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# sql/ddl.py
# Copyright (C) 2009-2021 the SQLAlchemy authors and contributors
# <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php
"""
Provides the hierarchy of DDL-defining schema items as well as routines
to invoke them for a create/drop call.
"""
from .base import _bind_or_error
from .base import _generative
from .base import Executable
from .base import SchemaVisitor
from .elements import ClauseElement
from .. import event
from .. import exc
from .. import util
from ..util import topological
class _DDLCompiles(ClauseElement):
def _compiler(self, dialect, **kw):
"""Return a compiler appropriate for this ClauseElement, given a
Dialect."""
return dialect.ddl_compiler(dialect, self, **kw)
class DDLElement(Executable, _DDLCompiles):
"""Base class for DDL expression constructs.
This class is the base for the general purpose :class:`.DDL` class,
as well as the various create/drop clause constructs such as
:class:`.CreateTable`, :class:`.DropTable`, :class:`.AddConstraint`,
etc.
:class:`.DDLElement` integrates closely with SQLAlchemy events,
introduced in :ref:`event_toplevel`. An instance of one is
itself an event receiving callable::
event.listen(
users,
'after_create',
AddConstraint(constraint).execute_if(dialect='postgresql')
)
.. seealso::
:class:`.DDL`
:class:`.DDLEvents`
:ref:`event_toplevel`
:ref:`schema_ddl_sequences`
"""
_execution_options = Executable._execution_options.union(
{"autocommit": True}
)
target = None
on = None
dialect = None
callable_ = None
def _execute_on_connection(self, connection, multiparams, params):
return connection._execute_ddl(self, multiparams, params)
def execute(self, bind=None, target=None):
"""Execute this DDL immediately.
Executes the DDL statement in isolation using the supplied
:class:`.Connectable` or
:class:`.Connectable` assigned to the ``.bind``
property, if not supplied. If the DDL has a conditional ``on``
criteria, it will be invoked with None as the event.
:param bind:
Optional, an ``Engine`` or ``Connection``. If not supplied, a valid
:class:`.Connectable` must be present in the
``.bind`` property.
:param target:
Optional, defaults to None. The target :class:`_schema.SchemaItem`
for the execute call. Will be passed to the ``on`` callable if any,
and may also provide string expansion data for the statement.
See ``execute_at`` for more information.
"""
if bind is None:
bind = _bind_or_error(self)
if self._should_execute(target, bind):
return bind.execute(self.against(target))
else:
bind.engine.logger.info("DDL execution skipped, criteria not met.")
@util.deprecated(
"0.7",
"The :meth:`.DDLElement.execute_at` method is deprecated and will "
"be removed in a future release. Please use the :class:`.DDLEvents` "
"listener interface in conjunction with the "
":meth:`.DDLElement.execute_if` method.",
)
def execute_at(self, event_name, target):
"""Link execution of this DDL to the DDL lifecycle of a SchemaItem.
Links this ``DDLElement`` to a ``Table`` or ``MetaData`` instance,
executing it when that schema item is created or dropped. The DDL
statement will be executed using the same Connection and transactional
context as the Table create/drop itself. The ``.bind`` property of
this statement is ignored.
:param event:
One of the events defined in the schema item's ``.ddl_events``;
e.g. 'before-create', 'after-create', 'before-drop' or 'after-drop'
:param target:
The Table or MetaData instance for which this DDLElement will
be associated with.
A DDLElement instance can be linked to any number of schema items.
``execute_at`` builds on the ``append_ddl_listener`` interface of
:class:`_schema.MetaData` and :class:`_schema.Table` objects.
Caveat: Creating or dropping a Table in isolation will also trigger
any DDL set to ``execute_at`` that Table's MetaData. This may change
in a future release.
"""
def call_event(target, connection, **kw):
if self._should_execute_deprecated(
event_name, target, connection, **kw
):
return connection.execute(self.against(target))
event.listen(target, "" + event_name.replace("-", "_"), call_event)
@_generative
def against(self, target):
"""Return a copy of this DDL against a specific schema item."""
self.target = target
@_generative
def execute_if(self, dialect=None, callable_=None, state=None):
r"""Return a callable that will execute this
DDLElement conditionally.
Used to provide a wrapper for event listening::
event.listen(
metadata,
'before_create',
DDL("my_ddl").execute_if(dialect='postgresql')
)
:param dialect: May be a string, tuple or a callable
predicate. If a string, it will be compared to the name of the
executing database dialect::
DDL('something').execute_if(dialect='postgresql')
If a tuple, specifies multiple dialect names::
DDL('something').execute_if(dialect=('postgresql', 'mysql'))
:param callable\_: A callable, which will be invoked with
four positional arguments as well as optional keyword
arguments:
:ddl:
This DDL element.
:target:
The :class:`_schema.Table` or :class:`_schema.MetaData`
object which is the
target of this event. May be None if the DDL is executed
explicitly.
:bind:
The :class:`_engine.Connection` being used for DDL execution
:tables:
Optional keyword argument - a list of Table objects which are to
be created/ dropped within a MetaData.create_all() or drop_all()
method call.
:state:
Optional keyword argument - will be the ``state`` argument
passed to this function.
:checkfirst:
Keyword argument, will be True if the 'checkfirst' flag was
set during the call to ``create()``, ``create_all()``,
``drop()``, ``drop_all()``.
If the callable returns a True value, the DDL statement will be
executed.
:param state: any value which will be passed to the callable\_
as the ``state`` keyword argument.
.. seealso::
:class:`.DDLEvents`
:ref:`event_toplevel`
"""
self.dialect = dialect
self.callable_ = callable_
self.state = state
def _should_execute(self, target, bind, **kw):
if self.on is not None and not self._should_execute_deprecated(
None, target, bind, **kw
):
return False
if isinstance(self.dialect, util.string_types):
if self.dialect != bind.engine.name:
return False
elif isinstance(self.dialect, (tuple, list, set)):
if bind.engine.name not in self.dialect:
return False
if self.callable_ is not None and not self.callable_(
self, target, bind, state=self.state, **kw
):
return False
return True
def _should_execute_deprecated(self, event, target, bind, **kw):
if self.on is None:
return True
elif isinstance(self.on, util.string_types):
return self.on == bind.engine.name
elif isinstance(self.on, (tuple, list, set)):
return bind.engine.name in self.on
else:
return self.on(self, event, target, bind, **kw)
def __call__(self, target, bind, **kw):
"""Execute the DDL as a ddl_listener."""
if self._should_execute(target, bind, **kw):
return bind.execute(self.against(target))
def _check_ddl_on(self, on):
if on is not None and (
not isinstance(on, util.string_types + (tuple, list, set))
and not util.callable(on)
):
raise exc.ArgumentError(
"Expected the name of a database dialect, a tuple "
"of names, or a callable for "
"'on' criteria, got type '%s'." % type(on).__name__
)
def bind(self):
if self._bind:
return self._bind
def _set_bind(self, bind):
self._bind = bind
bind = property(bind, _set_bind)
def _generate(self):
s = self.__class__.__new__(self.__class__)
s.__dict__ = self.__dict__.copy()
return s
class DDL(DDLElement):
"""A literal DDL statement.
Specifies literal SQL DDL to be executed by the database. DDL objects
function as DDL event listeners, and can be subscribed to those events
listed in :class:`.DDLEvents`, using either :class:`_schema.Table` or
:class:`_schema.MetaData` objects as targets.
Basic templating support allows
a single DDL instance to handle repetitive tasks for multiple tables.
Examples::
from sqlalchemy import event, DDL
tbl = Table('users', metadata, Column('uid', Integer))
event.listen(tbl, 'before_create', DDL('DROP TRIGGER users_trigger'))
spow = DDL('ALTER TABLE %(table)s SET secretpowers TRUE')
event.listen(tbl, 'after_create', spow.execute_if(dialect='somedb'))
drop_spow = DDL('ALTER TABLE users SET secretpowers FALSE')
connection.execute(drop_spow)
When operating on Table events, the following ``statement``
string substitutions are available::
%(table)s - the Table name, with any required quoting applied
%(schema)s - the schema name, with any required quoting applied
%(fullname)s - the Table name including schema, quoted if needed
The DDL's "context", if any, will be combined with the standard
substitutions noted above. Keys present in the context will override
the standard substitutions.
"""
__visit_name__ = "ddl"
@util.deprecated_params(
on=(
"0.7",
"The :paramref:`.DDL.on` parameter is deprecated and will be "
"removed in a future release. Please refer to "
":meth:`.DDLElement.execute_if`.",
)
)
def __init__(self, statement, on=None, context=None, bind=None):
"""Create a DDL statement.
:param statement:
A string or unicode string to be executed. Statements will be
processed with Python's string formatting operator. See the
``context`` argument and the ``execute_at`` method.
A literal '%' in a statement must be escaped as '%%'.
SQL bind parameters are not available in DDL statements.
:param on:
Optional filtering criteria. May be a string, tuple or a callable
predicate. If a string, it will be compared to the name of the
executing database dialect::
DDL('something', on='postgresql')
If a tuple, specifies multiple dialect names::
DDL('something', on=('postgresql', 'mysql'))
If a callable, it will be invoked with four positional arguments
as well as optional keyword arguments:
:ddl:
This DDL element.
:event:
The name of the event that has triggered this DDL, such as
'after-create' Will be None if the DDL is executed explicitly.
:target:
The ``Table`` or ``MetaData`` object which is the target of
this event. May be None if the DDL is executed explicitly.
:connection:
The ``Connection`` being used for DDL execution
:tables:
Optional keyword argument - a list of Table objects which are to
be created/ dropped within a MetaData.create_all() or drop_all()
method call.
If the callable returns a true value, the DDL statement will be
executed.
:param context:
Optional dictionary, defaults to None. These values will be
available for use in string substitutions on the DDL statement.
:param bind:
Optional. A :class:`.Connectable`, used by
default when ``execute()`` is invoked without a bind argument.
.. seealso::
:class:`.DDLEvents`
:ref:`event_toplevel`
"""
if not isinstance(statement, util.string_types):
raise exc.ArgumentError(
"Expected a string or unicode SQL statement, got '%r'"
% statement
)
self.statement = statement
self.context = context or {}
self._check_ddl_on(on)
self.on = on
self._bind = bind
def __repr__(self):
return "<%s@%s; %s>" % (
type(self).__name__,
id(self),
", ".join(
[repr(self.statement)]
+ [
"%s=%r" % (key, getattr(self, key))
for key in ("on", "context")
if getattr(self, key)
]
),
)
class _CreateDropBase(DDLElement):
"""Base class for DDL constructs that represent CREATE and DROP or
equivalents.
The common theme of _CreateDropBase is a single
``element`` attribute which refers to the element
to be created or dropped.
"""
def __init__(self, element, on=None, bind=None):
self.element = element
self._check_ddl_on(on)
self.on = on
self.bind = bind
def _create_rule_disable(self, compiler):
"""Allow disable of _create_rule using a callable.
Pass to _create_rule using
util.portable_instancemethod(self._create_rule_disable)
to retain serializability.
"""
return False
class CreateSchema(_CreateDropBase):
"""Represent a CREATE SCHEMA statement.
The argument here is the string name of the schema.
"""
__visit_name__ = "create_schema"
def __init__(self, name, quote=None, **kw):
"""Create a new :class:`.CreateSchema` construct."""
self.quote = quote
super(CreateSchema, self).__init__(name, **kw)
class DropSchema(_CreateDropBase):
"""Represent a DROP SCHEMA statement.
The argument here is the string name of the schema.
"""
__visit_name__ = "drop_schema"
def __init__(self, name, quote=None, cascade=False, **kw):
"""Create a new :class:`.DropSchema` construct."""
self.quote = quote
self.cascade = cascade
super(DropSchema, self).__init__(name, **kw)
class CreateTable(_CreateDropBase):
"""Represent a CREATE TABLE statement."""
__visit_name__ = "create_table"
def __init__(
self, element, on=None, bind=None, include_foreign_key_constraints=None
):
"""Create a :class:`.CreateTable` construct.
:param element: a :class:`_schema.Table` that's the subject
of the CREATE
:param on: See the description for 'on' in :class:`.DDL`.
:param bind: See the description for 'bind' in :class:`.DDL`.
:param include_foreign_key_constraints: optional sequence of
:class:`_schema.ForeignKeyConstraint` objects that will be included
inline within the CREATE construct; if omitted, all foreign key
constraints that do not specify use_alter=True are included.
.. versionadded:: 1.0.0
"""
super(CreateTable, self).__init__(element, on=on, bind=bind)
self.columns = [CreateColumn(column) for column in element.columns]
self.include_foreign_key_constraints = include_foreign_key_constraints
class _DropView(_CreateDropBase):
"""Semi-public 'DROP VIEW' construct.
Used by the test suite for dialect-agnostic drops of views.
This object will eventually be part of a public "view" API.
"""
__visit_name__ = "drop_view"
class CreateColumn(_DDLCompiles):
"""Represent a :class:`_schema.Column`
as rendered in a CREATE TABLE statement,
via the :class:`.CreateTable` construct.
This is provided to support custom column DDL within the generation
of CREATE TABLE statements, by using the
compiler extension documented in :ref:`sqlalchemy.ext.compiler_toplevel`
to extend :class:`.CreateColumn`.
Typical integration is to examine the incoming :class:`_schema.Column`
object, and to redirect compilation if a particular flag or condition
is found::
from sqlalchemy import schema
from sqlalchemy.ext.compiler import compiles
@compiles(schema.CreateColumn)
def compile(element, compiler, **kw):
column = element.element
if "special" not in column.info:
return compiler.visit_create_column(element, **kw)
text = "%s SPECIAL DIRECTIVE %s" % (
column.name,
compiler.type_compiler.process(column.type)
)
default = compiler.get_column_default_string(column)
if default is not None:
text += " DEFAULT " + default
if not column.nullable:
text += " NOT NULL"
if column.constraints:
text += " ".join(
compiler.process(const)
for const in column.constraints)
return text
The above construct can be applied to a :class:`_schema.Table`
as follows::
from sqlalchemy import Table, Metadata, Column, Integer, String
from sqlalchemy import schema
metadata = MetaData()
table = Table('mytable', MetaData(),
Column('x', Integer, info={"special":True}, primary_key=True),
Column('y', String(50)),
Column('z', String(20), info={"special":True})
)
metadata.create_all(conn)
Above, the directives we've added to the :attr:`_schema.Column.info`
collection
will be detected by our custom compilation scheme::
CREATE TABLE mytable (
x SPECIAL DIRECTIVE INTEGER NOT NULL,
y VARCHAR(50),
z SPECIAL DIRECTIVE VARCHAR(20),
PRIMARY KEY (x)
)
The :class:`.CreateColumn` construct can also be used to skip certain
columns when producing a ``CREATE TABLE``. This is accomplished by
creating a compilation rule that conditionally returns ``None``.
This is essentially how to produce the same effect as using the
``system=True`` argument on :class:`_schema.Column`, which marks a column
as an implicitly-present "system" column.
For example, suppose we wish to produce a :class:`_schema.Table`
which skips
rendering of the PostgreSQL ``xmin`` column against the PostgreSQL
backend, but on other backends does render it, in anticipation of a
triggered rule. A conditional compilation rule could skip this name only
on PostgreSQL::
from sqlalchemy.schema import CreateColumn
@compiles(CreateColumn, "postgresql")
def skip_xmin(element, compiler, **kw):
if element.element.name == 'xmin':
return None
else:
return compiler.visit_create_column(element, **kw)
my_table = Table('mytable', metadata,
Column('id', Integer, primary_key=True),
Column('xmin', Integer)
)
Above, a :class:`.CreateTable` construct will generate a ``CREATE TABLE``
which only includes the ``id`` column in the string; the ``xmin`` column
will be omitted, but only against the PostgreSQL backend.
"""
__visit_name__ = "create_column"
def __init__(self, element):
self.element = element
class DropTable(_CreateDropBase):
"""Represent a DROP TABLE statement."""
__visit_name__ = "drop_table"
class CreateSequence(_CreateDropBase):
"""Represent a CREATE SEQUENCE statement."""
__visit_name__ = "create_sequence"
class DropSequence(_CreateDropBase):
"""Represent a DROP SEQUENCE statement."""
__visit_name__ = "drop_sequence"
class CreateIndex(_CreateDropBase):
"""Represent a CREATE INDEX statement."""
__visit_name__ = "create_index"
class DropIndex(_CreateDropBase):
"""Represent a DROP INDEX statement."""
__visit_name__ = "drop_index"
class AddConstraint(_CreateDropBase):
"""Represent an ALTER TABLE ADD CONSTRAINT statement."""
__visit_name__ = "add_constraint"
def __init__(self, element, *args, **kw):
super(AddConstraint, self).__init__(element, *args, **kw)
element._create_rule = util.portable_instancemethod(
self._create_rule_disable
)
class DropConstraint(_CreateDropBase):
"""Represent an ALTER TABLE DROP CONSTRAINT statement."""
__visit_name__ = "drop_constraint"
def __init__(self, element, cascade=False, **kw):
self.cascade = cascade
super(DropConstraint, self).__init__(element, **kw)
element._create_rule = util.portable_instancemethod(
self._create_rule_disable
)
class SetTableComment(_CreateDropBase):
"""Represent a COMMENT ON TABLE IS statement."""
__visit_name__ = "set_table_comment"
class DropTableComment(_CreateDropBase):
"""Represent a COMMENT ON TABLE '' statement.
Note this varies a lot across database backends.
"""
__visit_name__ = "drop_table_comment"
class SetColumnComment(_CreateDropBase):
"""Represent a COMMENT ON COLUMN IS statement."""
__visit_name__ = "set_column_comment"
class DropColumnComment(_CreateDropBase):
"""Represent a COMMENT ON COLUMN IS NULL statement."""
__visit_name__ = "drop_column_comment"
class DDLBase(SchemaVisitor):
def __init__(self, connection):
self.connection = connection
class SchemaGenerator(DDLBase):
def __init__(
self, dialect, connection, checkfirst=False, tables=None, **kwargs
):
super(SchemaGenerator, self).__init__(connection, **kwargs)
self.checkfirst = checkfirst
self.tables = tables
self.preparer = dialect.identifier_preparer
self.dialect = dialect
self.memo = {}
def _can_create_table(self, table):
self.dialect.validate_identifier(table.name)
effective_schema = self.connection.schema_for_object(table)
if effective_schema:
self.dialect.validate_identifier(effective_schema)
return not self.checkfirst or not self.dialect.has_table(
self.connection, table.name, schema=effective_schema
)
def _can_create_sequence(self, sequence):
effective_schema = self.connection.schema_for_object(sequence)
return self.dialect.supports_sequences and (
(not self.dialect.sequences_optional or not sequence.optional)
and (
not self.checkfirst
or not self.dialect.has_sequence(
self.connection, sequence.name, schema=effective_schema
)
)
)
def visit_metadata(self, metadata):
if self.tables is not None:
tables = self.tables
else:
tables = list(metadata.tables.values())
collection = sort_tables_and_constraints(
[t for t in tables if self._can_create_table(t)]
)
seq_coll = [
s
for s in metadata._sequences.values()
if s.column is None and self._can_create_sequence(s)
]
event_collection = [t for (t, fks) in collection if t is not None]
metadata.dispatch.before_create(
metadata,
self.connection,
tables=event_collection,
checkfirst=self.checkfirst,
_ddl_runner=self,
)
for seq in seq_coll:
self.traverse_single(seq, create_ok=True)
for table, fkcs in collection:
if table is not None:
self.traverse_single(
table,
create_ok=True,
include_foreign_key_constraints=fkcs,
_is_metadata_operation=True,
)
else:
for fkc in fkcs:
self.traverse_single(fkc)
metadata.dispatch.after_create(
metadata,
self.connection,
tables=event_collection,
checkfirst=self.checkfirst,
_ddl_runner=self,
)
def visit_table(
self,
table,
create_ok=False,
include_foreign_key_constraints=None,
_is_metadata_operation=False,
):
if not create_ok and not self._can_create_table(table):
return
table.dispatch.before_create(
table,
self.connection,
checkfirst=self.checkfirst,
_ddl_runner=self,
_is_metadata_operation=_is_metadata_operation,
)
for column in table.columns:
if column.default is not None:
self.traverse_single(column.default)
if not self.dialect.supports_alter:
# e.g., don't omit any foreign key constraints
include_foreign_key_constraints = None
self.connection.execute(
# fmt: off
CreateTable(
table,
include_foreign_key_constraints= # noqa
include_foreign_key_constraints, # noqa
)
# fmt: on
)
if hasattr(table, "indexes"):
for index in table.indexes:
self.traverse_single(index)
if self.dialect.supports_comments and not self.dialect.inline_comments:
if table.comment is not None:
self.connection.execute(SetTableComment(table))
for column in table.columns:
if column.comment is not None:
self.connection.execute(SetColumnComment(column))
table.dispatch.after_create(
table,
self.connection,
checkfirst=self.checkfirst,
_ddl_runner=self,
_is_metadata_operation=_is_metadata_operation,
)
def visit_foreign_key_constraint(self, constraint):
if not self.dialect.supports_alter:
return
self.connection.execute(AddConstraint(constraint))
def visit_sequence(self, sequence, create_ok=False):
if not create_ok and not self._can_create_sequence(sequence):
return
self.connection.execute(CreateSequence(sequence))
def visit_index(self, index):
self.connection.execute(CreateIndex(index))
class SchemaDropper(DDLBase):
def __init__(
self, dialect, connection, checkfirst=False, tables=None, **kwargs
):
super(SchemaDropper, self).__init__(connection, **kwargs)
self.checkfirst = checkfirst
self.tables = tables
self.preparer = dialect.identifier_preparer
self.dialect = dialect
self.memo = {}
def visit_metadata(self, metadata):
if self.tables is not None:
tables = self.tables
else:
tables = list(metadata.tables.values())
try:
unsorted_tables = [t for t in tables if self._can_drop_table(t)]
collection = list(
reversed(
sort_tables_and_constraints(
unsorted_tables,
filter_fn=lambda constraint: False
if not self.dialect.supports_alter
or constraint.name is None
else None,
)
)
)
except exc.CircularDependencyError as err2:
if not self.dialect.supports_alter:
util.warn(
"Can't sort tables for DROP; an "
"unresolvable foreign key "
"dependency exists between tables: %s; and backend does "
"not support ALTER. To restore at least a partial sort, "
"apply use_alter=True to ForeignKey and "
"ForeignKeyConstraint "
"objects involved in the cycle to mark these as known "
"cycles that will be ignored."
% (", ".join(sorted([t.fullname for t in err2.cycles])))
)
collection = [(t, ()) for t in unsorted_tables]
else:
util.raise_(
exc.CircularDependencyError(
err2.args[0],
err2.cycles,
err2.edges,
msg="Can't sort tables for DROP; an "
"unresolvable foreign key "
"dependency exists between tables: %s. Please ensure "
"that the ForeignKey and ForeignKeyConstraint objects "
"involved in the cycle have "
"names so that they can be dropped using "
"DROP CONSTRAINT."
% (
", ".join(
sorted([t.fullname for t in err2.cycles])
)
),
),
from_=err2,
)
seq_coll = [
s
for s in metadata._sequences.values()
if self._can_drop_sequence(s)
]
event_collection = [t for (t, fks) in collection if t is not None]
metadata.dispatch.before_drop(
metadata,
self.connection,
tables=event_collection,
checkfirst=self.checkfirst,
_ddl_runner=self,
)
for table, fkcs in collection:
if table is not None:
self.traverse_single(
table,
drop_ok=True,
_is_metadata_operation=True,
_ignore_sequences=seq_coll,
)
else:
for fkc in fkcs:
self.traverse_single(fkc)
for seq in seq_coll:
self.traverse_single(seq, drop_ok=seq.column is None)
metadata.dispatch.after_drop(
metadata,
self.connection,
tables=event_collection,
checkfirst=self.checkfirst,
_ddl_runner=self,
)
def _can_drop_table(self, table):
self.dialect.validate_identifier(table.name)
effective_schema = self.connection.schema_for_object(table)
if effective_schema:
self.dialect.validate_identifier(effective_schema)
return not self.checkfirst or self.dialect.has_table(
self.connection, table.name, schema=effective_schema
)
def _can_drop_sequence(self, sequence):
effective_schema = self.connection.schema_for_object(sequence)
return self.dialect.supports_sequences and (
(not self.dialect.sequences_optional or not sequence.optional)
and (
not self.checkfirst
or self.dialect.has_sequence(
self.connection, sequence.name, schema=effective_schema
)
)
)
def visit_index(self, index):
self.connection.execute(DropIndex(index))
def visit_table(
self,
table,
drop_ok=False,
_is_metadata_operation=False,
_ignore_sequences=[],
):
if not drop_ok and not self._can_drop_table(table):
return
table.dispatch.before_drop(
table,
self.connection,
checkfirst=self.checkfirst,
_ddl_runner=self,
_is_metadata_operation=_is_metadata_operation,
)
self.connection.execute(DropTable(table))
# traverse client side defaults which may refer to server-side
# sequences. noting that some of these client side defaults may also be
# set up as server side defaults (see http://docs.sqlalchemy.org/en/
# latest/core/defaults.html#associating-a-sequence-as-the-server-side-
# default), so have to be dropped after the table is dropped.
for column in table.columns:
if (
column.default is not None
and column.default not in _ignore_sequences
):
self.traverse_single(column.default)
table.dispatch.after_drop(
table,
self.connection,
checkfirst=self.checkfirst,
_ddl_runner=self,
_is_metadata_operation=_is_metadata_operation,
)
def visit_foreign_key_constraint(self, constraint):
if not self.dialect.supports_alter:
return
self.connection.execute(DropConstraint(constraint))
def visit_sequence(self, sequence, drop_ok=False):
if not drop_ok and not self._can_drop_sequence(sequence):
return
self.connection.execute(DropSequence(sequence))
def sort_tables(
tables,
skip_fn=None,
extra_dependencies=None,
):
"""Sort a collection of :class:`_schema.Table` objects based on
dependency.
This is a dependency-ordered sort which will emit :class:`_schema.Table`
objects such that they will follow their dependent :class:`_schema.Table`
objects.
Tables are dependent on another based on the presence of
:class:`_schema.ForeignKeyConstraint`
objects as well as explicit dependencies
added by :meth:`_schema.Table.add_is_dependent_on`.
.. warning::
The :func:`._schema.sort_tables` function cannot by itself
accommodate automatic resolution of dependency cycles between
tables, which are usually caused by mutually dependent foreign key
constraints. When these cycles are detected, the foreign keys
of these tables are omitted from consideration in the sort.
A warning is emitted when this condition occurs, which will be an
exception raise in a future release. Tables which are not part
of the cycle will still be returned in dependency order.
To resolve these cycles, the
:paramref:`_schema.ForeignKeyConstraint.use_alter` parameter may be
applied to those constraints which create a cycle. Alternatively,
the :func:`_schema.sort_tables_and_constraints` function will
automatically return foreign key constraints in a separate
collection when cycles are detected so that they may be applied
to a schema separately.
.. versionchanged:: 1.3.17 - a warning is emitted when
:func:`_schema.sort_tables` cannot perform a proper sort due to
cyclical dependencies. This will be an exception in a future
release. Additionally, the sort will continue to return
other tables not involved in the cycle in dependency order
which was not the case previously.
:param tables: a sequence of :class:`_schema.Table` objects.
:param skip_fn: optional callable which will be passed a
:class:`_schema.ForeignKey` object; if it returns True, this
constraint will not be considered as a dependency. Note this is
**different** from the same parameter in
:func:`.sort_tables_and_constraints`, which is
instead passed the owning :class:`_schema.ForeignKeyConstraint` object.
:param extra_dependencies: a sequence of 2-tuples of tables which will
also be considered as dependent on each other.
.. seealso::
:func:`.sort_tables_and_constraints`
:attr:`_schema.MetaData.sorted_tables` - uses this function to sort
"""
if skip_fn is not None:
def _skip_fn(fkc):
for fk in fkc.elements:
if skip_fn(fk):
return True
else:
return None
else:
_skip_fn = None
return [
t
for (t, fkcs) in sort_tables_and_constraints(
tables,
filter_fn=_skip_fn,
extra_dependencies=extra_dependencies,
_warn_for_cycles=True,
)
if t is not None
]
def sort_tables_and_constraints(
tables, filter_fn=None, extra_dependencies=None, _warn_for_cycles=False
):
"""Sort a collection of :class:`_schema.Table` /
:class:`_schema.ForeignKeyConstraint`
objects.
This is a dependency-ordered sort which will emit tuples of
``(Table, [ForeignKeyConstraint, ...])`` such that each
:class:`_schema.Table` follows its dependent :class:`_schema.Table`
objects.
Remaining :class:`_schema.ForeignKeyConstraint`
objects that are separate due to
dependency rules not satisfied by the sort are emitted afterwards
as ``(None, [ForeignKeyConstraint ...])``.
Tables are dependent on another based on the presence of
:class:`_schema.ForeignKeyConstraint` objects, explicit dependencies
added by :meth:`_schema.Table.add_is_dependent_on`,
as well as dependencies
stated here using the :paramref:`~.sort_tables_and_constraints.skip_fn`
and/or :paramref:`~.sort_tables_and_constraints.extra_dependencies`
parameters.
:param tables: a sequence of :class:`_schema.Table` objects.
:param filter_fn: optional callable which will be passed a
:class:`_schema.ForeignKeyConstraint` object,
and returns a value based on
whether this constraint should definitely be included or excluded as
an inline constraint, or neither. If it returns False, the constraint
will definitely be included as a dependency that cannot be subject
to ALTER; if True, it will **only** be included as an ALTER result at
the end. Returning None means the constraint is included in the
table-based result unless it is detected as part of a dependency cycle.
:param extra_dependencies: a sequence of 2-tuples of tables which will
also be considered as dependent on each other.
.. versionadded:: 1.0.0
.. seealso::
:func:`.sort_tables`
"""
fixed_dependencies = set()
mutable_dependencies = set()
if extra_dependencies is not None:
fixed_dependencies.update(extra_dependencies)
remaining_fkcs = set()
for table in tables:
for fkc in table.foreign_key_constraints:
if fkc.use_alter is True:
remaining_fkcs.add(fkc)
continue
if filter_fn:
filtered = filter_fn(fkc)
if filtered is True:
remaining_fkcs.add(fkc)
continue
dependent_on = fkc.referred_table
if dependent_on is not table:
mutable_dependencies.add((dependent_on, table))
fixed_dependencies.update(
(parent, table) for parent in table._extra_dependencies
)
try:
candidate_sort = list(
topological.sort(
fixed_dependencies.union(mutable_dependencies),
tables,
deterministic_order=True,
)
)
except exc.CircularDependencyError as err:
if _warn_for_cycles:
util.warn(
"Cannot correctly sort tables; there are unresolvable cycles "
'between tables "%s", which is usually caused by mutually '
"dependent foreign key constraints. Foreign key constraints "
"involving these tables will not be considered; this warning "
"may raise an error in a future release."
% (", ".join(sorted(t.fullname for t in err.cycles)),)
)
for edge in err.edges:
if edge in mutable_dependencies:
table = edge[1]
if table not in err.cycles:
continue
can_remove = [
fkc
for fkc in table.foreign_key_constraints
if filter_fn is None or filter_fn(fkc) is not False
]
remaining_fkcs.update(can_remove)
for fkc in can_remove:
dependent_on = fkc.referred_table
if dependent_on is not table:
mutable_dependencies.discard((dependent_on, table))
candidate_sort = list(
topological.sort(
fixed_dependencies.union(mutable_dependencies),
tables,
deterministic_order=True,
)
)
return [
(table, table.foreign_key_constraints.difference(remaining_fkcs))
for table in candidate_sort
] + [(None, list(remaining_fkcs))]
|