):
template_args = {}
for k, v in self.template_args.items():
template_args.setdefault(k, v)
if getattr(migration_script, '_needs_render', False):
autogen_context = self._last_autogen_context
# clear out existing imports if we are doing multiple
# renders
autogen_context.imports = set()
if migration_script.imports:
autogen_context.imports.union_update(migration_script.imports)
render._render_python_into_templatevars(
autogen_context, migration_script, template_args
)
return self.script_directory.generate_revision(
migration_script.rev_id,
migration_script.message,
refresh=True,
head=migration_script.head,
splice=migration_script.splice,
branch_labels=migration_script.branch_label,
version_path=migration_script.version_path,
depends_on=migration_script.depends_on,
**template_args)
def run_autogenerate(self, rev, migration_context):
self._run_environment(rev, migration_context, True)
def run_no_autogenerate(self, rev, migration_context):
self._run_environment(rev, migration_context, False)
def _run_environment(self, rev, migration_context, autogenerate):
if autogenerate:
if self.command_args['sql']:
raise util.CommandError(
"Using --sql with --autogenerate does not make any sense")
if set(self.script_directory.get_revisions(rev)) != \
set(self.script_directory.get_revisions("heads")):
raise util.CommandError("Target database is not up to date.")
upgrade_token = migration_context.opts['upgrade_token']
downgrade_token = migration_context.opts['downgrade_token']
migration_script = self.generated_revisions[-1]
if not getattr(migration_script, '_needs_render', False):
migration_script.upgrade_ops_list[-1].upgrade_token = upgrade_token
migration_script.downgrade_ops_list[-1].downgrade_token = \
downgrade_token
migration_script._needs_render = True
else:
migration_script._upgrade_ops.append(
ops.UpgradeOps([], upgrade_token=upgrade_token)
)
migration_script._downgrade_ops.append(
ops.DowngradeOps([], downgrade_token=downgrade_token)
)
self._last_autogen_context = autogen_context = \
AutogenContext(migration_context, autogenerate=autogenerate)
if autogenerate:
compare._populate_migration_script(
autogen_context, migration_script)
hook = migration_context.opts['process_revision_directives']
if hook:
hook(migration_context, rev, self.generated_revisions)
for migration_script in self.generated_revisions:
migration_script._needs_render = True
def _default_revision(self):
op = ops.MigrationScript(
rev_id=self.command_args['rev_id'] or util.rev_id(),
message=self.command_args['message'],
upgrade_ops=ops.UpgradeOps([]),
downgrade_ops=ops.DowngradeOps([]),
head=self.command_args['head'],
splice=self.command_args['splice'],
branch_label=self.command_args['branch_label'],
version_path=self.command_args['version_path'],
depends_on=self.command_args['depends_on']
)
return op
def generate_scripts(self):
for generated_revision in self.generated_revisions:
yield self._to_script(generated_revision)
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