# Source code for sqlobject.dbconnection

    import atexit
    import inspect
    import sys
    import os
    import threading
    import types
    try:
        from urlparse import urlparse, parse_qsl
        from urllib import unquote, quote, urlencode
    except ImportError:
        from urllib.parse import urlparse, parse_qsl, unquote, quote, urlencode

    import warnings
    import weakref

    from . import classregistry
    from . import col
    from . import sqlbuilder
    from .cache import CacheSet
    from .compat import PY2, string_type, unicode_type
    from .converters import sqlrepr
    from .events import send, CommitSignal, RollbackSignal
    from .util.threadinglocal import local as threading_local

    warnings.filterwarnings("ignore", "DB-API extension cursor.lastrowid used")

    def _closeConnection(ref):
        conn = ref()
        if conn is not None:
            conn.close()

    class ConsoleWriter:
        def __init__(self, connection, loglevel):
            # loglevel: None or empty string for stdout; or 'stderr'
            self.loglevel = loglevel or "stdout"
            self.dbEncoding = getattr(connection, "dbEncoding", None) or "ascii"

        def write(self, text):
            logfile = getattr(sys, self.loglevel)
            if PY2 and isinstance(text, unicode_type):
                try:
                    text = text.encode(self.dbEncoding)
                except UnicodeEncodeError:
                    text = repr(text)[2:-1]  # Remove u'...' from the repr
            logfile.write(text + '\n')

    class LogWriter:
        def __init__(self, connection, logger, loglevel):
            self.logger = logger
            self.loglevel = loglevel
            self.logmethod = getattr(logger, loglevel)

        def write(self, text):
            self.logmethod(text)

    def makeDebugWriter(connection, loggerName, loglevel):
        if not loggerName:
            return ConsoleWriter(connection, loglevel)
        import logging
        logger = logging.getLogger(loggerName)
        return LogWriter(connection, logger, loglevel)

    class Boolean(object):
        """A bool class that also understands some special string keywords

        Understands: yes/no, true/false, on/off, 1/0, case ignored.

        """
        _keywords = {'1': True, 'yes': True, 'true': True, 'on': True,
                     '0': False, 'no': False, 'false': False, 'off': False}

        def __new__(cls, value):
            try:
                return Boolean._keywords[value.lower()]
            except (AttributeError, KeyError):
                return bool(value)

    class DBConnection:

        def __init__(self, name=None, debug=False, debugOutput=False,
                     cache=True, style=None, autoCommit=True,
                     debugThreading=False, registry=None,
                     logger=None, loglevel=None):
            self.name = name
            self.debug = Boolean(debug)
            self.debugOutput = Boolean(debugOutput)
            self.debugThreading = Boolean(debugThreading)
            self.debugWriter = makeDebugWriter(self, logger, loglevel)
            self.doCache = Boolean(cache)
            self.cache = CacheSet(cache=self.doCache)
            self.style = style
            self._connectionNumbers = {}
            self._connectionCount = 1
            self.autoCommit = Boolean(autoCommit)
            self.registry = registry or None
            classregistry.registry(self.registry).addCallback(self.soClassAdded)
            registerConnectionInstance(self)
            atexit.register(_closeConnection, weakref.ref(self))

        def oldUri(self):
            auth = getattr(self, 'user', '') or ''
            if auth:
                if self.password:
                    auth += ':' + self.password
                auth += '@'
            else:
                assert not getattr(self, 'password', None), (
                    'URIs cannot express passwords without usernames')
            uri = '%s://%s' % (self.dbName, auth)
            if self.host:
                uri += self.host
                if self.port:
                    uri += ':%d' % self.port
            uri += '/'
            db = self.db
            if db.startswith('/'):
                db = db[1:]
            return uri + db

        def uri(self):
            auth = getattr(self, 'user', '') or ''
            if auth:
                auth = quote(auth)
                if self.password:
                    auth += ':' + quote(self.password)
                auth += '@'
            else:
                assert not getattr(self, 'password', None), (
                    'URIs cannot express passwords without usernames')
            uri = '%s://%s' % (self.dbName, auth)
            if self.host:
                uri += self.host
                if self.port:
                    uri += ':%d' % self.port
            uri += '/'
            db = self.db
            if db.startswith('/'):
                db = db[1:]
            return uri + quote(db)

        @classmethod
        def connectionFromOldURI(cls, uri):
            return cls._connectionFromParams(*cls._parseOldURI(uri))

        @classmethod
        def connectionFromURI(cls, uri):
            return cls._connectionFromParams(*cls._parseURI(uri))

        @staticmethod
        def _parseOldURI(uri):
            schema, rest = uri.split(':', 1)
            assert rest.startswith('/'), \
                "URIs must start with scheme:/ -- " \
                "you did not include a / (in %r)" % rest
            if rest.startswith('/') and not rest.startswith('//'):
                host = None
                rest = rest[1:]
            elif rest.startswith('///'):
                host = None
                rest = rest[3:]
            else:
                rest = rest[2:]
                if rest.find('/') == -1:
                    host = rest
                    rest = ''
                else:
                    host, rest = rest.split('/', 1)
            if host and host.find('@') != -1:
                user, host = host.rsplit('@', 1)
                if user.find(':') != -1:
                    user, password = user.split(':', 1)
                else:
                    password = None
            else:
                user = password = None
            if host and host.find(':') != -1:
                _host, port = host.split(':')
                try:
                    port = int(port)
                except ValueError:
                    raise ValueError("port must be integer, "
                                     "got '%s' instead" % port)
                if not (1 <= port <= 65535):
                    raise ValueError("port must be integer in the range 1-65535, "
                                     "got '%d' instead" % port)
                host = _host
            else:
                port = None
            path = '/' + rest
            if os.name == 'nt':
                if (len(rest) > 1) and (rest[1] == '|'):
                    path = "%s:%s" % (rest[0], rest[2:])
            args = {}
            if path.find('?') != -1:
                path, arglist = path.split('?', 1)
                arglist = arglist.split('&')
                for single in arglist:
                    argname, argvalue = single.split('=', 1)
                    argvalue = unquote(argvalue)
                    args[argname] = argvalue
            return user, password, host, port, path, args

        @staticmethod
        def _parseURI(uri):
            parsed = urlparse(uri)
            host, path = parsed.hostname, parsed.path
            user, password, port = None, None, None
            if parsed.username:
                user = unquote(parsed.username)
            if parsed.password:
                password = unquote(parsed.password)
            if parsed.port:
                port = int(parsed.port)

            path = unquote(path)
            if (os.name == 'nt') and (len(path) > 2):
                # Preserve backward compatibility with URIs like /C|/path;
                # replace '|' by ':'
                if path[2] == '|':
                    path = "%s:%s" % (path[0:2], path[3:])
                # Remove leading slash
                if (path[0] == '/') and (path[2] == ':'):
                    path = path[1:]

            query = parsed.query
            # hash-tag / fragment is ignored

            args = {}
            if query:
                for name, value in parse_qsl(query):
                    args[name] = value

            return user, password, host, port, path, args

        def soClassAdded(self, soClass):
            """
            This is called for each new class; we use this opportunity
            to create an instance method that is bound to the class
            and this connection.
            """
            name = soClass.__name__
            assert not hasattr(self, name), (
                "Connection %r already has an attribute with the name "
                "%r (and you just created the conflicting class %r)"
                % (self, name, soClass))
            setattr(self, name, ConnWrapper(soClass, self))

        def expireAll(self):
            """
            Expire all instances of objects for this connection.
            """
            cache_set = self.cache
            cache_set.weakrefAll()
            for item in cache_set.getAll():
                item.expire()

    class ConnWrapper(object):

        """
        This represents a SQLObject class that is bound to a specific
        connection (instances have a connection instance variable, but
        classes are global, so this is binds the connection variable
        lazily when a class method is accessed)
        """
        # @@: methods that take connection arguments should be explicitly
        # marked up instead of the implicit use of a connection argument
        # and inspect.getargspec()

        def __init__(self, soClass, connection):
            self._soClass = soClass
            self._connection = connection

        def __call__(self, *args, **kw):
            kw['connection'] = self._connection
            return self._soClass(*args, **kw)

        def __getattr__(self, attr):
            meth = getattr(self._soClass, attr)
            if not isinstance(meth, types.MethodType):
                # We don't need to wrap non-methods
                return meth
            try:
                takes_conn = meth.takes_connection
            except AttributeError:
                args, varargs, varkw, defaults = inspect.getargspec(meth)
                assert not varkw and not varargs, (
                    "I cannot tell whether I must wrap this method, "
                    "because it takes **kw: %r"
                    % meth)
                takes_conn = 'connection' in args
                meth.__func__.takes_connection = takes_conn
            if not takes_conn:
                return meth
            return ConnMethodWrapper(meth, self._connection)

    class ConnMethodWrapper(object):

        def __init__(self, method, connection):
            self._method = method
            self._connection = connection

        def __getattr__(self, attr):
            return getattr(self._method, attr)

        def __call__(self, *args, **kw):
            kw['connection'] = self._connection
            return self._method(*args, **kw)

        def __repr__(self):
            return '<Wrapped %r with connection %r>' % (
                self._method, self._connection)

    class DBAPI(DBConnection):

        """
        Subclass must define a `makeConnection()` method, which
        returns a newly-created connection object.

        ``queryInsertID`` must also be defined.
        """
        dbName = None

        def __init__(self, **kw):
            self._pool = []
            self._poolLock = threading.Lock()
            DBConnection.__init__(self, **kw)
            self._binaryType = type(self.module.Binary(b''))

        def _runWithConnection(self, meth, *args):
            conn = self.getConnection()
            try:
                val = meth(conn, *args)
            finally:
                self.releaseConnection(conn)
            return val

        def getConnection(self):
            self._poolLock.acquire()
            try:
                if not self._pool:
                    conn = self.makeConnection()
                    self._connectionNumbers[id(conn)] = self._connectionCount
                    self._connectionCount += 1
                else:
                    conn = self._pool.pop()
                if self.debug:
                    s = 'ACQUIRE'
                    if self._pool is not None:
                        s += ' pool=[%s]' % ', '.join(
                            [str(self._connectionNumbers[id(v)])
                                for v in self._pool])
                    self.printDebug(conn, s, 'Pool')
                return conn
            finally:
                self._poolLock.release()

        def releaseConnection(self, conn, explicit=False):
            if self.debug:
                if explicit:
                    s = 'RELEASE (explicit)'
                else:
                    s = 'RELEASE (implicit, autocommit=%s)' % self.autoCommit
                if self._pool is None:
                    s += ' no pooling'
                else:
                    s += ' pool=[%s]' % ', '.join(
                        [str(self._connectionNumbers[id(v)]) for v in self._pool])
                self.printDebug(conn, s, 'Pool')
            if self.supportTransactions and not explicit:
                if self.autoCommit == 'exception':
                    if self.debug:
                        self.printDebug(conn, 'auto/exception', 'ROLLBACK')
                    conn.rollback()
                    raise Exception('Object used outside of a transaction; '
                                    'implicit COMMIT or ROLLBACK not allowed')
                elif self.autoCommit:
                    if self.debug:
                        self.printDebug(conn, 'auto', 'COMMIT')
                    if not getattr(conn, 'autocommit', False):
                        conn.commit()
                else:
                    if self.debug:
                        self.printDebug(conn, 'auto', 'ROLLBACK')
                    conn.rollback()
            if self._pool is not None:
                if conn not in self._pool:
                    # @@: We can get duplicate releasing of connections with
                    # the __del__ in Iteration (unfortunately, not sure why
                    # it happens)
                    self._pool.insert(0, conn)
            else:
                conn.close()

        def printDebug(self, conn, s, name, type='query'):
            if name == 'Pool' and self.debug != 'Pool':
                return
            if type == 'query':
                sep = ': '
            else:
                sep = '->'
                s = repr(s)
            n = self._connectionNumbers[id(conn)]
            spaces = ' ' * (8 - len(name))
            if self.debugThreading:
                threadName = threading.currentThread().getName()
                threadName = (':' + threadName + ' ' * (8 - len(threadName)))
            else:
                threadName = ''
            msg = '%(n)2i%(threadName)s/%(name)s%(spaces)s%(sep)s %(s)s' % locals()
            self.debugWriter.write(msg)

        def _executeRetry(self, conn, cursor, query):
            if self.debug:
                self.printDebug(conn, query, 'QueryR')
            return cursor.execute(query)

        def _query(self, conn, s):
            if self.debug:
                self.printDebug(conn, s, 'Query')
            c = conn.cursor()
            self._executeRetry(conn, c, s)
            c.close()

        def query(self, s):
            return self._runWithConnection(self._query, s)

        def _queryAll(self, conn, s):
            if self.debug:
                self.printDebug(conn, s, 'QueryAll')
            c = conn.cursor()
            self._executeRetry(conn, c, s)
            value = c.fetchall()
            c.close()
            if self.debugOutput:
                self.printDebug(conn, value, 'QueryAll', 'result')
            return value

        def queryAll(self, s):
            return self._runWithConnection(self._queryAll, s)

        def _queryAllDescription(self, conn, s):
            """
            Like queryAll, but returns (description, rows), where the
            description is cursor.description (which gives row types)
            """
            if self.debug:
                self.printDebug(conn, s, 'QueryAllDesc')
            c = conn.cursor()
            self._executeRetry(conn, c, s)
            value = c.fetchall()
            c.close()
            if self.debugOutput:
                self.printDebug(conn, value, 'QueryAll', 'result')
            return c.description, value

        def queryAllDescription(self, s):
            return self._runWithConnection(self._queryAllDescription, s)

        def _queryOne(self, conn, s):
            if self.debug:
                self.printDebug(conn, s, 'QueryOne')
            c = conn.cursor()
            self._executeRetry(conn, c, s)
            value = c.fetchone()
            c.close()
            if self.debugOutput:
                self.printDebug(conn, value, 'QueryOne', 'result')
            return value

        def queryOne(self, s):
            return self._runWithConnection(self._queryOne, s)

        def _insertSQL(self, table, names, values):
            return ("INSERT INTO %s (%s) VALUES (%s)" %
                    (table, ', '.join(names),
                     ', '.join([self.sqlrepr(v) for v in values])))

        def transaction(self):
            return Transaction(self)

        def queryInsertID(self, soInstance, id, names, values):
            return self._runWithConnection(self._queryInsertID, soInstance, id,
                                           names, values)

        def iterSelect(self, select):
            return select.IterationClass(self, self.getConnection(),
                                         select, keepConnection=False)

        def accumulateSelect(self, select, *expressions):
            """ Apply an accumulate function(s) (SUM, COUNT, MIN, AVG, MAX, etc...)
                to the select object.
            """
            q = select.queryForSelect().newItems(expressions).\
                unlimited().orderBy(None)
            q = self.sqlrepr(q)
            val = self.queryOne(q)
            if len(expressions) == 1:
                val = val[0]
            return val

        def queryForSelect(self, select):
            return self.sqlrepr(select.queryForSelect())

        def _SO_createJoinTable(self, join):
            self.query(self._SO_createJoinTableSQL(join))

        def _SO_createJoinTableSQL(self, join):
            return ('CREATE TABLE %s (\n%s %s,\n%s %s\n)' %
                    (join.intermediateTable,
                     join.joinColumn,
                     self.joinSQLType(join),
                     join.otherColumn,
                     self.joinSQLType(join)))

        def _SO_dropJoinTable(self, join):
            self.query("DROP TABLE %s" % join.intermediateTable)

        def _SO_createIndex(self, soClass, index):
            self.query(self.createIndexSQL(soClass, index))

        def createIndexSQL(self, soClass, index):
            assert 0, 'Implement in subclasses'

        def createTable(self, soClass):
            createSql, constraints = self.createTableSQL(soClass)
            self.query(createSql)

            return constraints

        def createReferenceConstraints(self, soClass):
            refConstraints = [self.createReferenceConstraint(soClass, column)
                              for column in soClass.sqlmeta.columnList
                              if isinstance(column, col.SOForeignKey)]
            refConstraintDefs = [constraint for constraint in refConstraints
                                 if constraint]
            return refConstraintDefs

        def createSQL(self, soClass):
            tableCreateSQLs = getattr(soClass.sqlmeta, 'createSQL', None)
            if tableCreateSQLs:
                assert isinstance(tableCreateSQLs, (str, list, dict, tuple)), (
                    '%s.sqlmeta.createSQL must be a str, list, dict or tuple.' %
                    (soClass.__name__))
                if isinstance(tableCreateSQLs, dict):
                    tableCreateSQLs = tableCreateSQLs.get(
                        soClass._connection.dbName, [])
                if isinstance(tableCreateSQLs, str):
                    tableCreateSQLs = [tableCreateSQLs]
                if isinstance(tableCreateSQLs, tuple):
                    tableCreateSQLs = list(tableCreateSQLs)
                assert isinstance(tableCreateSQLs, list), (
                    'Unable to create a list from %s.sqlmeta.createSQL' %
                    (soClass.__name__))
            return tableCreateSQLs or []

        def createTableSQL(self, soClass):
            constraints = self.createReferenceConstraints(soClass)
            extraSQL = self.createSQL(soClass)
            createSql = ('CREATE TABLE %s (\n%s\n)' %
                         (soClass.sqlmeta.table, self.createColumns(soClass)))
            return createSql, constraints + extraSQL

        def createColumns(self, soClass):
            columnDefs = [self.createIDColumn(soClass)] \
                + [self.createColumn(soClass, col)
                   for col in soClass.sqlmeta.columnList]
            return ",\n".join(["    %s" % c for c in columnDefs])

        def createReferenceConstraint(self, soClass, col):
            assert 0, "Implement in subclasses"

        def createColumn(self, soClass, col):
            assert 0, "Implement in subclasses"

        def dropTable(self, tableName, cascade=False):
            self.query("DROP TABLE %s" % tableName)

        def clearTable(self, tableName):
            # 3-03 @@: Should this have a WHERE 1 = 1 or similar
            # clause?  In some configurations without the WHERE clause
            # the query won't go through, but maybe we shouldn't override
            # that.
            self.query("DELETE FROM %s" % tableName)

        def createBinary(self, value):
            """
            Create a binary object wrapper for the given database.
            """
            # Default is Binary() function from the connection driver.
            return self.module.Binary(value)

        # The _SO_* series of methods are sorts of "friend" methods
        # with SQLObject.  They grab values from the SQLObject instances
        # or classes freely, but keep the SQLObject class from accessing
        # the database directly.  This way no SQL is actually created
        # in the SQLObject class.

        def _SO_update(self, so, values):
            self.query("UPDATE %s SET %s WHERE %s = (%s)" %
                       (so.sqlmeta.table,
                        ", ".join(["%s = (%s)" % (dbName, self.sqlrepr(value))
                                   for dbName, value in values]),
                        so.sqlmeta.idName,
                        self.sqlrepr(so.id)))

        def _SO_selectOne(self, so, columnNames):
            return self._SO_selectOneAlt(so, columnNames, so.q.id == so.id)

        def _SO_selectOneAlt(self, so, columnNames, condition):
            if columnNames:
                columns = [isinstance(x, string_type)
                           and sqlbuilder.SQLConstant(x)
                           or x for x in columnNames]
            else:
                columns = None
            return self.queryOne(self.sqlrepr(sqlbuilder.Select(
                columns, staticTables=[so.sqlmeta.table], clause=condition)))

        def _SO_delete(self, so):
            self.query("DELETE FROM %s WHERE %s = (%s)" %
                       (so.sqlmeta.table,
                        so.sqlmeta.idName,
                        self.sqlrepr(so.id)))

        def _SO_selectJoin(self, soClass, column, value):
            return self.queryAll("SELECT %s FROM %s WHERE %s = (%s)" %
                                 (soClass.sqlmeta.idName,
                                  soClass.sqlmeta.table,
                                  column,
                                  self.sqlrepr(value)))

        def _SO_intermediateJoin(self, table, getColumn, joinColumn, value):
            return self.queryAll("SELECT %s FROM %s WHERE %s = (%s)" %
                                 (getColumn,
                                  table,
                                  joinColumn,
                                  self.sqlrepr(value)))

        def _SO_intermediateDelete(self, table, firstColumn, firstValue,
                                   secondColumn, secondValue):
            self.query("DELETE FROM %s WHERE %s = (%s) AND %s = (%s)" %
                       (table,
                        firstColumn,
                        self.sqlrepr(firstValue),
                        secondColumn,
                        self.sqlrepr(secondValue)))

        def _SO_intermediateInsert(self, table, firstColumn, firstValue,
                                   secondColumn, secondValue):
            self.query("INSERT INTO %s (%s, %s) VALUES (%s, %s)" %
                       (table,
                        firstColumn,
                        secondColumn,
                        self.sqlrepr(firstValue),
                        self.sqlrepr(secondValue)))

        def _SO_columnClause(self, soClass, kw):
            from . import main
            data = []
            if 'id' in kw:
                data.append((soClass.sqlmeta.idName, kw.pop('id')))
            for soColumn in soClass.sqlmeta.columnList:
                key = soColumn.name
                if key in kw:
                    val = kw.pop(key)
                    if soColumn.from_python:
                        val = soColumn.from_python(
                            val,
                            sqlbuilder.SQLObjectState(soClass, connection=self))
                    data.append((soColumn.dbName, val))
                elif soColumn.foreignName in kw:
                    obj = kw.pop(soColumn.foreignName)
                    if isinstance(obj, main.SQLObject):
                        data.append((soColumn.dbName, obj.id))
                    else:
                        data.append((soColumn.dbName, obj))
            if kw:
                # pick the first key from kw to use to raise the error,
                raise TypeError("got an unexpected keyword argument(s): "
                                "%r" % kw.keys())

            if not data:
                return None
            return ' AND '.join(
                ['%s %s %s' %
                 (dbName, "IS" if value is None else "=", self.sqlrepr(value))
                 for dbName, value
                 in data])

        def sqlrepr(self, v):
            return sqlrepr(v, self.dbName)

        def __del__(self):
            self.close()

        def close(self):
            if not hasattr(self, '_pool'):
                # Probably there was an exception while creating this
                # instance, so it is incomplete.
                return
            if not self._pool:
                return
            self._poolLock.acquire()
            try:
                if not self._pool:  # _pool could be filled in a different thread
                    return
                conns = self._pool[:]
                self._pool[:] = []
                for conn in conns:
                    try:
                        conn.close()
                    except self.module.Error:
                        pass
                del conn
                del conns
            finally:
                self._poolLock.release()

        def createEmptyDatabase(self):
            """
            Create an empty database.
            """
            raise NotImplementedError

        def make_odbc_conn_str(self, odb_source, db, host=None, port=None,
                               user=None, password=None):
            odbc_conn_parts = ['Driver={%s}' % odb_source]
            for odbc_keyword, value in \
                    zip(self.odbc_keywords, (host, port, user, password, db)):
                if value is not None:
                    odbc_conn_parts.append('%s=%s' % (odbc_keyword, value))
            self.odbc_conn_str = ';'.join(odbc_conn_parts)

    class Iteration(object):

        def __init__(self, dbconn, rawconn, select, keepConnection=False):
            self.dbconn = dbconn
            self.rawconn = rawconn
            self.select = select
            self.keepConnection = keepConnection
            self.cursor = rawconn.cursor()
            self.query = self.dbconn.queryForSelect(select)
            if dbconn.debug:
                dbconn.printDebug(rawconn, self.query, 'Select')
            self.dbconn._executeRetry(self.rawconn, self.cursor, self.query)

        def __iter__(self):
            return self

        def __next__(self):
            return self.next()

        def next(self):
            result = self.cursor.fetchone()
            if result is None:
                self._cleanup()
                raise StopIteration
            if result[0] is None:
                return None
            if self.select.ops.get('lazyColumns', 0):
                obj = self.select.sourceClass.get(result[0],
                                                  connection=self.dbconn)
                return obj
            else:
                obj = self.select.sourceClass.get(result[0],
                                                  selectResults=result[1:],
                                                  connection=self.dbconn)
                return obj

        def _cleanup(self):
            if getattr(self, 'query', None) is None:
                # already cleaned up
                return
            self.cursor.close()
            if not self.keepConnection:
                self.dbconn.releaseConnection(self.rawconn)
            self.query = self.dbconn = self.rawconn = \
                self.select = self.cursor = None

        def __del__(self):
            self._cleanup()

    class Transaction(object):

        def __init__(self, dbConnection):
            # this is to skip __del__ in case of an exception in this __init__
            self._obsolete = True
            self._dbConnection = dbConnection
            self._connection = dbConnection.getConnection()
            self._dbConnection._setAutoCommit(self._connection, False)
            self.cache = CacheSet(cache=dbConnection.doCache)
            self._deletedCache = {}
            self._obsolete = False

        def assertActive(self):
            assert not self._obsolete, \
                "This transaction has already gone through ROLLBACK; " \
                "begin another transaction"

        def query(self, s):
            self.assertActive()
            return self._dbConnection._query(self._connection, s)

        def queryAll(self, s):
            self.assertActive()
            return self._dbConnection._queryAll(self._connection, s)

        def queryOne(self, s):
            self.assertActive()
            return self._dbConnection._queryOne(self._connection, s)

        def queryInsertID(self, soInstance, id, names, values):
            self.assertActive()
            return self._dbConnection._queryInsertID(
                self._connection, soInstance, id, names, values)

        def iterSelect(self, select):
            self.assertActive()
            # We can't keep the cursor open with results in a transaction,
            # because we might want to use the connection while we're
            # still iterating through the results.
            # @@: But would it be okay for psycopg, with threadsafety
            # level 2?
            return iter(list(select.IterationClass(self, self._connection,
                                                   select, keepConnection=True)))

        def _SO_delete(self, inst):
            cls = inst.__class__.__name__
            if cls not in self._deletedCache:
                self._deletedCache[cls] = []
            self._deletedCache[cls].append(inst.id)
            if PY2:
                meth = types.MethodType(self._dbConnection._SO_delete.__func__,
                                        self, self.__class__)
            else:
                meth = types.MethodType(self._dbConnection._SO_delete.__func__,
                                        self)
            return meth(inst)

        def commit(self, close=False):
            if self._obsolete:
                # @@: is it okay to get extraneous commits?
                return
            if self._dbConnection.debug:
                self._dbConnection.printDebug(self._connection, '', 'COMMIT')
            self._send_event(CommitSignal)
            self._connection.commit()
            subCaches = [(sub[0], sub[1].allIDs())
                         for sub in self.cache.allSubCachesByClassNames().items()]
            subCaches.extend([(x[0], x[1]) for x in self._deletedCache.items()])
            for cls, ids in subCaches:
                for id in list(ids):
                    inst = self._dbConnection.cache.tryGetByName(id, cls)
                    if inst is not None:
                        inst.expire()
            if close:
                self._makeObsolete()

        def rollback(self):
            if self._obsolete:
                # @@: is it okay to get extraneous rollbacks?
                return
            if self._dbConnection.debug:
                self._dbConnection.printDebug(self._connection, '', 'ROLLBACK')
            subCaches = [(sub, sub.allIDs()) for sub in self.cache.allSubCaches()]
            self._send_event(RollbackSignal)
            self._connection.rollback()

            for subCache, ids in subCaches:
                for id in list(ids):
                    inst = subCache.tryGet(id)
                    if inst is not None:
                        inst.expire()
            self._makeObsolete()

        def _send_event(self, signal):
            """
            Pushes a list of class_names and related ids in cache.
            :param signal: Type of event signal to use
            """
            cached_classes_and_ids = [
                (class_name, cache.allIDs()) for class_name, cache in
                self.cache.allSubCachesByClassNames().items()
            ]

            if cached_classes_and_ids:
                from .main import sqlmeta  # Import here to avoid circular import
                send(signal, sqlmeta, cached_classes_and_ids)

        def __getattr__(self, attr):
            """
            If nothing else works, let the parent connection handle it.
            Except with this transaction as 'self'.  Poor man's
            acquisition?  Bad programming?  Okay, maybe.
            """
            self.assertActive()
            attr = getattr(self._dbConnection, attr)
            try:
                func = attr.__func__
            except AttributeError:
                if isinstance(attr, ConnWrapper):
                    return ConnWrapper(attr._soClass, self)
                else:
                    return attr
            else:
                if PY2:
                    meth = types.MethodType(func, self, self.__class__)
                else:
                    meth = types.MethodType(func, self)
                return meth

        def _makeObsolete(self):
            self._obsolete = True
            if self._dbConnection.autoCommit:
                self._dbConnection._setAutoCommit(self._connection, True)
            self._dbConnection.releaseConnection(self._connection,
                                                 explicit=True)
            self._connection = None
            self._deletedCache = {}

        def begin(self):
            # @@: Should we do this, or should begin() be a no-op when we're
            # not already obsolete?
            assert self._obsolete, \
                "You cannot begin a new transaction session " \
                "without rolling back this one"
            self._obsolete = False
            self._connection = self._dbConnection.getConnection()
            self._dbConnection._setAutoCommit(self._connection, False)

        def __del__(self):
            if self._obsolete:
                return
            self.rollback()

        def close(self):
            raise TypeError('You cannot just close transaction - '
                            'you should either call rollback(), commit() '
                            'or commit(close=True) '
                            'to close the underlying connection.')

    class ConnectionHub(object):

        """
        This object serves as a hub for connections, so that you can pass
        in a ConnectionHub to a SQLObject subclass as though it was a
        connection, but actually bind a real database connection later.
        You can also bind connections on a per-thread basis.

        You must hang onto the original ConnectionHub instance, as you
        cannot retrieve it again from the class or instance.

        To use the hub, do something like::

            hub = ConnectionHub()
            class MyClass(SQLObject):
                _connection = hub

            hub.threadConnection = connectionFromURI('...')

        """

        def __init__(self):
            self.threadingLocal = threading_local()

        def __get__(self, obj, type=None):
            # I'm a little surprised we have to do this, but apparently
            # the object's private dictionary of attributes doesn't
            # override this descriptor.
            if (obj is not None) and '_connection' in obj.__dict__:
                return obj.__dict__['_connection']
            return self.getConnection()

        def __set__(self, obj, value):
            obj.__dict__['_connection'] = value

        def getConnection(self):
            try:
                connection = self.threadingLocal.connection
                if isinstance(connection, string_type):
                    connection = connectionForURI(connection)
                    self.threadingLocal.connection = connection
            except AttributeError:
                try:
                    connection = self.processConnection
                    if isinstance(connection, string_type):
                        connection = connectionForURI(connection)
                        self.processConnection = connection
                except AttributeError:
                    raise AttributeError(
                        "No connection has been defined for this thread "
                        "or process")
            return connection

        def doInTransaction(self, func, *args, **kw):
            """
            This routine can be used to run a function in a transaction,
            rolling the transaction back if any exception is raised from
            that function, and committing otherwise.

            Use like::

                sqlhub.doInTransaction(process_request, os.environ)

            This will run ``process_request(os.environ)``.  The return
            value will be preserved.
            """
            # @@: In Python 2.5, something usable with with: should also
            # be added.
            try:
                old_conn = self.threadingLocal.connection
                old_conn_is_threading = True
            except AttributeError:
                old_conn = self.processConnection
                old_conn_is_threading = False
            if isinstance(old_conn, string_type):
                old_conn = connectionForURI(old_conn)
            conn = old_conn.transaction()
            if old_conn_is_threading:
                self.threadConnection = conn
            else:
                self.processConnection = conn
            try:
                try:
                    value = func(*args, **kw)
                except Exception:
                    conn.rollback()
                    raise
                else:
                    conn.commit(close=True)
                    return value
            finally:
                if old_conn_is_threading:
                    self.threadConnection = old_conn
                else:
                    self.processConnection = old_conn

        def _set_threadConnection(self, value):
            self.threadingLocal.connection = value

        def _get_threadConnection(self):
            return self.threadingLocal.connection

        def _del_threadConnection(self):
            del self.threadingLocal.connection

        threadConnection = property(_get_threadConnection,
                                    _set_threadConnection,
                                    _del_threadConnection)

    class ConnectionURIOpener(object):

        def __init__(self):
            self.schemeBuilders = {}
            self.instanceNames = {}
            self.cachedURIs = {}

        def registerConnection(self, schemes, builder):
            for uriScheme in schemes:
                assert uriScheme not in self.schemeBuilders \
                    or self.schemeBuilders[uriScheme] is builder, \
                    "A driver has already been registered " \
                    "for the URI scheme %s" % uriScheme
                self.schemeBuilders[uriScheme] = builder

        def registerConnectionInstance(self, inst):
            if inst.name:
                assert (inst.name not in self.instanceNames
                        or self.instanceNames[inst.name] is cls  # noqa
                        ), ("A instance has already been registered "
                            "with the name %s" % inst.name)
                assert inst.name.find(':') == -1, \
                    "You cannot include ':' " \
                    "in your class names (%r)" % cls.name  # noqa
                self.instanceNames[inst.name] = inst

        def connectionForURI(self, uri, oldUri=False, **args):
            if args:
                if '?' not in uri:
                    uri += '?' + urlencode(args)
                else:
                    uri += '&' + urlencode(args)
            if uri in self.cachedURIs:
                return self.cachedURIs[uri]
            if uri.find(':') != -1:
                scheme, rest = uri.split(':', 1)
                connCls = self.dbConnectionForScheme(scheme)
                if oldUri:
                    conn = connCls.connectionFromOldURI(uri)
                else:
                    conn = connCls.connectionFromURI(uri)
            else:
                # We just have a name, not a URI
                assert uri in self.instanceNames, \
                    "No SQLObject driver exists under the name %s" % uri
                conn = self.instanceNames[uri]
            # @@: Do we care if we clobber another connection?
            self.cachedURIs[uri] = conn
            return conn

        def dbConnectionForScheme(self, scheme):
            assert scheme in self.schemeBuilders, (
                "No SQLObject driver exists for %s (only %s)" % (
                    scheme,
                    ', '.join(self.schemeBuilders.keys())))
            return self.schemeBuilders[scheme]()

    TheURIOpener = ConnectionURIOpener()

    registerConnection = TheURIOpener.registerConnection
    registerConnectionInstance = TheURIOpener.registerConnectionInstance
    connectionForURI = TheURIOpener.connectionForURI
    dbConnectionForScheme = TheURIOpener.dbConnectionForScheme

    # Register DB URI schemas -- do import for side effects
    # noqa is a directive for flake8 to ignore seemingly unused imports
    from . import firebird  # noqa
    from . import maxdb  # noqa
    from . import mssql  # noqa
    from . import mysql  # noqa
    from . import postgres  # noqa
    from . import sqlite  # noqa
    from . import sybase  # noqa