dbapi.py
author Aurelien Campeas <aurelien.campeas@logilab.fr>
Fri, 02 Apr 2010 13:53:27 +0200
branchstable
changeset 5137 efc280ad9898
parent 5100 04c71ebf38a5
child 5174 78438ad513ca
child 5307 228932b4f8c5
permissions -rw-r--r--
[doc/book] enhance i18n section #656191

"""DB-API 2.0 compliant module

Take a look at http://www.python.org/peps/pep-0249.html

(most parts of this document are reported here in docstrings)

:organization: Logilab
:copyright: 2001-2010 LOGILAB S.A. (Paris, FRANCE), license is LGPL v2.
:contact: http://www.logilab.fr/ -- mailto:contact@logilab.fr
:license: GNU Lesser General Public License, v2.1 - http://www.gnu.org/licenses
"""
__docformat__ = "restructuredtext en"

from logging import getLogger
from time import time, clock
from itertools import count

from logilab.common.logging_ext import set_log_methods
from logilab.common.decorators import monkeypatch
from logilab.common.deprecation import deprecated

from cubicweb import ETYPE_NAME_MAP, ConnectionError, cwvreg, cwconfig
from cubicweb.req import RequestSessionBase


_MARKER = object()

def _fake_property_value(self, name):
    try:
        return super(DBAPIRequest, self).property_value(name)
    except KeyError:
        return ''

def multiple_connections_fix():
    """some monkey patching necessary when an application has to deal with
    several connections to different repositories. It tries to hide buggy class
    attributes since classes are not designed to be shared among multiple
    registries.
    """
    defaultcls = cwvreg.VRegistry.REGISTRY_FACTORY[None]

    etypescls = cwvreg.VRegistry.REGISTRY_FACTORY['etypes']
    orig_etype_class = etypescls.orig_etype_class = etypescls.etype_class
    @monkeypatch(defaultcls)
    def etype_class(self, etype):
        """return an entity class for the given entity type.
        Try to find out a specific class for this kind of entity or
        default to a dump of the class registered for 'Any'
        """
        usercls = orig_etype_class(self, etype)
        if etype == 'Any':
            return usercls
        usercls.e_schema = self.schema.eschema(etype)
        return usercls

def multiple_connections_unfix():
    etypescls = cwvreg.VRegistry.REGISTRY_FACTORY['etypes']
    etypescls.etype_class = etypescls.orig_etype_class


class ConnectionProperties(object):
    def __init__(self, cnxtype=None, lang=None, close=True, log=False):
        self.cnxtype = cnxtype or 'pyro'
        self.lang = lang
        self.log_queries = log
        self.close_on_del = close


def get_repository(method, database=None, config=None, vreg=None):
    """get a proxy object to the CubicWeb repository, using a specific RPC method.

    Only 'in-memory' and 'pyro' are supported for now. Either vreg or config
    argument should be given
    """
    assert method in ('pyro', 'inmemory')
    assert vreg or config
    if vreg and not config:
        config = vreg.config
    if method == 'inmemory':
        # get local access to the repository
        from cubicweb.server.repository import Repository
        return Repository(config, vreg=vreg)
    else: # method == 'pyro'
        # resolve the Pyro object
        from logilab.common.pyro_ext import ns_get_proxy
        try:
            return ns_get_proxy(database,
                                defaultnsgroup=config['pyro-ns-group'],
                                nshost=config['pyro-ns-host'])
        except Exception, ex:
            raise ConnectionError(str(ex))

def repo_connect(repo, login, **kwargs):
    """Constructor to create a new connection to the CubicWeb repository.

    Returns a Connection instance.
    """
    if not 'cnxprops' in kwargs:
        kwargs['cnxprops'] = ConnectionProperties('inmemory')
    cnxid = repo.connect(unicode(login), **kwargs)
    cnx = Connection(repo, cnxid, kwargs['cnxprops'])
    if kwargs['cnxprops'].cnxtype == 'inmemory':
        cnx.vreg = repo.vreg
    return cnx

def connect(database=None, login=None, host=None, group=None,
            cnxprops=None, setvreg=True, mulcnx=True, initlog=True, **kwargs):
    """Constructor for creating a connection to the CubicWeb repository.
    Returns a Connection object.

    When method is 'pyro', setvreg is True, try to deal with connections to
    differents instances in the same process unless specified otherwise by
    setting the mulcnx to False.
    """
    config = cwconfig.CubicWebNoAppConfiguration()
    if host:
        config.global_set_option('pyro-ns-host', host)
    if group:
        config.global_set_option('pyro-ns-group', group)
    cnxprops = cnxprops or ConnectionProperties()
    method = cnxprops.cnxtype
    repo = get_repository(method, database, config=config)
    if method == 'inmemory':
        vreg = repo.vreg
    elif setvreg:
        if mulcnx:
            multiple_connections_fix()
        vreg = cwvreg.CubicWebVRegistry(config, initlog=initlog)
        schema = repo.get_schema()
        for oldetype, newetype in ETYPE_NAME_MAP.items():
            if oldetype in schema:
                print 'aliasing', newetype, 'to', oldetype
                schema._entities[newetype] = schema._entities[oldetype]
        vreg.set_schema(schema)
    else:
        vreg = None
    cnx = repo_connect(repo, login, cnxprops=cnxprops, **kwargs)
    cnx.vreg = vreg
    return cnx

def in_memory_cnx(config, login, **kwargs):
    """usefull method for testing and scripting to get a dbapi.Connection
    object connected to an in-memory repository instance
    """
    if isinstance(config, cwvreg.CubicWebVRegistry):
        vreg = config
        config = None
    else:
        vreg = None
    # get local access to the repository
    repo = get_repository('inmemory', config=config, vreg=vreg)
    # connection to the CubicWeb repository
    cnxprops = ConnectionProperties('inmemory')
    cnx = repo_connect(repo, login, cnxprops=cnxprops, **kwargs)
    return repo, cnx


class DBAPIRequest(RequestSessionBase):

    def __init__(self, vreg, cnx=None):
        super(DBAPIRequest, self).__init__(vreg)
        try:
            # no vreg or config which doesn't handle translations
            self.translations = vreg.config.translations
        except AttributeError:
            self.translations = {}
        self.set_default_language(vreg)
        # cache entities built during the request
        self._eid_cache = {}
        # these args are initialized after a connection is
        # established
        self.cnx = None   # connection associated to the request
        self._user = None # request's user, set at authentication
        if cnx is not None:
            self.set_connection(cnx)

    def base_url(self):
        return self.vreg.config['base-url']

    def from_controller(self):
        return 'view'

    def set_connection(self, cnx, user=None):
        """method called by the session handler when the user is authenticated
        or an anonymous connection is open
        """
        self.cnx = cnx
        self.cursor = cnx.cursor(self)
        self.set_user(user)

    def set_default_language(self, vreg):
        try:
            self.lang = vreg.property_value('ui.language')
        except: # property may not be registered
            self.lang = 'en'
        # use req.__ to translate a message without registering it to the catalog
        try:
            gettext, pgettext = self.translations[self.lang]
            self._ = self.__ = gettext
            self.pgettext = pgettext
        except KeyError:
            # this occurs usually during test execution
            self._ = self.__ = unicode
            self.pgettext = lambda x, y: y
        self.debug('request default language: %s', self.lang)

    def describe(self, eid):
        """return a tuple (type, sourceuri, extid) for the entity with id <eid>"""
        return self.cnx.describe(eid)

    def source_defs(self):
        """return the definition of sources used by the repository."""
        return self.cnx.source_defs()

    # entities cache management ###############################################

    def entity_cache(self, eid):
        return self._eid_cache[eid]

    def set_entity_cache(self, entity):
        self._eid_cache[entity.eid] = entity

    def cached_entities(self):
        return self._eid_cache.values()

    def drop_entity_cache(self, eid=None):
        if eid is None:
            self._eid_cache = {}
        else:
            del self._eid_cache[eid]

    # low level session data management #######################################

    def session_data(self):
        """return a dictionnary containing session data"""
        return self.cnx.session_data()

    def get_session_data(self, key, default=None, pop=False):
        """return value associated to `key` in session data"""
        if self.cnx is None:
            return default # before the connection has been established
        return self.cnx.get_session_data(key, default, pop)

    def set_session_data(self, key, value):
        """set value associated to `key` in session data"""
        return self.cnx.set_session_data(key, value)

    def del_session_data(self, key):
        """remove value associated to `key` in session data"""
        return self.cnx.del_session_data(key)

    def get_shared_data(self, key, default=None, pop=False):
        """return value associated to `key` in shared data"""
        return self.cnx.get_shared_data(key, default, pop)

    def set_shared_data(self, key, value, querydata=False):
        """set value associated to `key` in shared data

        if `querydata` is true, the value will be added to the repository
        session's query data which are cleared on commit/rollback of the current
        transaction, and won't be available through the connexion, only on the
        repository side.
        """
        return self.cnx.set_shared_data(key, value, querydata)

    # server session compat layer #############################################

    def hijack_user(self, user):
        """return a fake request/session using specified user"""
        req = DBAPIRequest(self.vreg)
        req.set_connection(self.cnx, user)
        return req

    @property
    def user(self):
        if self._user is None and self.cnx:
            self.set_user(self.cnx.user(self, {'lang': self.lang}))
        return self._user

    def set_user(self, user):
        self._user = user
        if user:
            self.set_entity_cache(user)

    def execute(self, *args, **kwargs):
        """Session interface compatibility"""
        return self.cursor.execute(*args, **kwargs)

set_log_methods(DBAPIRequest, getLogger('cubicweb.dbapi'))


# exceptions ##################################################################

class ProgrammingError(Exception): #DatabaseError):
    """Exception raised for errors that are related to the database's operation
    and not necessarily under the control of the programmer, e.g. an unexpected
    disconnect occurs, the data source name is not found, a transaction could
    not be processed, a memory allocation error occurred during processing,
    etc.
    """

# module level objects ########################################################


apilevel = '2.0'

"""Integer constant stating the level of thread safety the interface supports.
Possible values are:

                0     Threads may not share the module.
                1     Threads may share the module, but not connections.
                2     Threads may share the module and connections.
                3     Threads may share the module, connections and
                      cursors.

Sharing in the above context means that two threads may use a resource without
wrapping it using a mutex semaphore to implement resource locking. Note that
you cannot always make external resources thread safe by managing access using
a mutex: the resource may rely on global variables or other external sources
that are beyond your control.
"""
threadsafety = 1

"""String constant stating the type of parameter marker formatting expected by
the interface. Possible values are :

                'qmark'         Question mark style,
                                e.g. '...WHERE name=?'
                'numeric'       Numeric, positional style,
                                e.g. '...WHERE name=:1'
                'named'         Named style,
                                e.g. '...WHERE name=:name'
                'format'        ANSI C printf format codes,
                                e.g. '...WHERE name=%s'
                'pyformat'      Python extended format codes,
                                e.g. '...WHERE name=%(name)s'
"""
paramstyle = 'pyformat'


# connection object ###########################################################

class Connection(object):
    """DB-API 2.0 compatible Connection object for CubicWeb
    """
    # make exceptions available through the connection object
    ProgrammingError = ProgrammingError

    def __init__(self, repo, cnxid, cnxprops=None):
        self._repo = repo
        self.sessionid = cnxid
        self._close_on_del = getattr(cnxprops, 'close_on_del', True)
        self._cnxtype = getattr(cnxprops, 'cnxtype', 'pyro')
        self._closed = None
        if cnxprops and cnxprops.log_queries:
            self.executed_queries = []
            self.cursor_class = LogCursor
        else:
            self.cursor_class = Cursor
        self.anonymous_connection = False
        self.vreg = None
        # session's data
        self.data = {}

    def __repr__(self):
        if self.anonymous_connection:
            return '<Connection %s (anonymous)>' % self.sessionid
        return '<Connection %s>' % self.sessionid

    def __enter__(self):
        return self.cursor()

    def __exit__(self, exc_type, exc_val, exc_tb):
        if exc_type is None:
            self.commit()
        else:
            self.rollback()
            return False #propagate the exception

    def request(self):
        return DBAPIRequest(self.vreg, self)

    def session_data(self):
        """return a dictionnary containing session data"""
        return self.data

    def get_session_data(self, key, default=None, pop=False):
        """return value associated to `key` in session data"""
        if pop:
            return self.data.pop(key, default)
        else:
            return self.data.get(key, default)

    def set_session_data(self, key, value):
        """set value associated to `key` in session data"""
        self.data[key] = value

    def del_session_data(self, key):
        """remove value associated to `key` in session data"""
        try:
            del self.data[key]
        except KeyError:
            pass

    def check(self):
        """raise `BadConnectionId` if the connection is no more valid"""
        if self._closed is not None:
            raise ProgrammingError('Closed connection')
        self._repo.check_session(self.sessionid)

    def set_session_props(self, **props):
        """raise `BadConnectionId` if the connection is no more valid"""
        if self._closed is not None:
            raise ProgrammingError('Closed connection')
        self._repo.set_session_props(self.sessionid, props)

    def get_shared_data(self, key, default=None, pop=False):
        """return value associated to `key` in shared data"""
        if self._closed is not None:
            raise ProgrammingError('Closed connection')
        return self._repo.get_shared_data(self.sessionid, key, default, pop)

    def set_shared_data(self, key, value, querydata=False):
        """set value associated to `key` in shared data

        if `querydata` is true, the value will be added to the repository
        session's query data which are cleared on commit/rollback of the current
        transaction, and won't be available through the connexion, only on the
        repository side.
        """
        if self._closed is not None:
            raise ProgrammingError('Closed connection')
        return self._repo.set_shared_data(self.sessionid, key, value, querydata)

    def get_schema(self):
        """Return the schema currently used by the repository.

        This is NOT part of the DB-API.
        """
        if self._closed is not None:
            raise ProgrammingError('Closed connection')
        return self._repo.get_schema()

    def load_appobjects(self, cubes=_MARKER, subpath=None, expand=True,
                        force_reload=None):
        config = self.vreg.config
        if cubes is _MARKER:
            cubes = self._repo.get_cubes()
        elif cubes is None:
            cubes = ()
        else:
            if not isinstance(cubes, (list, tuple)):
                cubes = (cubes,)
            if expand:
                cubes = config.expand_cubes(cubes)
        if subpath is None:
            subpath = esubpath = ('entities', 'views')
        else:
            esubpath = subpath
        if 'views' in subpath:
            esubpath = list(subpath)
            esubpath.remove('views')
            esubpath.append('web/views')
        cubes = reversed([config.cube_dir(p) for p in cubes])
        vpath = config.build_vregistry_path(cubes, evobjpath=esubpath,
                                            tvobjpath=subpath)
        self.vreg.register_objects(vpath, force_reload)
        if self._cnxtype == 'inmemory':
            # should reinit hooks manager as well
            hm, config = self._repo.hm, self._repo.config
            hm.set_schema(hm.schema) # reset structure
            hm.register_system_hooks(config)
            # instance specific hooks
            if self._repo.config.instance_hooks:
                hm.register_hooks(config.load_hooks(self.vreg))

    load_vobjects = deprecated()(load_appobjects)

    def use_web_compatible_requests(self, baseurl, sitetitle=None):
        """monkey patch DBAPIRequest to fake a cw.web.request, so you should
        able to call html views using rset from a simple dbapi connection.

        You should call `load_appobjects` at some point to register those views.
        """
        from cubicweb.web.request import CubicWebRequestBase as cwrb
        DBAPIRequest.build_ajax_replace_url = cwrb.build_ajax_replace_url.im_func
        DBAPIRequest.list_form_param = cwrb.list_form_param.im_func
        DBAPIRequest.property_value = _fake_property_value
        DBAPIRequest.next_tabindex = count().next
        DBAPIRequest.form = {}
        DBAPIRequest.data = {}
        fake = lambda *args, **kwargs: None
        DBAPIRequest.relative_path = fake
        DBAPIRequest.url = fake
        DBAPIRequest.next_tabindex = fake
        DBAPIRequest.get_page_data = fake
        DBAPIRequest.set_page_data = fake
        DBAPIRequest.add_js = fake #cwrb.add_js.im_func
        DBAPIRequest.add_css = fake #cwrb.add_css.im_func
        # XXX could ask the repo for it's base-url configuration
        self.vreg.config.set_option('base-url', baseurl)
        # XXX why is this needed? if really needed, could be fetched by a query
        if sitetitle is not None:
            self.vreg['propertydefs']['ui.site-title'] = {'default': sitetitle}

    def source_defs(self):
        """Return the definition of sources used by the repository.

        This is NOT part of the DB-API.
        """
        if self._closed is not None:
            raise ProgrammingError('Closed connection')
        return self._repo.source_defs()

    def user(self, req=None, props=None):
        """return the User object associated to this connection"""
        # cnx validity is checked by the call to .user_info
        if self._closed is not None:
            raise ProgrammingError('Closed connection')
        eid, login, groups, properties = self._repo.user_info(self.sessionid,
                                                              props)
        if req is None:
            req = self.request()
        rset = req.eid_rset(eid, 'CWUser')
        user = self.vreg['etypes'].etype_class('CWUser')(req, rset, row=0,
                                                         groups=groups,
                                                         properties=properties)
        user['login'] = login # cache login
        return user

    def __del__(self):
        """close the remote connection if necessary"""
        if self._closed is None and self._close_on_del:
            try:
                self.close()
            except:
                pass

    def describe(self, eid):
        if self._closed is not None:
            raise ProgrammingError('Closed connection')
        return self._repo.describe(self.sessionid, eid)

    def close(self):
        """Close the connection now (rather than whenever __del__ is called).

        The connection will be unusable from this point forward; an Error (or
        subclass) exception will be raised if any operation is attempted with
        the connection. The same applies to all cursor objects trying to use the
        connection.  Note that closing a connection without committing the
        changes first will cause an implicit rollback to be performed.
        """
        if self._closed:
            raise ProgrammingError('Connection is already closed')
        self._repo.close(self.sessionid)
        del self._repo # necessary for proper garbage collection
        self._closed = 1

    def commit(self):
        """Commit pending transaction for this connection to the repository.

        may raises `Unauthorized` or `ValidationError` if we attempted to do
        something we're not allowed to for security or integrity reason.

        If the transaction is undoable, a transaction id will be returned.
        """
        if not self._closed is None:
            raise ProgrammingError('Connection is already closed')
        return self._repo.commit(self.sessionid)

    def rollback(self):
        """This method is optional since not all databases provide transaction
        support.

        In case a database does provide transactions this method causes the the
        database to roll back to the start of any pending transaction.  Closing
        a connection without committing the changes first will cause an implicit
        rollback to be performed.
        """
        if not self._closed is None:
            raise ProgrammingError('Connection is already closed')
        self._repo.rollback(self.sessionid)

    def cursor(self, req=None):
        """Return a new Cursor Object using the connection.  If the database
        does not provide a direct cursor concept, the module will have to
        emulate cursors using other means to the extent needed by this
        specification.
        """
        if self._closed is not None:
            raise ProgrammingError('Can\'t get cursor on closed connection')
        if req is None:
            req = self.request()
        return self.cursor_class(self, self._repo, req=req)

    # undo support ############################################################

    def undoable_transactions(self, ueid=None, req=None, **actionfilters):
        """Return a list of undoable transaction objects by the connection's
        user, ordered by descendant transaction time.

        Managers may filter according to user (eid) who has done the transaction
        using the `ueid` argument. Others will only see their own transactions.

        Additional filtering capabilities is provided by using the following
        named arguments:

        * `etype` to get only transactions creating/updating/deleting entities
          of the given type

        * `eid` to get only transactions applied to entity of the given eid

        * `action` to get only transactions doing the given action (action in
          'C', 'U', 'D', 'A', 'R'). If `etype`, action can only be 'C', 'U' or
          'D'.

        * `public`: when additional filtering is provided, their are by default
          only searched in 'public' actions, unless a `public` argument is given
          and set to false.
        """
        txinfos = self._repo.undoable_transactions(self.sessionid, ueid,
                                                   **actionfilters)
        if req is None:
            req = self.request()
        for txinfo in txinfos:
            txinfo.req = req
        return txinfos

    def transaction_info(self, txuuid, req=None):
        """Return transaction object for the given uid.

        raise `NoSuchTransaction` if not found or if session's user is not
        allowed (eg not in managers group and the transaction doesn't belong to
        him).
        """
        txinfo = self._repo.transaction_info(self.sessionid, txuuid)
        if req is None:
            req = self.request()
        txinfo.req = req
        return txinfo

    def transaction_actions(self, txuuid, public=True):
        """Return an ordered list of action effectued during that transaction.

        If public is true, return only 'public' actions, eg not ones triggered
        under the cover by hooks, else return all actions.

        raise `NoSuchTransaction` if the transaction is not found or if
        session's user is not allowed (eg not in managers group and the
        transaction doesn't belong to him).
        """
        return self._repo.transaction_actions(self.sessionid, txuuid, public)

    def undo_transaction(self, txuuid):
        """Undo the given transaction. Return potential restoration errors.

        raise `NoSuchTransaction` if not found or if session's user is not
        allowed (eg not in managers group and the transaction doesn't belong to
        him).
        """
        return self._repo.undo_transaction(self.sessionid, txuuid)


# cursor object ###############################################################

class Cursor(object):
    """These objects represent a database cursor, which is used to manage the
    context of a fetch operation. Cursors created from the same connection are
    not isolated, i.e., any changes done to the database by a cursor are
    immediately visible by the other cursors. Cursors created from different
    connections can or can not be isolated, depending on how the transaction
    support is implemented (see also the connection's rollback() and commit()
    methods.)
    """

    def __init__(self, connection, repo, req=None):
        """This read-only attribute return a reference to the Connection
        object on which the cursor was created.
        """
        self.connection = connection
        """optionnal issuing request instance"""
        self.req = req

        """This read/write attribute specifies the number of rows to fetch at a
        time with fetchmany(). It defaults to 1 meaning to fetch a single row
        at a time.

        Implementations must observe this value with respect to the fetchmany()
        method, but are free to interact with the database a single row at a
        time. It may also be used in the implementation of executemany().
        """
        self.arraysize = 1

        self._repo = repo
        self._sessid = connection.sessionid
        self._res = None
        self._closed = None
        self._index = 0


    def close(self):
        """Close the cursor now (rather than whenever __del__ is called).  The
        cursor will be unusable from this point forward; an Error (or subclass)
        exception will be raised if any operation is attempted with the cursor.
        """
        self._closed = True


    def execute(self, operation, parameters=None, eid_key=None, build_descr=True):
        """Prepare and execute a database operation (query or command).
        Parameters may be provided as sequence or mapping and will be bound to
        variables in the operation.  Variables are specified in a
        database-specific notation (see the module's paramstyle attribute for
        details).

        A reference to the operation will be retained by the cursor.  If the
        same operation object is passed in again, then the cursor can optimize
        its behavior.  This is most effective for algorithms where the same
        operation is used, but different parameters are bound to it (many
        times).

        For maximum efficiency when reusing an operation, it is best to use the
        setinputsizes() method to specify the parameter types and sizes ahead
        of time.  It is legal for a parameter to not match the predefined
        information; the implementation should compensate, possibly with a loss
        of efficiency.

        The parameters may also be specified as list of tuples to e.g. insert
        multiple rows in a single operation, but this kind of usage is
        depreciated: executemany() should be used instead.

        Return values are not defined by the DB-API, but this here it returns a
        ResultSet object.
        """
        self._res = rset = self._repo.execute(self._sessid, operation,
                                              parameters, eid_key, build_descr)
        rset.req = self.req
        self._index = 0
        return rset


    def executemany(self, operation, seq_of_parameters):
        """Prepare a database operation (query or command) and then execute it
        against all parameter sequences or mappings found in the sequence
        seq_of_parameters.

        Modules are free to implement this method using multiple calls to the
        execute() method or by using array operations to have the database
        process the sequence as a whole in one call.

        Use of this method for an operation which produces one or more result
        sets constitutes undefined behavior, and the implementation is
        permitted (but not required) to raise an exception when it detects that
        a result set has been created by an invocation of the operation.

        The same comments as for execute() also apply accordingly to this
        method.

        Return values are not defined.
        """
        for parameters in seq_of_parameters:
            self.execute(operation, parameters)
            if self._res.rows is not None:
                self._res = None
                raise ProgrammingError('Operation returned a result set')


    def fetchone(self):
        """Fetch the next row of a query result set, returning a single
        sequence, or None when no more data is available.

        An Error (or subclass) exception is raised if the previous call to
        execute*() did not produce any result set or no call was issued yet.
        """
        if self._res is None:
            raise ProgrammingError('No result set')
        row = self._res.rows[self._index]
        self._index += 1
        return row


    def fetchmany(self, size=None):
        """Fetch the next set of rows of a query result, returning a sequence
        of sequences (e.g. a list of tuples). An empty sequence is returned
        when no more rows are available.

        The number of rows to fetch per call is specified by the parameter.  If
        it is not given, the cursor's arraysize determines the number of rows
        to be fetched. The method should try to fetch as many rows as indicated
        by the size parameter. If this is not possible due to the specified
        number of rows not being available, fewer rows may be returned.

        An Error (or subclass) exception is raised if the previous call to
        execute*() did not produce any result set or no call was issued yet.

        Note there are performance considerations involved with the size
        parameter.  For optimal performance, it is usually best to use the
        arraysize attribute.  If the size parameter is used, then it is best
        for it to retain the same value from one fetchmany() call to the next.
        """
        if self._res is None:
            raise ProgrammingError('No result set')
        if size is None:
            size = self.arraysize
        rows = self._res.rows[self._index:self._index + size]
        self._index += size
        return rows


    def fetchall(self):
        """Fetch all (remaining) rows of a query result, returning them as a
        sequence of sequences (e.g. a list of tuples).  Note that the cursor's
        arraysize attribute can affect the performance of this operation.

        An Error (or subclass) exception is raised if the previous call to
        execute*() did not produce any result set or no call was issued yet.
        """
        if self._res is None:
            raise ProgrammingError('No result set')
        if not self._res.rows:
            return []
        rows = self._res.rows[self._index:]
        self._index = len(self._res)
        return rows


    def setinputsizes(self, sizes):
        """This can be used before a call to execute*() to predefine memory
        areas for the operation's parameters.

        sizes is specified as a sequence -- one item for each input parameter.
        The item should be a Type Object that corresponds to the input that
        will be used, or it should be an integer specifying the maximum length
        of a string parameter.  If the item is None, then no predefined memory
        area will be reserved for that column (this is useful to avoid
        predefined areas for large inputs).

        This method would be used before the execute*() method is invoked.

        Implementations are free to have this method do nothing and users are
        free to not use it.
        """
        pass


    def setoutputsize(self, size, column=None):
        """Set a column buffer size for fetches of large columns (e.g. LONGs,
        BLOBs, etc.).  The column is specified as an index into the result
        sequence.  Not specifying the column will set the default size for all
        large columns in the cursor.

        This method would be used before the execute*() method is invoked.

        Implementations are free to have this method do nothing and users are
        free to not use it.
        """
        pass


class LogCursor(Cursor):
    """override the standard cursor to log executed queries"""

    def execute(self, operation, parameters=None, eid_key=None, build_descr=True):
        """override the standard cursor to log executed queries"""
        tstart, cstart = time(), clock()
        rset = Cursor.execute(self, operation, parameters, eid_key, build_descr)
        self.connection.executed_queries.append((operation, parameters,
                                                 time() - tstart, clock() - cstart))
        return rset