SickGear/lib/sqlalchemy/dialects/sqlite/base.py

# sqlite/base.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

"""
.. dialect:: sqlite
    :name: SQLite


Date and Time Types
-------------------

SQLite does not have built-in DATE, TIME, or DATETIME types, and pysqlite does
not provide out of the box functionality for translating values between Python
`datetime` objects and a SQLite-supported format. SQLAlchemy's own
:class:`~sqlalchemy.types.DateTime` and related types provide date formatting
and parsing functionality when SQlite is used. The implementation classes are
:class:`~.sqlite.DATETIME`, :class:`~.sqlite.DATE` and :class:`~.sqlite.TIME`.
These types represent dates and times as ISO formatted strings, which also
nicely support ordering. There's no reliance on typical "libc" internals for
these functions so historical dates are fully supported.

Auto Incrementing Behavior
--------------------------

Background on SQLite's autoincrement is at: http://sqlite.org/autoinc.html

Two things to note:

* The AUTOINCREMENT keyword is **not** required for SQLite tables to
  generate primary key values automatically. AUTOINCREMENT only means that the
  algorithm used to generate ROWID values should be slightly different.
* SQLite does **not** generate primary key (i.e. ROWID) values, even for
  one column, if the table has a composite (i.e. multi-column) primary key.
  This is regardless of the AUTOINCREMENT keyword being present or not.

To specifically render the AUTOINCREMENT keyword on the primary key column when
rendering DDL, add the flag ``sqlite_autoincrement=True`` to the Table
construct::

    Table('sometable', metadata,
            Column('id', Integer, primary_key=True),
            sqlite_autoincrement=True)

Transaction Isolation Level
---------------------------

:func:`.create_engine` accepts an ``isolation_level`` parameter which results
in the command ``PRAGMA read_uncommitted <level>`` being invoked for every new
connection. Valid values for this parameter are ``SERIALIZABLE`` and ``READ
UNCOMMITTED`` corresponding to a value of 0 and 1, respectively. See the
section :ref:`pysqlite_serializable` for an important workaround when using
serializable isolation with Pysqlite.

Database Locking Behavior / Concurrency
---------------------------------------

Note that SQLite is not designed for a high level of concurrency. The database
itself, being a file, is locked completely during write operations and within
transactions, meaning exactly one connection has exclusive access to the
database during this period - all other connections will be blocked during this
time.

The Python DBAPI specification also calls for a connection model that is always
in a transaction; there is no BEGIN method, only commit and rollback. This
implies that a SQLite DBAPI driver would technically allow only serialized
access to a particular database file at all times. The pysqlite driver attempts
to ameliorate this by deferring the actual BEGIN statement until the first DML
(INSERT, UPDATE, or DELETE) is received within a transaction. While this breaks
serializable isolation, it at least delays the exclusive locking inherent in
SQLite's design.

SQLAlchemy's default mode of usage with the ORM is known as "autocommit=False",
which means the moment the :class:`.Session` begins to be used, a transaction
is begun. As the :class:`.Session` is used, the autoflush feature, also on by
default, will flush out pending changes to the database before each query. The
effect of this is that a :class:`.Session` used in its default mode will often
emit DML early on, long before the transaction is actually committed. This
again will have the effect of serializing access to the SQLite database. If
highly concurrent reads are desired against the SQLite database, it is advised
that the autoflush feature be disabled, and potentially even that autocommit be
re-enabled, which has the effect of each SQL statement and flush committing
changes immediately.

For more information on SQLite's lack of concurrency by design, please see
`Situations Where Another RDBMS May Work Better - High Concurrency
<http://www.sqlite.org/whentouse.html>`_ near the bottom of the page.

.. _sqlite_foreign_keys:

Foreign Key Support
-------------------

SQLite supports FOREIGN KEY syntax when emitting CREATE statements for tables,
however by default these constraints have no effect on the operation of the
table.

Constraint checking on SQLite has three prerequisites:

* At least version 3.6.19 of SQLite must be in use
* The SQLite library must be compiled *without* the SQLITE_OMIT_FOREIGN_KEY
  or SQLITE_OMIT_TRIGGER symbols enabled.
* The ``PRAGMA foreign_keys = ON`` statement must be emitted on all connections
  before use.

SQLAlchemy allows for the ``PRAGMA`` statement to be emitted automatically for
new connections through the usage of events::

    from sqlalchemy.engine import Engine
    from sqlalchemy import event

    @event.listens_for(Engine, "connect")
    def set_sqlite_pragma(dbapi_connection, connection_record):
        cursor = dbapi_connection.cursor()
        cursor.execute("PRAGMA foreign_keys=ON")
        cursor.close()

.. seealso::

    `SQLite Foreign Key Support <http://www.sqlite.org/foreignkeys.html>`_ - on
    the SQLite web site.

    :ref:`event_toplevel` - SQLAlchemy event API.

.. _sqlite_type_reflection:

Type Reflection
---------------

SQLite types are unlike those of most other database backends, in that
the string name of the type usually does not correspond to a "type" in a
one-to-one fashion.  Instead, SQLite links per-column typing behavior
to one of five so-called "type affinities" based on a string matching
pattern for the type.

SQLAlchemy's reflection process, when inspecting types, uses a simple
lookup table to link the keywords returned to provided SQLAlchemy types.
This lookup table is present within the SQLite dialect as it is for all
other dialects.  However, the SQLite dialect has a different "fallback"
routine for when a particular type name is not located in the lookup map;
it instead implements the SQLite "type affinity" scheme located at
http://www.sqlite.org/datatype3.html section 2.1.

The provided typemap will make direct associations from an exact string
name match for the following types:

:class:`~.types.BIGINT`, :class:`~.types.BLOB`,
:class:`~.types.BOOLEAN`, :class:`~.types.BOOLEAN`,
:class:`~.types.CHAR`, :class:`~.types.DATE`,
:class:`~.types.DATETIME`, :class:`~.types.FLOAT`,
:class:`~.types.DECIMAL`, :class:`~.types.FLOAT`,
:class:`~.types.INTEGER`, :class:`~.types.INTEGER`,
:class:`~.types.NUMERIC`, :class:`~.types.REAL`,
:class:`~.types.SMALLINT`, :class:`~.types.TEXT`,
:class:`~.types.TIME`, :class:`~.types.TIMESTAMP`,
:class:`~.types.VARCHAR`, :class:`~.types.NVARCHAR`,
:class:`~.types.NCHAR`

When a type name does not match one of the above types, the "type affinity"
lookup is used instead:

* :class:`~.types.INTEGER` is returned if the type name includes the
  string ``INT``
* :class:`~.types.TEXT` is returned if the type name includes the
  string ``CHAR``, ``CLOB`` or ``TEXT``
* :class:`~.types.NullType` is returned if the type name includes the
  string ``BLOB``
* :class:`~.types.REAL` is returned if the type name includes the string
  ``REAL``, ``FLOA`` or ``DOUB``.
* Otherwise, the :class:`~.types.NUMERIC` type is used.

.. versionadded:: 0.9.3 Support for SQLite type affinity rules when reflecting
   columns.

"""

import datetime
import re

from ... import processors
from ... import sql, exc
from ... import types as sqltypes, schema as sa_schema
from ... import util
from ...engine import default, reflection
from ...sql import compiler

from ...types import (BLOB, BOOLEAN, CHAR, DATE, DECIMAL, FLOAT, INTEGER, REAL,
                      NUMERIC, SMALLINT, TEXT, TIMESTAMP, VARCHAR)


class _DateTimeMixin(object):
    _reg = None
    _storage_format = None

    def __init__(self, storage_format=None, regexp=None, **kw):
        super(_DateTimeMixin, self).__init__(**kw)
        if regexp is not None:
            self._reg = re.compile(regexp)
        if storage_format is not None:
            self._storage_format = storage_format

    def adapt(self, cls, **kw):
        if issubclass(cls, _DateTimeMixin):
            if self._storage_format:
                kw["storage_format"] = self._storage_format
            if self._reg:
                kw["regexp"] = self._reg
        return super(_DateTimeMixin, self).adapt(cls, **kw)

    def literal_processor(self, dialect):
        bp = self.bind_processor(dialect)
        def process(value):
            return "'%s'" % bp(value)
        return process


class DATETIME(_DateTimeMixin, sqltypes.DateTime):
    """Represent a Python datetime object in SQLite using a string.

    The default string storage format is::

        "%(year)04d-%(month)02d-%(day)02d %(hour)02d:%(min)02d:%(second)02d.%(microsecond)06d"

    e.g.::

        2011-03-15 12:05:57.10558

    The storage format can be customized to some degree using the
    ``storage_format`` and ``regexp`` parameters, such as::

        import re
        from sqlalchemy.dialects.sqlite import DATETIME

        dt = DATETIME(
            storage_format="%(year)04d/%(month)02d/%(day)02d %(hour)02d:%(min)02d:%(second)02d",
            regexp=r"(\d+)/(\d+)/(\d+) (\d+)-(\d+)-(\d+)"
        )

    :param storage_format: format string which will be applied to the dict with
     keys year, month, day, hour, minute, second, and microsecond.

    :param regexp: regular expression which will be applied to incoming result
     rows. If the regexp contains named groups, the resulting match dict is
     applied to the Python datetime() constructor as keyword arguments.
     Otherwise, if positional groups are used, the datetime() constructor
     is called with positional arguments via
     ``*map(int, match_obj.groups(0))``.
    """

    _storage_format = (
        "%(year)04d-%(month)02d-%(day)02d "
        "%(hour)02d:%(minute)02d:%(second)02d.%(microsecond)06d"
    )

    def __init__(self, *args, **kwargs):
        truncate_microseconds = kwargs.pop('truncate_microseconds', False)
        super(DATETIME, self).__init__(*args, **kwargs)
        if truncate_microseconds:
            assert 'storage_format' not in kwargs, "You can specify only "\
                "one of truncate_microseconds or storage_format."
            assert 'regexp' not in kwargs, "You can specify only one of "\
                "truncate_microseconds or regexp."
            self._storage_format = (
                "%(year)04d-%(month)02d-%(day)02d "
                "%(hour)02d:%(minute)02d:%(second)02d"
            )

    def bind_processor(self, dialect):
        datetime_datetime = datetime.datetime
        datetime_date = datetime.date
        format = self._storage_format

        def process(value):
            if value is None:
                return None
            elif isinstance(value, datetime_datetime):
                return format % {
                    'year': value.year,
                    'month': value.month,
                    'day': value.day,
                    'hour': value.hour,
                    'minute': value.minute,
                    'second': value.second,
                    'microsecond': value.microsecond,
                }
            elif isinstance(value, datetime_date):
                return format % {
                    'year': value.year,
                    'month': value.month,
                    'day': value.day,
                    'hour': 0,
                    'minute': 0,
                    'second': 0,
                    'microsecond': 0,
                }
            else:
                raise TypeError("SQLite DateTime type only accepts Python "
                                "datetime and date objects as input.")
        return process

    def result_processor(self, dialect, coltype):
        if self._reg:
            return processors.str_to_datetime_processor_factory(
                self._reg, datetime.datetime)
        else:
            return processors.str_to_datetime


class DATE(_DateTimeMixin, sqltypes.Date):
    """Represent a Python date object in SQLite using a string.

    The default string storage format is::

        "%(year)04d-%(month)02d-%(day)02d"

    e.g.::

        2011-03-15

    The storage format can be customized to some degree using the
    ``storage_format`` and ``regexp`` parameters, such as::

        import re
        from sqlalchemy.dialects.sqlite import DATE

        d = DATE(
                storage_format="%(month)02d/%(day)02d/%(year)04d",
                regexp=re.compile("(?P<month>\d+)/(?P<day>\d+)/(?P<year>\d+)")
            )

    :param storage_format: format string which will be applied to the
     dict with keys year, month, and day.

    :param regexp: regular expression which will be applied to
     incoming result rows. If the regexp contains named groups, the
     resulting match dict is applied to the Python date() constructor
     as keyword arguments. Otherwise, if positional groups are used, the
     date() constructor is called with positional arguments via
     ``*map(int, match_obj.groups(0))``.
    """

    _storage_format = "%(year)04d-%(month)02d-%(day)02d"

    def bind_processor(self, dialect):
        datetime_date = datetime.date
        format = self._storage_format

        def process(value):
            if value is None:
                return None
            elif isinstance(value, datetime_date):
                return format % {
                    'year': value.year,
                    'month': value.month,
                    'day': value.day,
                }
            else:
                raise TypeError("SQLite Date type only accepts Python "
                                "date objects as input.")
        return process

    def result_processor(self, dialect, coltype):
        if self._reg:
            return processors.str_to_datetime_processor_factory(
                self._reg, datetime.date)
        else:
            return processors.str_to_date


class TIME(_DateTimeMixin, sqltypes.Time):
    """Represent a Python time object in SQLite using a string.

    The default string storage format is::

        "%(hour)02d:%(minute)02d:%(second)02d.%(microsecond)06d"

    e.g.::

        12:05:57.10558

    The storage format can be customized to some degree using the
    ``storage_format`` and ``regexp`` parameters, such as::

        import re
        from sqlalchemy.dialects.sqlite import TIME

        t = TIME(
            storage_format="%(hour)02d-%(minute)02d-%(second)02d-%(microsecond)06d",
            regexp=re.compile("(\d+)-(\d+)-(\d+)-(?:-(\d+))?")
        )

    :param storage_format: format string which will be applied to the dict with
     keys hour, minute, second, and microsecond.

    :param regexp: regular expression which will be applied to incoming result
     rows. If the regexp contains named groups, the resulting match dict is
     applied to the Python time() constructor as keyword arguments. Otherwise,
     if positional groups are used, the time() constructor is called with
     positional arguments via ``*map(int, match_obj.groups(0))``.
    """

    _storage_format = "%(hour)02d:%(minute)02d:%(second)02d.%(microsecond)06d"

    def __init__(self, *args, **kwargs):
        truncate_microseconds = kwargs.pop('truncate_microseconds', False)
        super(TIME, self).__init__(*args, **kwargs)
        if truncate_microseconds:
            assert 'storage_format' not in kwargs, "You can specify only "\
                "one of truncate_microseconds or storage_format."
            assert 'regexp' not in kwargs, "You can specify only one of "\
                "truncate_microseconds or regexp."
            self._storage_format = "%(hour)02d:%(minute)02d:%(second)02d"

    def bind_processor(self, dialect):
        datetime_time = datetime.time
        format = self._storage_format

        def process(value):
            if value is None:
                return None
            elif isinstance(value, datetime_time):
                return format % {
                    'hour': value.hour,
                    'minute': value.minute,
                    'second': value.second,
                    'microsecond': value.microsecond,
                }
            else:
                raise TypeError("SQLite Time type only accepts Python "
                                "time objects as input.")
        return process

    def result_processor(self, dialect, coltype):
        if self._reg:
            return processors.str_to_datetime_processor_factory(
                self._reg, datetime.time)
        else:
            return processors.str_to_time

colspecs = {
    sqltypes.Date: DATE,
    sqltypes.DateTime: DATETIME,
    sqltypes.Time: TIME,
}

ischema_names = {
    'BIGINT': sqltypes.BIGINT,
    'BLOB': sqltypes.BLOB,
    'BOOL': sqltypes.BOOLEAN,
    'BOOLEAN': sqltypes.BOOLEAN,
    'CHAR': sqltypes.CHAR,
    'DATE': sqltypes.DATE,
    'DATETIME': sqltypes.DATETIME,
    'DOUBLE': sqltypes.FLOAT,
    'DECIMAL': sqltypes.DECIMAL,
    'FLOAT': sqltypes.FLOAT,
    'INT': sqltypes.INTEGER,
    'INTEGER': sqltypes.INTEGER,
    'NUMERIC': sqltypes.NUMERIC,
    'REAL': sqltypes.REAL,
    'SMALLINT': sqltypes.SMALLINT,
    'TEXT': sqltypes.TEXT,
    'TIME': sqltypes.TIME,
    'TIMESTAMP': sqltypes.TIMESTAMP,
    'VARCHAR': sqltypes.VARCHAR,
    'NVARCHAR': sqltypes.NVARCHAR,
    'NCHAR': sqltypes.NCHAR,
}


class SQLiteCompiler(compiler.SQLCompiler):
    extract_map = util.update_copy(
        compiler.SQLCompiler.extract_map,
        {
            'month': '%m',
            'day': '%d',
            'year': '%Y',
            'second': '%S',
            'hour': '%H',
            'doy': '%j',
            'minute': '%M',
            'epoch': '%s',
            'dow': '%w',
            'week': '%W',
        })

    def visit_now_func(self, fn, **kw):
        return "CURRENT_TIMESTAMP"

    def visit_localtimestamp_func(self, func, **kw):
        return 'DATETIME(CURRENT_TIMESTAMP, "localtime")'

    def visit_true(self, expr, **kw):
        return '1'

    def visit_false(self, expr, **kw):
        return '0'

    def visit_char_length_func(self, fn, **kw):
        return "length%s" % self.function_argspec(fn)

    def visit_cast(self, cast, **kwargs):
        if self.dialect.supports_cast:
            return super(SQLiteCompiler, self).visit_cast(cast, **kwargs)
        else:
            return self.process(cast.clause, **kwargs)

    def visit_extract(self, extract, **kw):
        try:
            return "CAST(STRFTIME('%s', %s) AS INTEGER)" % (
                self.extract_map[extract.field],
                self.process(extract.expr, **kw)
            )
        except KeyError:
            raise exc.CompileError(
                "%s is not a valid extract argument." % extract.field)

    def limit_clause(self, select):
        text = ""
        if select._limit is not None:
            text += "\n LIMIT " + self.process(sql.literal(select._limit))
        if select._offset is not None:
            if select._limit is None:
                text += "\n LIMIT " + self.process(sql.literal(-1))
            text += " OFFSET " + self.process(sql.literal(select._offset))
        else:
            text += " OFFSET " + self.process(sql.literal(0))
        return text

    def for_update_clause(self, select):
        # sqlite has no "FOR UPDATE" AFAICT
        return ''


class SQLiteDDLCompiler(compiler.DDLCompiler):

    def get_column_specification(self, column, **kwargs):
        coltype = self.dialect.type_compiler.process(column.type)
        colspec = self.preparer.format_column(column) + " " + coltype
        default = self.get_column_default_string(column)
        if default is not None:
            colspec += " DEFAULT " + default

        if not column.nullable:
            colspec += " NOT NULL"

        if (column.primary_key and
                column.table.dialect_options['sqlite']['autoincrement'] and
                len(column.table.primary_key.columns) == 1 and
                issubclass(column.type._type_affinity, sqltypes.Integer) and
                not column.foreign_keys):
            colspec += " PRIMARY KEY AUTOINCREMENT"

        return colspec

    def visit_primary_key_constraint(self, constraint):
        # for columns with sqlite_autoincrement=True,
        # the PRIMARY KEY constraint can only be inline
        # with the column itself.
        if len(constraint.columns) == 1:
            c = list(constraint)[0]
            if (c.primary_key and
                    c.table.dialect_options['sqlite']['autoincrement'] and
                    issubclass(c.type._type_affinity, sqltypes.Integer) and
                    not c.foreign_keys):
                return None

        return super(SQLiteDDLCompiler, self).visit_primary_key_constraint(
            constraint)

    def visit_foreign_key_constraint(self, constraint):

        local_table = list(constraint._elements.values())[0].parent.table
        remote_table = list(constraint._elements.values())[0].column.table

        if local_table.schema != remote_table.schema:
            return None
        else:
            return super(SQLiteDDLCompiler, self).visit_foreign_key_constraint(
                constraint)

    def define_constraint_remote_table(self, constraint, table, preparer):
        """Format the remote table clause of a CREATE CONSTRAINT clause."""

        return preparer.format_table(table, use_schema=False)

    def visit_create_index(self, create):
        return super(SQLiteDDLCompiler, self).visit_create_index(
            create, include_table_schema=False)


class SQLiteTypeCompiler(compiler.GenericTypeCompiler):
    def visit_large_binary(self, type_):
        return self.visit_BLOB(type_)


class SQLiteIdentifierPreparer(compiler.IdentifierPreparer):
    reserved_words = set([
        'add', 'after', 'all', 'alter', 'analyze', 'and', 'as', 'asc',
        'attach', 'autoincrement', 'before', 'begin', 'between', 'by',
        'cascade', 'case', 'cast', 'check', 'collate', 'column', 'commit',
        'conflict', 'constraint', 'create', 'cross', 'current_date',
        'current_time', 'current_timestamp', 'database', 'default',
        'deferrable', 'deferred', 'delete', 'desc', 'detach', 'distinct',
        'drop', 'each', 'else', 'end', 'escape', 'except', 'exclusive',
        'explain', 'false', 'fail', 'for', 'foreign', 'from', 'full', 'glob',
        'group', 'having', 'if', 'ignore', 'immediate', 'in', 'index',
        'indexed', 'initially', 'inner', 'insert', 'instead', 'intersect',
        'into', 'is', 'isnull', 'join', 'key', 'left', 'like', 'limit',
        'match', 'natural', 'not', 'notnull', 'null', 'of', 'offset', 'on',
        'or', 'order', 'outer', 'plan', 'pragma', 'primary', 'query',
        'raise', 'references', 'reindex', 'rename', 'replace', 'restrict',
        'right', 'rollback', 'row', 'select', 'set', 'table', 'temp',
        'temporary', 'then', 'to', 'transaction', 'trigger', 'true', 'union',
        'unique', 'update', 'using', 'vacuum', 'values', 'view', 'virtual',
        'when', 'where',
        ])

    def format_index(self, index, use_schema=True, name=None):
        """Prepare a quoted index and schema name."""

        if name is None:
            name = index.name
        result = self.quote(name, index.quote)
        if (not self.omit_schema and
                use_schema and
                getattr(index.table, "schema", None)):
            result = self.quote_schema(index.table.schema,
                                       index.table.quote_schema) + "." + result
        return result


class SQLiteExecutionContext(default.DefaultExecutionContext):
    @util.memoized_property
    def _preserve_raw_colnames(self):
        return self.execution_options.get("sqlite_raw_colnames", False)

    def _translate_colname(self, colname):
        # adjust for dotted column names. SQLite in the case of UNION may store
        # col names as "tablename.colname" in cursor.description
        if not self._preserve_raw_colnames and "." in colname:
            return colname.split(".")[1], colname
        else:
            return colname, None


class SQLiteDialect(default.DefaultDialect):
    name = 'sqlite'
    supports_alter = False
    supports_unicode_statements = True
    supports_unicode_binds = True
    supports_default_values = True
    supports_empty_insert = False
    supports_cast = True
    supports_multivalues_insert = True
    supports_right_nested_joins = False

    default_paramstyle = 'qmark'
    execution_ctx_cls = SQLiteExecutionContext
    statement_compiler = SQLiteCompiler
    ddl_compiler = SQLiteDDLCompiler
    type_compiler = SQLiteTypeCompiler
    preparer = SQLiteIdentifierPreparer
    ischema_names = ischema_names
    colspecs = colspecs
    isolation_level = None

    supports_cast = True
    supports_default_values = True

    construct_arguments = [
        (sa_schema.Table, {
            "autoincrement": False
        })
    ]

    _broken_fk_pragma_quotes = False

    def __init__(self, isolation_level=None, native_datetime=False, **kwargs):
        default.DefaultDialect.__init__(self, **kwargs)
        self.isolation_level = isolation_level

        # this flag used by pysqlite dialect, and perhaps others in the future,
        # to indicate the driver is handling date/timestamp conversions (and
        # perhaps datetime/time as well on some hypothetical driver ?)
        self.native_datetime = native_datetime

        if self.dbapi is not None:
            self.supports_default_values = (
                self.dbapi.sqlite_version_info >= (3, 3, 8))
            self.supports_cast = (
                self.dbapi.sqlite_version_info >= (3, 2, 3))
            self.supports_multivalues_insert = (
                # http://www.sqlite.org/releaselog/3_7_11.html
                self.dbapi.sqlite_version_info >= (3, 7, 11))
            # see http://www.sqlalchemy.org/trac/ticket/2568
            # as well as http://www.sqlite.org/src/info/600482d161
            self._broken_fk_pragma_quotes = (
                self.dbapi.sqlite_version_info < (3, 6, 14))

    _isolation_lookup = {
        'READ UNCOMMITTED': 1,
        'SERIALIZABLE': 0,
    }

    def set_isolation_level(self, connection, level):
        try:
            isolation_level = self._isolation_lookup[level.replace('_', ' ')]
        except KeyError:
            raise exc.ArgumentError(
                "Invalid value '%s' for isolation_level. "
                "Valid isolation levels for %s are %s" %
                (level, self.name, ", ".join(self._isolation_lookup))
                )
        cursor = connection.cursor()
        cursor.execute("PRAGMA read_uncommitted = %d" % isolation_level)
        cursor.close()

    def get_isolation_level(self, connection):
        cursor = connection.cursor()
        cursor.execute('PRAGMA read_uncommitted')
        res = cursor.fetchone()
        if res:
            value = res[0]
        else:
            # http://www.sqlite.org/changes.html#version_3_3_3
            # "Optional READ UNCOMMITTED isolation (instead of the
            # default isolation level of SERIALIZABLE) and
            # table level locking when database connections
            # share a common cache.""
            # pre-SQLite 3.3.0 default to 0
            value = 0
        cursor.close()
        if value == 0:
            return "SERIALIZABLE"
        elif value == 1:
            return "READ UNCOMMITTED"
        else:
            assert False, "Unknown isolation level %s" % value

    def on_connect(self):
        if self.isolation_level is not None:
            def connect(conn):
                self.set_isolation_level(conn, self.isolation_level)
            return connect
        else:
            return None

    @reflection.cache
    def get_table_names(self, connection, schema=None, **kw):
        if schema is not None:
            qschema = self.identifier_preparer.quote_identifier(schema)
            master = '%s.sqlite_master' % qschema
            s = ("SELECT name FROM %s "
                 "WHERE type='table' ORDER BY name") % (master,)
            rs = connection.execute(s)
        else:
            try:
                s = ("SELECT name FROM "
                     " (SELECT * FROM sqlite_master UNION ALL "
                     "  SELECT * FROM sqlite_temp_master) "
                     "WHERE type='table' ORDER BY name")
                rs = connection.execute(s)
            except exc.DBAPIError:
                s = ("SELECT name FROM sqlite_master "
                     "WHERE type='table' ORDER BY name")
                rs = connection.execute(s)

        return [row[0] for row in rs]

    def has_table(self, connection, table_name, schema=None):
        quote = self.identifier_preparer.quote_identifier
        if schema is not None:
            pragma = "PRAGMA %s." % quote(schema)
        else:
            pragma = "PRAGMA "
        qtable = quote(table_name)
        statement = "%stable_info(%s)" % (pragma, qtable)
        cursor = _pragma_cursor(connection.execute(statement))
        row = cursor.fetchone()

        # consume remaining rows, to work around
        # http://www.sqlite.org/cvstrac/tktview?tn=1884
        while not cursor.closed and cursor.fetchone() is not None:
            pass

        return row is not None

    @reflection.cache
    def get_view_names(self, connection, schema=None, **kw):
        if schema is not None:
            qschema = self.identifier_preparer.quote_identifier(schema)
            master = '%s.sqlite_master' % qschema
            s = ("SELECT name FROM %s "
                 "WHERE type='view' ORDER BY name") % (master,)
            rs = connection.execute(s)
        else:
            try:
                s = ("SELECT name FROM "
                     " (SELECT * FROM sqlite_master UNION ALL "
                     "  SELECT * FROM sqlite_temp_master) "
                     "WHERE type='view' ORDER BY name")
                rs = connection.execute(s)
            except exc.DBAPIError:
                s = ("SELECT name FROM sqlite_master "
                     "WHERE type='view' ORDER BY name")
                rs = connection.execute(s)

        return [row[0] for row in rs]

    @reflection.cache
    def get_view_definition(self, connection, view_name, schema=None, **kw):
        if schema is not None:
            qschema = self.identifier_preparer.quote_identifier(schema)
            master = '%s.sqlite_master' % qschema
            s = ("SELECT sql FROM %s WHERE name = '%s'"
                 "AND type='view'") % (master, view_name)
            rs = connection.execute(s)
        else:
            try:
                s = ("SELECT sql FROM "
                     " (SELECT * FROM sqlite_master UNION ALL "
                     "  SELECT * FROM sqlite_temp_master) "
                     "WHERE name = '%s' "
                     "AND type='view'") % view_name
                rs = connection.execute(s)
            except exc.DBAPIError:
                s = ("SELECT sql FROM sqlite_master WHERE name = '%s' "
                     "AND type='view'") % view_name
                rs = connection.execute(s)

        result = rs.fetchall()
        if result:
            return result[0].sql

    @reflection.cache
    def get_columns(self, connection, table_name, schema=None, **kw):
        quote = self.identifier_preparer.quote_identifier
        if schema is not None:
            pragma = "PRAGMA %s." % quote(schema)
        else:
            pragma = "PRAGMA "
        qtable = quote(table_name)
        statement = "%stable_info(%s)" % (pragma, qtable)
        c = _pragma_cursor(connection.execute(statement))

        rows = c.fetchall()
        columns = []
        for row in rows:
            (name, type_, nullable, default, primary_key) = (
                row[1], row[2].upper(), not row[3], row[4], row[5])

            columns.append(self._get_column_info(name, type_, nullable,
                                                 default, primary_key))
        return columns

    def _get_column_info(self, name, type_, nullable, default, primary_key):
        coltype = self._resolve_type_affinity(type_)

        if default is not None:
            default = util.text_type(default)

        return {
            'name': name,
            'type': coltype,
            'nullable': nullable,
            'default': default,
            'autoincrement': default is None,
            'primary_key': primary_key,
        }

    def _resolve_type_affinity(self, type_):
        """Return a data type from a reflected column, using affinity tules.

        SQLite's goal for universal compatibility introduces some complexity
        during reflection, as a column's defined type might not actually be a
        type that SQLite understands - or indeed, my not be defined *at all*.
        Internally, SQLite handles this with a 'data type affinity' for each
        column definition, mapping to one of 'TEXT', 'NUMERIC', 'INTEGER',
        'REAL', or 'NONE' (raw bits). The algorithm that determines this is
        listed in http://www.sqlite.org/datatype3.html section 2.1.

        This method allows SQLAlchemy to support that algorithm, while still
        providing access to smarter reflection utilities by regcognizing
        column definitions that SQLite only supports through affinity (like
        DATE and DOUBLE).

        """
        match = re.match(r'([\w ]+)(\(.*?\))?', type_)
        if match:
            coltype = match.group(1)
            args = match.group(2)
        else:
            coltype = ''
            args = ''

        if coltype in self.ischema_names:
            coltype = self.ischema_names[coltype]
        elif 'INT' in coltype:
            coltype = sqltypes.INTEGER
        elif 'CHAR' in coltype or 'CLOB' in coltype or 'TEXT' in coltype:
            coltype = sqltypes.TEXT
        elif 'BLOB' in coltype or not coltype:
            coltype = sqltypes.NullType
        elif 'REAL' in coltype or 'FLOA' in coltype or 'DOUB' in coltype:
            coltype = sqltypes.REAL
        else:
            coltype = sqltypes.NUMERIC

        if args is not None:
            args = re.findall(r'(\d+)', args)
            try:
                coltype = coltype(*[int(a) for a in args])
            except TypeError:
                util.warn(
                        "Could not instantiate type %s with "
                        "reflected arguments %s; using no arguments." %
                        (coltype, args))
                coltype = coltype()
        else:
            coltype = coltype()

        return coltype

    @reflection.cache
    def get_pk_constraint(self, connection, table_name, schema=None, **kw):
        cols = self.get_columns(connection, table_name, schema, **kw)
        pkeys = []
        for col in cols:
            if col['primary_key']:
                pkeys.append(col['name'])
        return {'constrained_columns': pkeys, 'name': None}

    @reflection.cache
    def get_foreign_keys(self, connection, table_name, schema=None, **kw):
        quote = self.identifier_preparer.quote_identifier
        if schema is not None:
            pragma = "PRAGMA %s." % quote(schema)
        else:
            pragma = "PRAGMA "
        qtable = quote(table_name)
        statement = "%sforeign_key_list(%s)" % (pragma, qtable)
        c = _pragma_cursor(connection.execute(statement))
        fkeys = []
        fks = {}
        while True:
            row = c.fetchone()
            if row is None:
                break
            (numerical_id, rtbl, lcol, rcol) = (row[0], row[2], row[3], row[4])

            self._parse_fk(fks, fkeys, numerical_id, rtbl, lcol, rcol)
        return fkeys

    def _parse_fk(self, fks, fkeys, numerical_id, rtbl, lcol, rcol):
        # sqlite won't return rcol if the table was created with REFERENCES
        # <tablename>, no col
        if rcol is None:
            rcol = lcol

        if self._broken_fk_pragma_quotes:
            rtbl = re.sub(r'^[\"\[`\']|[\"\]`\']$', '', rtbl)

        try:
            fk = fks[numerical_id]
        except KeyError:
            fk = {
                'name': None,
                'constrained_columns': [],
                'referred_schema': None,
                'referred_table': rtbl,
                'referred_columns': [],
            }
            fkeys.append(fk)
            fks[numerical_id] = fk

        if lcol not in fk['constrained_columns']:
            fk['constrained_columns'].append(lcol)
        if rcol not in fk['referred_columns']:
            fk['referred_columns'].append(rcol)
        return fk

    @reflection.cache
    def get_indexes(self, connection, table_name, schema=None, **kw):
        quote = self.identifier_preparer.quote_identifier
        if schema is not None:
            pragma = "PRAGMA %s." % quote(schema)
        else:
            pragma = "PRAGMA "
        include_auto_indexes = kw.pop('include_auto_indexes', False)
        qtable = quote(table_name)
        statement = "%sindex_list(%s)" % (pragma, qtable)
        c = _pragma_cursor(connection.execute(statement))
        indexes = []
        while True:
            row = c.fetchone()
            if row is None:
                break
            # ignore implicit primary key index.
            # http://www.mail-archive.com/sqlite-users@sqlite.org/msg30517.html
            elif (not include_auto_indexes and
                  row[1].startswith('sqlite_autoindex')):
                continue

            indexes.append(dict(name=row[1], column_names=[], unique=row[2]))
        # loop thru unique indexes to get the column names.
        for idx in indexes:
            statement = "%sindex_info(%s)" % (pragma, quote(idx['name']))
            c = connection.execute(statement)
            cols = idx['column_names']
            while True:
                row = c.fetchone()
                if row is None:
                    break
                cols.append(row[2])
        return indexes

    @reflection.cache
    def get_unique_constraints(self, connection, table_name,
                               schema=None, **kw):
        UNIQUE_SQL = """
            SELECT sql
            FROM
                sqlite_master
            WHERE
                type='table' AND
                name=:table_name
        """
        c = connection.execute(UNIQUE_SQL, table_name=table_name)
        table_data = c.fetchone()[0]

        UNIQUE_PATTERN = 'CONSTRAINT (\w+) UNIQUE \(([^\)]+)\)'
        return [
            {'name': name,
             'column_names': [col.strip(' "') for col in cols.split(',')]}
            for name, cols in re.findall(UNIQUE_PATTERN, table_data)
        ]


def _pragma_cursor(cursor):
    """work around SQLite issue whereby cursor.description
    is blank when PRAGMA returns no rows."""

    if cursor.closed:
        cursor.fetchone = lambda: None
        cursor.fetchall = lambda: []
    return cursor