- A large refactoring of the ``sqlalchemy.sql`` package has reorganized

the import structure of many core modules.
``sqlalchemy.schema`` and ``sqlalchemy.types``
remain in the top-level package, but are now just lists of names
that pull from within ``sqlalchemy.sql``.  Their implementations
are now broken out among ``sqlalchemy.sql.type_api``, ``sqlalchemy.sql.sqltypes``,
``sqlalchemy.sql.schema`` and ``sqlalchemy.sql.ddl``, the last of which was
moved from ``sqlalchemy.engine``.  ``sqlalchemy.sql.expression`` is also
a namespace now which pulls implementations mostly from ``sqlalchemy.sql.elements``,
``sqlalchemy.sql.selectable``, and ``sqlalchemy.sql.dml``.
Most of the "factory" functions
used to create SQL expression objects have been moved to classmethods
or constructors, which are exposed in ``sqlalchemy.sql.expression``
using a programmatic system.  Care has been taken such that all the
original import namespaces remain intact and there should be no impact
on any existing applications.   The rationale here was to break out these
very large modules into smaller ones, provide more manageable lists
of function names, to greatly reduce "import cycles" and clarify the
up-front importing of names, and to remove the need for redundant
functions and documentation throughout the expression package.

1 files changed, 826 insertions, 0 deletions

diff --git a/lib/sqlalchemy/sql/ddl.py b/lib/sqlalchemy/sql/ddl.py
new file mode 100644
index 000000000..ee13c07dd
--- /dev/null
+++ b/lib/sqlalchemy/sql/ddl.py
@@ -0,0 +1,826 @@
+# schema/ddl.py
+# Copyright (C) 2009-2013 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 .. import util
+from .elements import ClauseElement
+from .visitors import traverse
+from .base import Executable, _generative, SchemaVisitor, _bind_or_error
+from ..util import topological
+from .. import event
+from .. import exc
+
+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')
+        )
+
+    See also:
+
+        :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(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 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", "See :class:`.DDLEvents`, as well as "
+        ":meth:`.DDLElement.execute_if`.")
+    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:`.MetaData` and :class:`.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):
+        """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:`.Table` or :class:`.MetaData` object which is the
+              target of this event. May be None if the DDL is executed
+              explicitly.
+
+            :bind:
+              The :class:`.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.
+
+        See also:
+
+            :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:`.Table` or
+    :class:`.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 substitions 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
+    substutions noted above.  Keys present in the context will override
+    the standard substitutions.
+
+    """
+
+    __visit_name__ = "ddl"
+
+    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:
+          .. deprecated:: 0.7
+            See :meth:`.DDLElement.execute_if`.
+
+          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.
+
+
+        See also:
+
+            :class:`.DDLEvents`
+            :mod:`sqlalchemy.event`
+
+        """
+
+        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 constucts 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.
+
+    .. versionadded:: 0.7.4
+
+    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.
+
+    .. versionadded:: 0.7.4
+
+    """
+
+    __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):
+        """Create a :class:`.CreateTable` construct.
+
+        :param element: a :class:`.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`.
+
+        """
+        super(CreateTable, self).__init__(element, on=on, bind=bind)
+        self.columns = [CreateColumn(column)
+            for column in element.columns
+        ]
+
+
+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:`.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:`.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:`.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:`.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)
+        )
+
+    .. versionadded:: 0.8 The :class:`.CreateColumn` construct was added
+       to support custom column creation styles.
+
+    """
+    __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 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)
+        if table.schema:
+            self.dialect.validate_identifier(table.schema)
+        return not self.checkfirst or \
+                not self.dialect.has_table(self.connection,
+                                    table.name, schema=table.schema)
+
+    def _can_create_sequence(self, 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=sequence.schema)
+                     )
+            )
+
+    def visit_metadata(self, metadata):
+        if self.tables is not None:
+            tables = self.tables
+        else:
+            tables = list(metadata.tables.values())
+        collection = [t for t in sort_tables(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)]
+
+        metadata.dispatch.before_create(metadata, self.connection,
+                                    tables=collection,
+                                    checkfirst=self.checkfirst,
+                                            _ddl_runner=self)
+
+        for seq in seq_coll:
+            self.traverse_single(seq, create_ok=True)
+
+        for table in collection:
+            self.traverse_single(table, create_ok=True)
+
+        metadata.dispatch.after_create(metadata, self.connection,
+                                    tables=collection,
+                                    checkfirst=self.checkfirst,
+                                            _ddl_runner=self)
+
+    def visit_table(self, table, create_ok=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)
+
+        for column in table.columns:
+            if column.default is not None:
+                self.traverse_single(column.default)
+
+        self.connection.execute(CreateTable(table))
+
+        if hasattr(table, 'indexes'):
+            for index in table.indexes:
+                self.traverse_single(index)
+
+        table.dispatch.after_create(table, self.connection,
+                                        checkfirst=self.checkfirst,
+                                            _ddl_runner=self)
+
+    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())
+
+        collection = [
+            t
+            for t in reversed(sort_tables(tables))
+            if self._can_drop_table(t)
+        ]
+
+        seq_coll = [
+            s
+            for s in metadata._sequences.values()
+            if s.column is None and self._can_drop_sequence(s)
+        ]
+
+        metadata.dispatch.before_drop(
+            metadata, self.connection, tables=collection,
+            checkfirst=self.checkfirst, _ddl_runner=self)
+
+        for table in collection:
+            self.traverse_single(table, drop_ok=True)
+
+        for seq in seq_coll:
+            self.traverse_single(seq, drop_ok=True)
+
+        metadata.dispatch.after_drop(
+            metadata, self.connection, tables=collection,
+            checkfirst=self.checkfirst, _ddl_runner=self)
+
+    def _can_drop_table(self, table):
+        self.dialect.validate_identifier(table.name)
+        if table.schema:
+            self.dialect.validate_identifier(table.schema)
+        return not self.checkfirst or self.dialect.has_table(self.connection,
+                                            table.name, schema=table.schema)
+
+    def _can_drop_sequence(self, 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=sequence.schema))
+            )
+
+    def visit_index(self, index):
+        self.connection.execute(DropIndex(index))
+
+    def visit_table(self, table, drop_ok=False):
+        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)
+
+        for column in table.columns:
+            if column.default is not None:
+                self.traverse_single(column.default)
+
+        self.connection.execute(DropTable(table))
+
+        table.dispatch.after_drop(table, self.connection,
+                                        checkfirst=self.checkfirst,
+                                            _ddl_runner=self)
+
+    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 Table objects in order of
+                their foreign-key dependency."""
+
+    tables = list(tables)
+    tuples = []
+    if extra_dependencies is not None:
+        tuples.extend(extra_dependencies)
+
+    def visit_foreign_key(fkey):
+        if fkey.use_alter:
+            return
+        elif skip_fn and skip_fn(fkey):
+            return
+        parent_table = fkey.column.table
+        if parent_table in tables:
+            child_table = fkey.parent.table
+            if parent_table is not child_table:
+                tuples.append((parent_table, child_table))
+
+    for table in tables:
+        traverse(table,
+                            {'schema_visitor': True},
+                            {'foreign_key': visit_foreign_key})
+
+        tuples.extend(
+            [parent, table] for parent in table._extra_dependencies
+        )
+
+    return list(topological.sort(tuples, tables))
+