# engine/default.py
# Copyright (C) 2005-2014 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

"""Default implementations of per-dialect sqlalchemy.engine classes.

These are semi-private implementation classes which are only of importance
to database dialect authors; dialects will usually use the classes here
as the base class for their own corresponding classes.

"""

import re
import random
from . import reflection, interfaces, result
from ..sql import compiler, expression
from .. import types as sqltypes
from .. import exc, util, pool, processors
import codecs
import weakref
from .. import event

AUTOCOMMIT_REGEXP = re.compile(
            r'\s*(?:UPDATE|INSERT|CREATE|DELETE|DROP|ALTER)',
            re.I | re.UNICODE)



class DefaultDialect(interfaces.Dialect):
    """Default implementation of Dialect"""

    statement_compiler = compiler.SQLCompiler
    ddl_compiler = compiler.DDLCompiler
    type_compiler = compiler.GenericTypeCompiler
    preparer = compiler.IdentifierPreparer
    supports_alter = True

    # the first value we'd get for an autoincrement
    # column.
    default_sequence_base = 1

    # most DBAPIs happy with this for execute().
    # not cx_oracle.
    execute_sequence_format = tuple

    supports_views = True
    supports_sequences = False
    sequences_optional = False
    preexecute_autoincrement_sequences = False
    postfetch_lastrowid = True
    implicit_returning = False

    supports_right_nested_joins = True

    supports_native_enum = False
    supports_native_boolean = False

    supports_simple_order_by_label = True

    engine_config_types = util.immutabledict([
        ('convert_unicode', util.bool_or_str('force')),
        ('pool_timeout', int),
        ('echo', util.bool_or_str('debug')),
        ('echo_pool', util.bool_or_str('debug')),
        ('pool_recycle', int),
        ('pool_size', int),
        ('max_overflow', int),
        ('pool_threadlocal', bool),
        ('use_native_unicode', bool),
    ])

    # if the NUMERIC type
    # returns decimal.Decimal.
    # *not* the FLOAT type however.
    supports_native_decimal = False

    if util.py3k:
        supports_unicode_statements = True
        supports_unicode_binds = True
        returns_unicode_strings = True
        description_encoding = None
    else:
        supports_unicode_statements = False
        supports_unicode_binds = False
        returns_unicode_strings = False
        description_encoding = 'use_encoding'

    name = 'default'

    # length at which to truncate
    # any identifier.
    max_identifier_length = 9999

    # length at which to truncate
    # the name of an index.
    # Usually None to indicate
    # 'use max_identifier_length'.
    # thanks to MySQL, sigh
    max_index_name_length = None

    supports_sane_rowcount = True
    supports_sane_multi_rowcount = True
    dbapi_type_map = {}
    colspecs = {}
    default_paramstyle = 'named'
    supports_default_values = False
    supports_empty_insert = True
    supports_multivalues_insert = False

    server_version_info = None

    construct_arguments = None
    """Optional set of argument specifiers for various SQLAlchemy
    constructs, typically schema items.

    To implement, establish as a series of tuples, as in::

        construct_arguments = [
            (schema.Index, {
                "using": False,
                "where": None,
                "ops": None
            })
        ]

    If the above construct is established on the Postgresql dialect,
    the :class:`.Index` construct will now accept the keyword arguments
    ``postgresql_using``, ``postgresql_where``, nad ``postgresql_ops``.
    Any other argument specified to the constructor of :class:`.Index`
    which is prefixed with ``postgresql_`` will raise :class:`.ArgumentError`.

    A dialect which does not include a ``construct_arguments`` member will
    not participate in the argument validation system.  For such a dialect,
    any argument name is accepted by all participating constructs, within
    the namespace of arguments prefixed with that dialect name.  The rationale
    here is so that third-party dialects that haven't yet implemented this
    feature continue to function in the old way.

    .. versionadded:: 0.9.2

    .. seealso::

        :class:`.DialectKWArgs` - implementing base class which consumes
        :attr:`.DefaultDialect.construct_arguments`


    """

    # indicates symbol names are
    # UPPERCASEd if they are case insensitive
    # within the database.
    # if this is True, the methods normalize_name()
    # and denormalize_name() must be provided.
    requires_name_normalize = False

    reflection_options = ()

    def __init__(self, convert_unicode=False,
                 encoding='utf-8', paramstyle=None, dbapi=None,
                 implicit_returning=None,
                 supports_right_nested_joins=None,
                 case_sensitive=True,
                 supports_native_boolean=None,
                 label_length=None, **kwargs):

        if not getattr(self, 'ported_sqla_06', True):
            util.warn(
                "The %s dialect is not yet ported to the 0.6 format" %
                self.name)

        self.convert_unicode = convert_unicode
        self.encoding = encoding
        self.positional = False
        self._ischema = None
        self.dbapi = dbapi
        if paramstyle is not None:
            self.paramstyle = paramstyle
        elif self.dbapi is not None:
            self.paramstyle = self.dbapi.paramstyle
        else:
            self.paramstyle = self.default_paramstyle
        if implicit_returning is not None:
            self.implicit_returning = implicit_returning
        self.positional = self.paramstyle in ('qmark', 'format', 'numeric')
        self.identifier_preparer = self.preparer(self)
        self.type_compiler = self.type_compiler(self)
        if supports_right_nested_joins is not None:
            self.supports_right_nested_joins = supports_right_nested_joins
        if supports_native_boolean is not None:
            self.supports_native_boolean = supports_native_boolean
        self.case_sensitive = case_sensitive

        if label_length and label_length > self.max_identifier_length:
            raise exc.ArgumentError(
                    "Label length of %d is greater than this dialect's"
                    " maximum identifier length of %d" %
                    (label_length, self.max_identifier_length))
        self.label_length = label_length

        if self.description_encoding == 'use_encoding':
            self._description_decoder = \
                            processors.to_unicode_processor_factory(
                                            encoding
                                    )
        elif self.description_encoding is not None:
            self._description_decoder = \
                            processors.to_unicode_processor_factory(
                                            self.description_encoding
                                    )
        self._encoder = codecs.getencoder(self.encoding)
        self._decoder = processors.to_unicode_processor_factory(self.encoding)



    @util.memoized_property
    def _type_memos(self):
        return weakref.WeakKeyDictionary()

    @property
    def dialect_description(self):
        return self.name + "+" + self.driver

    @classmethod
    def get_pool_class(cls, url):
        return getattr(cls, 'poolclass', pool.QueuePool)

    def initialize(self, connection):
        try:
            self.server_version_info = \
                            self._get_server_version_info(connection)
        except NotImplementedError:
            self.server_version_info = None
        try:
            self.default_schema_name = \
                            self._get_default_schema_name(connection)
        except NotImplementedError:
            self.default_schema_name = None

        try:
            self.default_isolation_level = \
                        self.get_isolation_level(connection.connection)
        except NotImplementedError:
            self.default_isolation_level = None

        self.returns_unicode_strings = self._check_unicode_returns(connection)

        if self.description_encoding is not None and \
            self._check_unicode_description(connection):
            self._description_decoder = self.description_encoding = None

        self.do_rollback(connection.connection)

    def on_connect(self):
        """return a callable which sets up a newly created DBAPI connection.

        This is used to set dialect-wide per-connection options such as
        isolation modes, unicode modes, etc.

        If a callable is returned, it will be assembled into a pool listener
        that receives the direct DBAPI connection, with all wrappers removed.

        If None is returned, no listener will be generated.

        """
        return None

    def _check_unicode_returns(self, connection, additional_tests=None):
        if util.py2k and not self.supports_unicode_statements:
            cast_to = util.binary_type
        else:
            cast_to = util.text_type

        if self.positional:
            parameters = self.execute_sequence_format()
        else:
            parameters = {}

        def check_unicode(test):
            statement = cast_to(expression.select([test]).compile(dialect=self))
            try:
                cursor = connection.connection.cursor()
                connection._cursor_execute(cursor, statement, parameters)
                row = cursor.fetchone()
                cursor.close()
            except exc.DBAPIError as de:
                # note that _cursor_execute() will have closed the cursor
                # if an exception is thrown.
                util.warn("Exception attempting to "
                        "detect unicode returns: %r" % de)
                return False
            else:
                return isinstance(row[0], util.text_type)

        tests = [
            # detect plain VARCHAR
            expression.cast(
                expression.literal_column("'test plain returns'"),
                sqltypes.VARCHAR(60)
            ),
            # detect if there's an NVARCHAR type with different behavior available
            expression.cast(
                expression.literal_column("'test unicode returns'"),
                sqltypes.Unicode(60)
            ),
        ]

        if additional_tests:
            tests += additional_tests

        results = set([check_unicode(test) for test in tests])

        if results.issuperset([True, False]):
            return "conditional"
        else:
            return results == set([True])

    def _check_unicode_description(self, connection):
        # all DBAPIs on Py2K return cursor.description as encoded,
        # until pypy2.1beta2 with sqlite, so let's just check it -
        # it's likely others will start doing this too in Py2k.

        if util.py2k and not self.supports_unicode_statements:
            cast_to = util.binary_type
        else:
            cast_to = util.text_type

        cursor = connection.connection.cursor()
        try:
            cursor.execute(
                cast_to(
                    expression.select([
                        expression.literal_column("'x'").label("some_label")
                    ]).compile(dialect=self)
                )
            )
            return isinstance(cursor.description[0][0], util.text_type)
        finally:
            cursor.close()

    def type_descriptor(self, typeobj):
        """Provide a database-specific :class:`.TypeEngine` object, given
        the generic object which comes from the types module.

        This method looks for a dictionary called
        ``colspecs`` as a class or instance-level variable,
        and passes on to :func:`.types.adapt_type`.

        """
        return sqltypes.adapt_type(typeobj, self.colspecs)

    def reflecttable(self, connection, table, include_columns, exclude_columns):
        insp = reflection.Inspector.from_engine(connection)
        return insp.reflecttable(table, include_columns, exclude_columns)

    def get_pk_constraint(self, conn, table_name, schema=None, **kw):
        """Compatibility method, adapts the result of get_primary_keys()
        for those dialects which don't implement get_pk_constraint().

        """
        return {
            'constrained_columns':
                        self.get_primary_keys(conn, table_name,
                                                schema=schema, **kw)
        }

    def validate_identifier(self, ident):
        if len(ident) > self.max_identifier_length:
            raise exc.IdentifierError(
                "Identifier '%s' exceeds maximum length of %d characters" %
                (ident, self.max_identifier_length)
            )

    def connect(self, *cargs, **cparams):
        return self.dbapi.connect(*cargs, **cparams)

    def create_connect_args(self, url):
        opts = url.translate_connect_args()
        opts.update(url.query)
        return [[], opts]

    def set_engine_execution_options(self, engine, opts):
        if 'isolation_level' in opts:
            isolation_level = opts['isolation_level']
            @event.listens_for(engine, "engine_connect")
            def set_isolation(connection, branch):
                if not branch:
                    self._set_connection_isolation(connection, isolation_level)

    def set_connection_execution_options(self, connection, opts):
        if 'isolation_level' in opts:
            self._set_connection_isolation(connection, opts['isolation_level'])

    def _set_connection_isolation(self, connection, level):
        self.set_isolation_level(connection.connection, level)
        connection.connection._connection_record.\
            finalize_callback.append(self.reset_isolation_level)


    def do_begin(self, dbapi_connection):
        pass

    def do_rollback(self, dbapi_connection):
        dbapi_connection.rollback()

    def do_commit(self, dbapi_connection):
        dbapi_connection.commit()

    def do_close(self, dbapi_connection):
        dbapi_connection.close()

    def create_xid(self):
        """Create a random two-phase transaction ID.

        This id will be passed to do_begin_twophase(), do_rollback_twophase(),
        do_commit_twophase().  Its format is unspecified.
        """

        return "_sa_%032x" % random.randint(0, 2 ** 128)

    def do_savepoint(self, connection, name):
        connection.execute(expression.SavepointClause(name))

    def do_rollback_to_savepoint(self, connection, name):
        connection.execute(expression.RollbackToSavepointClause(name))

    def do_release_savepoint(self, connection, name):
        connection.execute(expression.ReleaseSavepointClause(name))

    def do_executemany(self, cursor, statement, parameters, context=None):
        cursor.executemany(statement, parameters)

    def do_execute(self, cursor, statement, parameters, context=None):
        cursor.execute(statement, parameters)

    def do_execute_no_params(self, cursor, statement, context=None):
        cursor.execute(statement)

    def is_disconnect(self, e, connection, cursor):
        return False

    def reset_isolation_level(self, dbapi_conn):
        # default_isolation_level is read from the first connection
        # after the initial set of 'isolation_level', if any, so is
        # the configured default of this dialect.
        self.set_isolation_level(dbapi_conn, self.default_isolation_level)


class DefaultExecutionContext(interfaces.ExecutionContext):
    isinsert = False
    isupdate = False
    isdelete = False
    isddl = False
    executemany = False
    result_map = None
    compiled = None
    statement = None
    postfetch_cols = None
    prefetch_cols = None
    returning_cols = None
    _is_implicit_returning = False
    _is_explicit_returning = False

    # a hook for SQLite's translation of
    # result column names
    _translate_colname = None

    @classmethod
    def _init_ddl(cls, dialect, connection, dbapi_connection, compiled_ddl):
        """Initialize execution context for a DDLElement construct."""

        self = cls.__new__(cls)
        self.dialect = dialect
        self.root_connection = connection
        self._dbapi_connection = dbapi_connection
        self.engine = connection.engine

        self.compiled = compiled = compiled_ddl
        self.isddl = True

        self.execution_options = compiled.statement._execution_options
        if connection._execution_options:
            self.execution_options = dict(self.execution_options)
            self.execution_options.update(connection._execution_options)

        if not dialect.supports_unicode_statements:
            self.unicode_statement = util.text_type(compiled)
            self.statement = dialect._encoder(self.unicode_statement)[0]
        else:
            self.statement = self.unicode_statement = util.text_type(compiled)

        self.cursor = self.create_cursor()
        self.compiled_parameters = []

        if dialect.positional:
            self.parameters = [dialect.execute_sequence_format()]
        else:
            self.parameters = [{}]

        return self

    @classmethod
    def _init_compiled(cls, dialect, connection, dbapi_connection,
                    compiled, parameters):
        """Initialize execution context for a Compiled construct."""

        self = cls.__new__(cls)
        self.dialect = dialect
        self.root_connection = connection
        self._dbapi_connection = dbapi_connection
        self.engine = connection.engine

        self.compiled = compiled

        if not compiled.can_execute:
            raise exc.ArgumentError("Not an executable clause")

        self.execution_options = compiled.statement._execution_options
        if connection._execution_options:
            self.execution_options = dict(self.execution_options)
            self.execution_options.update(connection._execution_options)

        # compiled clauseelement.  process bind params, process table defaults,
        # track collections used by ResultProxy to target and process results

        self.result_map = compiled.result_map

        self.unicode_statement = util.text_type(compiled)
        if not dialect.supports_unicode_statements:
            self.statement = self.unicode_statement.encode(
                                        self.dialect.encoding)
        else:
            self.statement = self.unicode_statement

        self.isinsert = compiled.isinsert
        self.isupdate = compiled.isupdate
        self.isdelete = compiled.isdelete

        if self.isinsert or self.isupdate or self.isdelete:
            self._is_explicit_returning = bool(compiled.statement._returning)
            self._is_implicit_returning = bool(compiled.returning and \
                                            not compiled.statement._returning)

        if not parameters:
            self.compiled_parameters = [compiled.construct_params()]
        else:
            self.compiled_parameters = \
                        [compiled.construct_params(m, _group_number=grp) for
                                        grp, m in enumerate(parameters)]

            self.executemany = len(parameters) > 1

        self.cursor = self.create_cursor()
        if self.isinsert or self.isupdate:
            self.postfetch_cols = self.compiled.postfetch
            self.prefetch_cols = self.compiled.prefetch
            self.returning_cols = self.compiled.returning
            self.__process_defaults()

        processors = compiled._bind_processors

        # Convert the dictionary of bind parameter values
        # into a dict or list to be sent to the DBAPI's
        # execute() or executemany() method.
        parameters = []
        if dialect.positional:
            for compiled_params in self.compiled_parameters:
                param = []
                for key in self.compiled.positiontup:
                    if key in processors:
                        param.append(processors[key](compiled_params[key]))
                    else:
                        param.append(compiled_params[key])
                parameters.append(dialect.execute_sequence_format(param))
        else:
            encode = not dialect.supports_unicode_statements
            for compiled_params in self.compiled_parameters:
                param = {}
                if encode:
                    for key in compiled_params:
                        if key in processors:
                            param[dialect._encoder(key)[0]] = \
                                        processors[key](compiled_params[key])
                        else:
                            param[dialect._encoder(key)[0]] = \
                                    compiled_params[key]
                else:
                    for key in compiled_params:
                        if key in processors:
                            param[key] = processors[key](compiled_params[key])
                        else:
                            param[key] = compiled_params[key]
                parameters.append(param)
        self.parameters = dialect.execute_sequence_format(parameters)

        return self

    @classmethod
    def _init_statement(cls, dialect, connection, dbapi_connection,
                                                    statement, parameters):
        """Initialize execution context for a string SQL statement."""

        self = cls.__new__(cls)
        self.dialect = dialect
        self.root_connection = connection
        self._dbapi_connection = dbapi_connection
        self.engine = connection.engine

        # plain text statement
        self.execution_options = connection._execution_options

        if not parameters:
            if self.dialect.positional:
                self.parameters = [dialect.execute_sequence_format()]
            else:
                self.parameters = [{}]
        elif isinstance(parameters[0], dialect.execute_sequence_format):
            self.parameters = parameters
        elif isinstance(parameters[0], dict):
            if dialect.supports_unicode_statements:
                self.parameters = parameters
            else:
                self.parameters = [
                            dict((dialect._encoder(k)[0], d[k]) for k in d)
                            for d in parameters
                        ] or [{}]
        else:
            self.parameters = [dialect.execute_sequence_format(p)
                                    for p in parameters]

        self.executemany = len(parameters) > 1

        if not dialect.supports_unicode_statements and \
                isinstance(statement, util.text_type):
            self.unicode_statement = statement
            self.statement = dialect._encoder(statement)[0]
        else:
            self.statement = self.unicode_statement = statement

        self.cursor = self.create_cursor()
        return self

    @classmethod
    def _init_default(cls, dialect, connection, dbapi_connection):
        """Initialize execution context for a ColumnDefault construct."""

        self = cls.__new__(cls)
        self.dialect = dialect
        self.root_connection = connection
        self._dbapi_connection = dbapi_connection
        self.engine = connection.engine
        self.execution_options = connection._execution_options
        self.cursor = self.create_cursor()
        return self

    @util.memoized_property
    def no_parameters(self):
        return self.execution_options.get("no_parameters", False)

    @util.memoized_property
    def is_crud(self):
        return self.isinsert or self.isupdate or self.isdelete

    @util.memoized_property
    def should_autocommit(self):
        autocommit = self.execution_options.get('autocommit',
                                                not self.compiled and
                                                self.statement and
                                                expression.PARSE_AUTOCOMMIT
                                                or False)

        if autocommit is expression.PARSE_AUTOCOMMIT:
            return self.should_autocommit_text(self.unicode_statement)
        else:
            return autocommit

    def _execute_scalar(self, stmt, type_):
        """Execute a string statement on the current cursor, returning a
        scalar result.

        Used to fire off sequences, default phrases, and "select lastrowid"
        types of statements individually or in the context of a parent INSERT
        or UPDATE statement.

        """

        conn = self.root_connection
        if isinstance(stmt, util.text_type) and \
                not self.dialect.supports_unicode_statements:
            stmt = self.dialect._encoder(stmt)[0]

        if self.dialect.positional:
            default_params = self.dialect.execute_sequence_format()
        else:
            default_params = {}

        conn._cursor_execute(self.cursor, stmt, default_params, context=self)
        r = self.cursor.fetchone()[0]
        if type_ is not None:
            # apply type post processors to the result
            proc = type_._cached_result_processor(
                        self.dialect,
                        self.cursor.description[0][1]
                    )
            if proc:
                return proc(r)
        return r

    @property
    def connection(self):
        return self.root_connection._branch()

    def should_autocommit_text(self, statement):
        return AUTOCOMMIT_REGEXP.match(statement)

    def create_cursor(self):
        return self._dbapi_connection.cursor()

    def pre_exec(self):
        pass

    def post_exec(self):
        pass

    def get_result_processor(self, type_, colname, coltype):
        """Return a 'result processor' for a given type as present in
        cursor.description.

        This has a default implementation that dialects can override
        for context-sensitive result type handling.

        """
        return type_._cached_result_processor(self.dialect, coltype)

    def get_lastrowid(self):
        """return self.cursor.lastrowid, or equivalent, after an INSERT.

        This may involve calling special cursor functions,
        issuing a new SELECT on the cursor (or a new one),
        or returning a stored value that was
        calculated within post_exec().

        This function will only be called for dialects
        which support "implicit" primary key generation,
        keep preexecute_autoincrement_sequences set to False,
        and when no explicit id value was bound to the
        statement.

        The function is called once, directly after
        post_exec() and before the transaction is committed
        or ResultProxy is generated.   If the post_exec()
        method assigns a value to `self._lastrowid`, the
        value is used in place of calling get_lastrowid().

        Note that this method is *not* equivalent to the
        ``lastrowid`` method on ``ResultProxy``, which is a
        direct proxy to the DBAPI ``lastrowid`` accessor
        in all cases.

        """
        return self.cursor.lastrowid

    def handle_dbapi_exception(self, e):
        pass

    def get_result_proxy(self):
        return result.ResultProxy(self)

    @property
    def rowcount(self):
        return self.cursor.rowcount

    def supports_sane_rowcount(self):
        return self.dialect.supports_sane_rowcount

    def supports_sane_multi_rowcount(self):
        return self.dialect.supports_sane_multi_rowcount

    def post_insert(self):
        if not self._is_implicit_returning and \
            not self._is_explicit_returning and \
            not self.compiled.inline and \
            self.dialect.postfetch_lastrowid and \
            (not self.inserted_primary_key or \
                        None in self.inserted_primary_key):

            table = self.compiled.statement.table
            lastrowid = self.get_lastrowid()
            autoinc_col = table._autoincrement_column
            if autoinc_col is not None:
                # apply type post processors to the lastrowid
                proc = autoinc_col.type._cached_result_processor(
                                        self.dialect, None)
                if proc is not None:
                    lastrowid = proc(lastrowid)

            self.inserted_primary_key = [
                lastrowid if c is autoinc_col else v
                for c, v in zip(
                                    table.primary_key,
                                    self.inserted_primary_key)
            ]

    def _fetch_implicit_returning(self, resultproxy):
        table = self.compiled.statement.table
        row = resultproxy.fetchone()

        ipk = []
        for c, v in zip(table.primary_key, self.inserted_primary_key):
            if v is not None:
                ipk.append(v)
            else:
                ipk.append(row[c])

        self.inserted_primary_key = ipk
        self.returned_defaults = row

    def _fetch_implicit_update_returning(self, resultproxy):
        row = resultproxy.fetchone()
        self.returned_defaults = row

    def lastrow_has_defaults(self):
        return (self.isinsert or self.isupdate) and \
            bool(self.postfetch_cols)

    def set_input_sizes(self, translate=None, exclude_types=None):
        """Given a cursor and ClauseParameters, call the appropriate
        style of ``setinputsizes()`` on the cursor, using DB-API types
        from the bind parameter's ``TypeEngine`` objects.

        This method only called by those dialects which require it,
        currently cx_oracle.

        """

        if not hasattr(self.compiled, 'bind_names'):
            return

        types = dict(
                (self.compiled.bind_names[bindparam], bindparam.type)
                 for bindparam in self.compiled.bind_names)

        if self.dialect.positional:
            inputsizes = []
            for key in self.compiled.positiontup:
                typeengine = types[key]
                dbtype = typeengine.dialect_impl(self.dialect).\
                                    get_dbapi_type(self.dialect.dbapi)
                if dbtype is not None and \
                    (not exclude_types or dbtype not in exclude_types):
                    inputsizes.append(dbtype)
            try:
                self.cursor.setinputsizes(*inputsizes)
            except Exception as e:
                self.root_connection._handle_dbapi_exception(
                                e, None, None, None, self)
        else:
            inputsizes = {}
            for key in self.compiled.bind_names.values():
                typeengine = types[key]
                dbtype = typeengine.dialect_impl(self.dialect).\
                                get_dbapi_type(self.dialect.dbapi)
                if dbtype is not None and \
                        (not exclude_types or dbtype not in exclude_types):
                    if translate:
                        key = translate.get(key, key)
                    if not self.dialect.supports_unicode_binds:
                        key = self.dialect._encoder(key)[0]
                    inputsizes[key] = dbtype
            try:
                self.cursor.setinputsizes(**inputsizes)
            except Exception as e:
                self.root_connection._handle_dbapi_exception(
                                e, None, None, None, self)

    def _exec_default(self, default, type_):
        if default.is_sequence:
            return self.fire_sequence(default, type_)
        elif default.is_callable:
            return default.arg(self)
        elif default.is_clause_element:
            # TODO: expensive branching here should be
            # pulled into _exec_scalar()
            conn = self.connection
            c = expression.select([default.arg]).compile(bind=conn)
            return conn._execute_compiled(c, (), {}).scalar()
        else:
            return default.arg

    def get_insert_default(self, column):
        if column.default is None:
            return None
        else:
            return self._exec_default(column.default, column.type)

    def get_update_default(self, column):
        if column.onupdate is None:
            return None
        else:
            return self._exec_default(column.onupdate, column.type)

    def __process_defaults(self):
        """Generate default values for compiled insert/update statements,
        and generate inserted_primary_key collection.
        """

        key_getter = self.compiled._key_getters_for_crud_column[2]

        if self.executemany:
            if len(self.compiled.prefetch):
                scalar_defaults = {}

                # pre-determine scalar Python-side defaults
                # to avoid many calls of get_insert_default()/
                # get_update_default()
                for c in self.prefetch_cols:
                    if self.isinsert and c.default and c.default.is_scalar:
                        scalar_defaults[c] = c.default.arg
                    elif self.isupdate and c.onupdate and c.onupdate.is_scalar:
                        scalar_defaults[c] = c.onupdate.arg

                for param in self.compiled_parameters:
                    self.current_parameters = param
                    for c in self.prefetch_cols:
                        if c in scalar_defaults:
                            val = scalar_defaults[c]
                        elif self.isinsert:
                            val = self.get_insert_default(c)
                        else:
                            val = self.get_update_default(c)
                        if val is not None:
                            param[key_getter(c)] = val
                del self.current_parameters
        else:
            self.current_parameters = compiled_parameters = \
                                        self.compiled_parameters[0]

            for c in self.compiled.prefetch:
                if self.isinsert:
                    val = self.get_insert_default(c)
                else:
                    val = self.get_update_default(c)

                if val is not None:
                    compiled_parameters[key_getter(c)] = val
            del self.current_parameters

            if self.isinsert:
                self.inserted_primary_key = [
                                self.compiled_parameters[0].get(key_getter(c), None)
                                        for c in self.compiled.\
                                                statement.table.primary_key
                                ]


DefaultDialect.execution_ctx_cls = DefaultExecutionContext
