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# Source code for camelot.view.proxy.collection_proxy

    #  ============================================================================
    #
    #  Copyright (C) 2007-2011 Conceptive Engineering bvba. All rights reserved.
    #  www.conceptive.be / project-camelot@conceptive.be
    #
    #  This file is part of the Camelot Library.
    #
    #  This file may be used under the terms of the GNU General Public
    #  License version 2.0 as published by the Free Software Foundation
    #  and appearing in the file license.txt included in the packaging of
    #  this file.  Please review this information to ensure GNU
    #  General Public Licensing requirements will be met.
    #
    #  If you are unsure which license is appropriate for your use, please
    #  visit www.python-camelot.com or contact project-camelot@conceptive.be
    #
    #  This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
    #  WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
    #
    #  For use of this library in commercial applications, please contact
    #  project-camelot@conceptive.be
    #
    #  ============================================================================

    """Proxy representing a collection of entities that live in the model thread.

    The proxy represents them in the gui thread and provides access to the data
    with zero delay.  If the data is not yet present in the proxy, dummy data is
    returned and an update signal is emitted when the correct data is available.
    """

    import logging
    logger = logging.getLogger( 'camelot.view.proxy.collection_proxy' )

    import datetime
    import itertools

    from PyQt4.QtCore import Qt, QThread
    from PyQt4 import QtGui, QtCore

    from camelot.core.utils import is_deleted
    from camelot.core.files.storage import StoredFile
    from camelot.view.art import Icon
    from camelot.view.fifo import Fifo
    from camelot.view.controls import delegates
    from camelot.view.controls.exception import register_exception
    from camelot.view.remote_signals import get_signal_handler
    from camelot.view.model_thread import gui_function, \
                                          model_function, post

    from camelot.core.files.storage import StoredImage

    class ProxyDict(dict):
        """Subclass of dictionary to fool the QVariant object and prevent
        it from converting dictionary keys to whatever Qt object, but keep
        everything python"""
        pass

    class DelayedProxy( object ):
        """A proxy object needs to be constructed within the GUI thread. Construct
        a delayed proxy when the construction of a proxy is needed within the Model
        thread.  On first occasion the delayed proxy will be converted to a real
        proxy within the GUI thread
        """

        @model_function
        def __init__( self, admin, collection_getter, columns_getter ):
            self._admin = admin
            self._collection_getter = collection_getter
            self._columns_getter = columns_getter

        @gui_function
        def __call__( self ):
            return CollectionProxy( self._admin,
                                    self._collection_getter,
                                    self._columns_getter )

        def __unicode__(self):
            collection = self._collection_getter()
            if collection:
                try:
                   return u','.join(list(unicode(o) or '' for o,_i in zip(collection,
                                                                          range(3))))
                except TypeError, e:
                   logger.error( 'could not convert object to unicode', exc_info=e )
            return u''

    @model_function
    def strip_data_from_object( obj, columns ):
        """For every column in columns, get the corresponding value from the
        object.  Getting a value from an object is time consuming, so using
        this function should be minimized.
        :param obj: the object of which to get data
        :param columns: a list of columns for which to get data
        """
        row_data = []

        def create_collection_getter( o, attr ):
            return lambda: getattr( o, attr )

        for _i, col in enumerate( columns ):
            field_attributes = col[1]
            field_value = None
            try:
                getter = field_attributes['getter']
                if field_attributes['python_type'] == list:
                    field_value = DelayedProxy( field_attributes['admin'],
                                                create_collection_getter( obj, col[0] ),
                                                field_attributes['admin'].get_columns )
                else:
                    field_value = getter( obj )
            except (Exception, RuntimeError, TypeError, NameError), e:
                logger.error('ProgrammingError : could not get field %s of object of type %s'%(col[0], obj.__class__.__name__),
                             exc_info=e)
            finally:
                row_data.append( field_value )
        return row_data

    @model_function
    def stripped_data_to_unicode( stripped_data, obj, static_field_attributes, dynamic_field_attributes ):
        """Extract for each field in the row data a 'visible' form of
        data"""

        row_data = []

        for field_data, static_attributes, dynamic_attributes in zip( stripped_data, static_field_attributes, dynamic_field_attributes ):
            unicode_data = u''
            choices = dynamic_attributes.get( 'choices', static_attributes.get('choices', None))
            if 'unicode_format' in static_attributes:
                unicode_format = static_attributes['unicode_format']
                if field_data != None:
                    unicode_data = unicode_format( field_data )
            elif choices:
                unicode_data = field_data
                for key, value in choices:
                    if key == field_data:
                        unicode_data = value
            elif isinstance( field_data, list ):
                unicode_data = u'.'.join( [unicode( e ) for e in field_data] )
            elif isinstance( field_data, datetime.datetime ):
                # datetime should come before date since datetime is a subtype of date
                if field_data.year >= 1900:
                    unicode_data = field_data.strftime( '%d/%m/%Y %H:%M' )
            elif isinstance( field_data, datetime.date ):
                if field_data.year >= 1900:
                    unicode_data = field_data.strftime( '%d/%m/%Y' )
            elif isinstance( field_data, StoredImage):
                unicode_data = field_data.checkout_thumbnail(100, 100)
            elif field_data != None:
                unicode_data = unicode( field_data )
            row_data.append( unicode_data )

        return row_data

    from camelot.view.proxy import ValueLoading

    class EmptyRowData( object ):
        def __getitem__( self, column ):
            return ValueLoading

    empty_row_data = EmptyRowData()

    class SortingRowMapper( dict ):
        """Class mapping rows of a collection 1:1 without sorting
        and filtering, unless a mapping has been defined explicitly"""

        def __getitem__(self, row):
            try:
                return super(SortingRowMapper, self).__getitem__(row)
            except KeyError:
                return row

    class CollectionProxy( QtCore.QAbstractTableModel ):
        """The CollectionProxy contains a limited copy of the data in the actual
        collection, usable for fast visualisation in a QTableView

        the CollectionProxy has some class attributes that can be overwritten when
        subclassing it :

        * header_icon : the icon to be used in the vertical header

        """

        _header_font = QtGui.QApplication.font()
        _header_font_required = QtGui.QApplication.font()
        _header_font_required.setBold( True )

        header_icon = Icon( 'tango/16x16/places/folder.png' )

        item_delegate_changed_signal = QtCore.pyqtSignal()
        row_changed_signal = QtCore.pyqtSignal(int)
        exception_signal = QtCore.pyqtSignal(object)
        rows_removed_signal = QtCore.pyqtSignal()

        @gui_function
        def __init__( self,
                      admin,
                      collection_getter,
                      columns_getter,
                      max_number_of_rows = 10,
                      edits = None,
                      flush_changes = True,
                      cache_collection_proxy = None
                      ):
            """
    :param admin: the admin interface for the items in the collection

    :param collection_getter: a function that takes no arguments and returns
    the collection that will be visualized. This function will be called inside
    the model thread, to prevent delays when this function causes the database
    to be hit.  If the collection is a list, it should not contain any duplicate
    elements.

    :param columns_getter: a function that takes no arguments and returns the
    columns that will be cached in the proxy. This function will be called
    inside the model thread.

    :param cache_collection_proxy: the CollectionProxy on which this CollectionProxy
    will reuse the cache. Passing a cache has the advantage that objects that were
    present in the original cache will remain at the same row in the new cache
    This is used when a form is created from a tableview.  Because between the last
    query of the tableview, and the first of the form, the object might have changed
    position in the query.
    """
            super(CollectionProxy, self).__init__()
            from camelot.view.model_thread import get_model_thread
            self.logger = logging.getLogger(logger.name + '.%s'%id(self))
            self.logger.debug('initialize query table for %s' % (admin.get_verbose_name()))
            self._mutex = QtCore.QMutex()
            self.admin = admin
            self._horizontal_header_height = QtGui.QFontMetrics( self._header_font_required ).height() + 10
            vertical_header_font_height = QtGui.QFontMetrics( self._header_font ).height()
            self._vertical_header_height = vertical_header_font_height * self.admin.lines_per_row + 10
            self.iconSize = QtCore.QSize( vertical_header_font_height,
                                          vertical_header_font_height )
            if self.header_icon:
                self.form_icon = QtCore.QVariant( self.header_icon.getQIcon().pixmap( self.iconSize ) )
            else:
                self.form_icon = QtCore.QVariant()
            self.validator = admin.create_validator( self )
            self._collection_getter = collection_getter
            self.column_count = 0
            self.flush_changes = flush_changes
            self.delegate_manager = None
            self.mt = get_model_thread()
            # Set database connection and load data
            self._rows = 0
            self._columns = []
            self._static_field_attributes = []
            self._max_number_of_rows = max_number_of_rows
            if cache_collection_proxy:
                self.display_cache = cache_collection_proxy.display_cache.shallow_copy( 10 * self.max_number_of_rows )
                self.edit_cache = cache_collection_proxy.edit_cache.shallow_copy( 10 * self.max_number_of_rows )
                self.attributes_cache = cache_collection_proxy.attributes_cache.shallow_copy( 10 * self.max_number_of_rows )
            else:
                self.display_cache = Fifo( 10 * self.max_number_of_rows )
                self.edit_cache = Fifo( 10 * self.max_number_of_rows )
                self.attributes_cache = Fifo( 10 * self.max_number_of_rows )
            # The rows in the table for which a cache refill is under request
            self.rows_under_request = set()
            self._update_requests = list()
            # The rows that have unflushed changes
            self.unflushed_rows = set()
            self._sort_and_filter = SortingRowMapper()
            # Set edits
            self.edits = edits or []
            self.row_changed_signal.connect( self._emit_changes )
            self.rsh = get_signal_handler()
            self.rsh.connect_signals( self )

            def get_columns():
                self._columns = columns_getter()
                self._static_field_attributes = list(self.admin.get_static_field_attributes([c[0] for c in self._columns]))
                return self._columns

            post( get_columns, self.setColumns )
    #    # the initial collection might contain unflushed rows
            post( self._update_unflushed_rows )
    #    # in that way the number of rows is requested as well
            if cache_collection_proxy:
                self.setRowCount( cache_collection_proxy.rowCount() )
            else:
                post( self.getRowCount, self.setRowCount )
            self.logger.debug( 'initialization finished' )

        @property
        def max_number_of_rows(self):
            """The maximum number of rows to be displayed at once"""
            return self._max_number_of_rows

        def get_validator(self):
            return self.validator

        def map_to_source(self, sorted_row_number):
            """Converts a sorted row number to a row number of the source
            collection"""
            return self._sort_and_filter[sorted_row_number]

        @model_function
        def _update_unflushed_rows( self ):
            """Verify all rows to see if some of them should be added to the
            unflushed rows"""
            for i, e in enumerate( self.get_collection() ):
                if hasattr(e, 'id') and not e.id:
                    self.unflushed_rows.add( i )

        def hasUnflushedRows( self ):
            """The model has rows that have not been flushed to the database yet,
            because the row is invalid
            """
            has_unflushed_rows = ( len( self.unflushed_rows ) > 0 )
            self.logger.debug( 'hasUnflushed rows : %s' % has_unflushed_rows )
            return has_unflushed_rows

        @model_function
        def getRowCount( self ):
            # make sure we don't count an object twice if it is twice
            # in the list, since this will drive the cache nuts
            rows = len( set( self.get_collection() ) )
            return rows

        @gui_function
        def revertRow( self, row ):
            def create_refresh_entity( row ):

                @model_function
                def refresh_entity():
                    o = self._get_object( row )
                    self.admin.refresh( o )
                    return row, o

                return refresh_entity

            post( create_refresh_entity( row ), self._revert_row )

        @QtCore.pyqtSlot(tuple)
        @gui_function
        def _revert_row(self, row_and_entity ):
            row, entity = row_and_entity
            self.handleRowUpdate( row )
            self.rsh.sendEntityUpdate( self, entity )

        @gui_function
        def refresh( self ):
            post( self.getRowCount, self._refresh_content )

        @QtCore.pyqtSlot(int)
        @gui_function
        def _refresh_content(self, rows ):
            self.display_cache = Fifo( 10 * self.max_number_of_rows )
            self.edit_cache = Fifo( 10 * self.max_number_of_rows )
            self.attributes_cache = Fifo( 10 * self.max_number_of_rows )
            locker = QtCore.QMutexLocker(self._mutex)
            self.rows_under_request = set()
            self.unflushed_rows = set()
            locker.unlock()
            self.setRowCount( rows )

        def set_collection_getter( self, collection_getter ):
            self.logger.debug('set collection getter')
            self._collection_getter = collection_getter
            self.refresh()

        @model_function
        def get_collection( self ):
            return self._collection_getter()

        @gui_function
        def handleRowUpdate( self, row ):
            """Handles the update of a row when this row might be out of date"""
            self.display_cache.delete_by_row( row )
            self.edit_cache.delete_by_row( row )
            self.attributes_cache.delete_by_row( row )
            self.dataChanged.emit( self.index( row, 0 ),
                                   self.index( row, self.column_count ) )

        @QtCore.pyqtSlot( object, object )
        def handle_entity_update( self, sender, entity ):
            """Handles the entity signal, indicating that the model is out of
            date"""
            self.logger.debug( '%s %s received entity update signal' % \
                         ( self.__class__.__name__, self.admin.get_verbose_name() ) )
            if sender != self:
                try:
                    row = self.display_cache.get_row_by_entity(entity)
                except KeyError:
                    self.logger.debug( 'entity not in cache' )
                    return
                #
                # Because the entity is updated, it might no longer be in our
                # collection, therefore, make sure we don't access the collection
                # to strip data of the entity
                #
                def create_entity_update(row, entity):

                    def entity_update():
                        columns = self.getColumns()
                        self._add_data(columns, row, entity)
                        return row

                    return entity_update

                post(create_entity_update(row, entity), self._emit_changes)
            else:
                self.logger.debug( 'duplicate update' )

        @QtCore.pyqtSlot( object, object )
        def handle_entity_delete( self, sender, entity ):
            """Handles the entity signal, indicating that the model is out of
            date"""
            self.logger.debug( 'received entity delete signal' )
            #
            # simply removing the entity from the collection might have
            # undesirable effects.  eg when a form is pointing to this entity,
            # so instead update the entity
            #
            self.handle_entity_update( sender, entity )

        @QtCore.pyqtSlot( object, object )
        def handle_entity_create( self, sender, entity ):
            """Handles the entity signal, indicating that the model is out of
            date"""
            self.logger.debug( 'received entity create signal' )
            # @todo : decide what to do when a new entity has been created,
            #         probably do nothing
            return

        @QtCore.pyqtSlot(int)
        def setRowCount( self, rows ):
            """Callback method to set the number of rows
            @param rows the new number of rows
            """
            self._rows = rows
            self.layoutChanged.emit()

        def getItemDelegate( self ):
            """:return: a DelegateManager for this model, or None if no DelegateManager yet available
            a DelegateManager will be available once the item_delegate_changed signal has been emitted"""
            self.logger.debug( 'getItemDelegate' )
            return self.delegate_manager

        def getColumns( self ):
            """:return: the columns as set by the setColumns method"""
            return self._columns

        @QtCore.pyqtSlot(object)
        @gui_function
        def setColumns( self, columns ):
            """Callback method to set the columns

            :param columns: a list with fields to be displayed of the form [('field_name', field_attributes), ...] as
            returned by the getColumns method of the ElixirAdmin class
            """
            self.logger.debug( 'setColumns' )
            self.column_count = len( columns )
            self._columns = columns

            delegate_manager = delegates.DelegateManager()
            delegate_manager.set_columns_desc( columns )

            # set a delegate for the vertical header
            delegate_manager.insertColumnDelegate( -1, delegates.PlainTextDelegate(parent = delegate_manager) )

            #
            # this loop can take a while to complete, so processEvents is called regulary
            #
            for i, c in enumerate( columns ):
    #            if i%10==0:
    #                QtCore.QCoreApplication.processEvents(QtCore.QEventLoop.ExcludeSocketNotifiers, 100)
                field_name = c[0]
                self.logger.debug( 'creating delegate for %s' % field_name )
                if 'delegate' in c[1]:
                    try:
                        delegate = c[1]['delegate']( parent = delegate_manager, **c[1] )
                    except Exception, e:
                        logger.error('ProgrammingError : could not create delegate for field %s'%field_name, exc_info=e)
                        delegate = delegates.PlainTextDelegate( parent = delegate_manager, **c[1] )
                    delegate_manager.insertColumnDelegate( i, delegate )
                    continue
                elif c[1]['python_type'] == str:
                    if c[1]['length']:
                        delegate = delegates.PlainTextDelegate( parent = delegate_manager, maxlength = c[1]['length'] )
                        delegate_manager.insertColumnDelegate( i, delegate )
                    else:
                        delegate = delegates.TextEditDelegate( parent = delegate_manager, **c[1] )
                        delegate_manager.insertColumnDelegate( i, delegate )
                else:
                    delegate = delegates.PlainTextDelegate(parent = delegate_manager)
                    delegate_manager.insertColumnDelegate( i, delegate )

            # Only set the delegate manager when it is fully set up
            self.delegate_manager = delegate_manager
            self.item_delegate_changed_signal.emit()
            self.layoutChanged.emit()

        def rowCount( self, index = None ):
            return self._rows

        def columnCount( self, index = None ):
            return self.column_count

        @gui_function
        def headerData( self, section, orientation, role ):
            """In case the columns have not been set yet, don't even try to get
            information out of them
            """
            if orientation == Qt.Horizontal:
                if section >= self.column_count:
                    return QtCore.QAbstractTableModel.headerData( self, section, orientation, role )
                c = self.getColumns()[section]

                if role == Qt.DisplayRole:
                    return QtCore.QVariant( unicode(c[1]['name']) )

                elif role == Qt.FontRole:
                    if ( 'nullable' in c[1] ) and \
                       ( c[1]['nullable'] == False ):
                        return QtCore.QVariant( self._header_font_required )
                    else:
                        return QtCore.QVariant( self._header_font )

                elif role == Qt.SizeHintRole:
                    option = QtGui.QStyleOptionViewItem()
                    if self.delegate_manager:
                        editor_size = self.delegate_manager.sizeHint( option, self.index( 0, section ) )
                    else:
                        editor_size = QtCore.QSize(0, 0)
                    if 'minimal_column_width' in c[1]:
                        minimal_column_width = QtGui.QFontMetrics( self._header_font ).size( Qt.TextSingleLine, 'A' ).width()*c[1]['minimal_column_width']
                    else:
                        minimal_column_width = 100
                    editable = True
                    if 'editable' in c[1]:
                        editable = c[1]['editable']
                    label_size = QtGui.QFontMetrics( self._header_font_required ).size( Qt.TextSingleLine, unicode(c[1]['name']) + ' ' )
                    size = max( minimal_column_width, label_size.width() + 10 )
                    if editable:
                        size = max( size, editor_size.width() )
                    return QtCore.QVariant( QtCore.QSize( size, self._horizontal_header_height ) )
            else:
                if role == Qt.SizeHintRole:
                    if self.header_icon:
                        return QtCore.QVariant( QtCore.QSize( self.iconSize.width() + 10,
                                                              self._vertical_header_height ) )
                    else:
                        # if there is no icon, the line numbers will be displayed, so create some space for those
                        return QtCore.QVariant( QtCore.QSize( QtGui.QFontMetrics( self._header_font ).size( Qt.TextSingleLine, str(self._rows) ).width() + 10, self._vertical_header_height ) )
                if role == Qt.DecorationRole:
                    return self.form_icon
    #      elif role == Qt.DisplayRole:
    #        return QtCore.QVariant()
            return QtCore.QAbstractTableModel.headerData( self, section, orientation, role )

        @gui_function
        def sort( self, column, order ):
            """reimplementation of the QAbstractItemModel its sort function"""

            def create_sort(column, order):

                def sort():
                    unsorted_collection = [(i,o) for i,o in enumerate(self.get_collection())]
                    key = lambda item:getattr(item[1], self._columns[column][0])
                    unsorted_collection.sort(key=key, reverse=order)
                    for j,(i,_o) in enumerate(unsorted_collection):
                        self._sort_and_filter[j] = i
                    return len(unsorted_collection)

                return sort

            post(create_sort(column, order), self._refresh_content)

        @gui_function
        def data( self, index, role ):
            """:return: the data at index for the specified role
            This function will return ValueLoading when the data has not
            yet been fetched from the underlying model.  It will then send
            a request to the model thread to fetch this data.  Once the data
            is readily available, the dataChanged signal will be emitted

            Using Qt.UserRole as a role will return all the field attributes
            of the index.

            Using Qt.UserRole+1 will return the object of which an attribute
            is displayed in that specific cell

            """
            if not index.isValid() or \
               not ( 0 <= index.row() <= self.rowCount( index ) ) or \
               not ( 0 <= index.column() <= self.columnCount( index ) ):
                return QtCore.QVariant()
            if role in (Qt.EditRole, Qt.DisplayRole):
                if role == Qt.EditRole:
                    cache = self.edit_cache
                else:
                    cache = self.display_cache
                data = self._get_row_data( index.row(), cache )
                value = data[index.column()]
                if isinstance( value, DelayedProxy ):
                    value = value()
                    # store the created proxy, to prevent recreation of it
                    # afterwards.
                    data[index.column()] = value
                if isinstance( value, datetime.datetime ):
                    # Putting a python datetime into a QVariant and returning
                    # it to a PyObject seems to be buggy, therefore we chop the
                    # microseconds
                    if value:
                        value = QtCore.QDateTime(value.year, value.month,
                                                 value.day, value.hour,
                                                 value.minute, value.second)
                return QtCore.QVariant( value )
            elif role == Qt.ToolTipRole:
                return QtCore.QVariant(self._get_field_attribute_value(index, 'tooltip'))
            elif role == Qt.BackgroundRole:
                return QtCore.QVariant(self._get_field_attribute_value(index, 'background_color') or QtGui.QColor('White'))
            elif role == Qt.UserRole:
                field_attributes = ProxyDict(self._static_field_attributes[index.column()])
                dynamic_field_attributes = self._get_row_data( index.row(), self.attributes_cache )[index.column()]
                if dynamic_field_attributes != ValueLoading:
                    field_attributes.update( dynamic_field_attributes )
                return QtCore.QVariant(field_attributes)
            elif role == Qt.UserRole + 1:
                try:
                    return QtCore.QVariant( self.edit_cache.get_entity_at_row( index.row() ) )
                except KeyError:
                    return QtCore.QVariant( ValueLoading )
            return QtCore.QVariant()

        def _get_field_attribute_value(self, index, field_attribute):
            """Get the values for the static and the dynamic field attributes at once
            :return: the value of the field attribute"""
            try:
                return self._static_field_attributes[index.column()][field_attribute]
            except KeyError:
                value = self._get_row_data( index.row(), self.attributes_cache )[index.column()]
                if value == ValueLoading:
                    return None
                return value.get(field_attribute, None)

        @model_function
        def _handle_update_requests(self):
            #
            # Copy the update requests and clear the list of requests
            #
            locker = QtCore.QMutexLocker(self._mutex)
            update_requests = [u for u in self._update_requests]
            self._update_requests = []
            locker.unlock()
            #
            # Handle the requests
            #
            return_list = []
            for flushed, row, column, value in update_requests:
                attribute, field_attributes = self.getColumns()[column]

                from sqlalchemy.exc import DatabaseError
                from sqlalchemy import orm
                new_value = value()
                self.logger.debug( 'set data for row %s;col %s' % ( row, column ) )

                if new_value == ValueLoading:
                    return None

                #
                # don't use _get_object, but only update objects which are in the
                # cache, otherwise it is not sure that the object updated is the
                # one that was edited
                #
                o = self.edit_cache.get_entity_at_row( row )
                if not o:
                    # the object might have been deleted from the collection while the editor
                    # was still open
                    self.logger.debug( 'this object is no longer in the collection' )
                    try:
                        self.unflushed_rows.remove( row )
                    except KeyError:
                        pass
                    return

                #
                # the object might have been deleted while an editor was open
                #
                if self.admin.is_deleted( o ):
                    return

                old_value = getattr( o, attribute )
                #
                # When the value is a related object, the related object might have changed
                #
                changed = ( new_value != old_value ) or (
                  field_attributes.get('embedded', False) and \
                  field_attributes.get('target', False))
                #
                # In case the attribute is a OneToMany or ManyToMany, we cannot simply compare the
                # old and new value to know if the object was changed, so we'll
                # consider it changed anyway
                #
                direction = field_attributes.get( 'direction', None )
                if direction in ( orm.interfaces.MANYTOMANY, orm.interfaces.ONETOMANY ):
                    changed = True
                if changed:
                    # update the model
                    model_updated = False
                    try:
                        setattr( o, attribute, new_value )
                        #
                        # setting this attribute, might trigger a default function to return a value,
                        # that was not returned before
                        #
                        self.admin.set_defaults( o, include_nullable_fields=False )
                        model_updated = True
                    except AttributeError, e:
                        self.logger.error( u"Can't set attribute %s to %s" % ( attribute, unicode( new_value ) ), exc_info = e )
                    except TypeError:
                        # type error can be raised in case we try to set to a collection
                        pass
                    if self.flush_changes and self.validator.isValid( row ):
                        # save the state before the update
                        try:
                            self.admin.flush( o )
                        except DatabaseError, e:
                            #@todo: when flushing fails, the object should not be removed from the unflushed rows ??
                            self.logger.error( 'Programming Error, could not flush object', exc_info = e )
                        locker.relock()
                        try:
                            self.unflushed_rows.remove( row )
                        except KeyError:
                            pass
                        locker.unlock()
                        #
                        # we can only track history if the model was updated, and it was
                        # flushed before, otherwise it has no primary key yet
                        #
                        if model_updated and hasattr(o, 'id') and o.id:
                            #
                            # in case of files or relations, we cannot pickle them
                            #
                            if isinstance( old_value, StoredFile ):
                                old_value = old_value.name
                            if not direction:
                                from camelot.model.memento import BeforeUpdate
                                # only register the update when the camelot model is active
                                if hasattr(BeforeUpdate, 'query'):
                                    from camelot.model.authentication import getCurrentAuthentication
                                    history = BeforeUpdate( model = unicode( self.admin.entity.__name__ ),
                                                           primary_key = o.id,
                                                           previous_attributes = {attribute:old_value},
                                                           authentication = getCurrentAuthentication() )

                                    try:
                                        history.flush()
                                    except DatabaseError, e:
                                        self.logger.error( 'Programming Error, could not flush history', exc_info = e )
                    # update the cache
                    self._add_data(self.getColumns(), row, o)
                    #@todo: update should only be sent remotely when flush was done
                    self.rsh.sendEntityUpdate( self, o )
                    for depending_obj in self.admin.get_depending_objects( o ):
                        self.rsh.sendEntityUpdate( self, depending_obj )
                    return_list.append(( ( row, 0 ), ( row, len( self.getColumns() ) ) ))
                elif flushed:
                    locker.relock()
                    self.logger.debug( 'old value equals new value, no need to flush this object' )
                    try:
                        self.unflushed_rows.remove( row )
                    except KeyError:
                        pass
                    locker.unlock()
            return return_list

        def setData( self, index, value, role = Qt.EditRole ):
            """Value should be a function taking no arguments that returns the data to
            be set

            This function will then be called in the model_thread
            """
            #
            # prevent data of being set in rows not actually in this model
            #
            if not index.isValid():
                return False

            if role == Qt.EditRole:

                # if the field is not editable, don't waste any time and get out of here
                # editable should be explicitely True, since the _get_field_attribute_value
                # might return intermediary values such as ValueLoading ??
                if self._get_field_attribute_value(index, 'editable') != True:
                    return

                locker = QtCore.QMutexLocker( self._mutex )
                flushed = ( index.row() not in self.unflushed_rows )
                self.unflushed_rows.add( index.row() )
                self._update_requests.append( (flushed, index.row(), index.column(), value) )
                locker.unlock()
                post( self._handle_update_requests )

            return True

        @QtCore.pyqtSlot(int)
        @gui_function
        def _emit_changes( self, row ):
            if row!=None:
                self.dataChanged.emit( self.index( row, 0 ),
                                       self.index( row, self.column_count ) )

        def flags( self, index ):
            """Returns the item flags for the given index"""
            flags = Qt.ItemIsEnabled | Qt.ItemIsSelectable
            if self._get_field_attribute_value(index, 'editable'):
                flags = flags | Qt.ItemIsEditable
            return flags

        def _add_data(self, columns, row, obj):
            """Add data from object o at a row in the cache
            :param columns: the columns of which to strip data
            :param row: the row in the cache into which to add data
            :param obj: the object from which to strip the data
            """
            if not self.admin.is_deleted( obj ):
                row_data = strip_data_from_object( obj, columns )
                dynamic_field_attributes = list(self.admin.get_dynamic_field_attributes( obj, (c[0] for c in columns)))
                static_field_attributes = self.admin.get_static_field_attributes( (c[0] for c in columns) )
                unicode_row_data = stripped_data_to_unicode( row_data, obj, static_field_attributes, dynamic_field_attributes )
            else:
                row_data = [None] * len(columns)
                dynamic_field_attributes =  [{'editable':False}] * len(columns)
                static_field_attributes = self.admin.get_static_field_attributes( (c[0] for c in columns) )
                unicode_row_data = [u''] * len(columns)
            locker = QtCore.QMutexLocker( self._mutex )
            self.edit_cache.add_data( row, obj, row_data )
            self.display_cache.add_data( row, obj, unicode_row_data )
            self.attributes_cache.add_data(row, obj, dynamic_field_attributes )
            locker.unlock()
            #
            # it might be that the CollectionProxy is deleted on the QT side of
            # the application
            #
            if not is_deleted( self ):
                self.row_changed_signal.emit( row )

        def _skip_row(self, row, obj):
            """:return: True if the object obj is already in the cache, but at a
            different row then row.  If this is the case, this object should not
            be put in the cache at row, and this row should be skipped alltogether.
            """
            try:
                return self.edit_cache.get_row_by_entity(obj)!=row
            except KeyError:
                pass
            return False

        def _offset_and_limit_rows_to_get( self ):
            """From the current set of rows to get, find the first
            continuous range of rows that should be fetched.
            :return: (offset, limit)
            """
            offset, limit, previous_length, i = 0, 0, 0, 0
            #
            # wait for a while until the rows under request don't change any
            # more
            #
            locker = QtCore.QMutexLocker(self._mutex)
            while previous_length != len(self.rows_under_request):
                previous_length = len(self.rows_under_request)
                locker.unlock()
                QThread.msleep(5)
                locker.relock()
            #
            # now filter out all rows that have been put in the cache
            # the gui thread didn't know about
            #
            rows_to_get = self.rows_under_request
            rows_already_there = set()
            for row in rows_to_get:
                if self.edit_cache.has_data_at_row(row):
                    rows_already_there.add(row)
            rows_to_get.difference_update( rows_already_there )
            #
            # see if there is anything left to do
            #
            try:
                if rows_to_get:
                    rows_to_get = list(rows_to_get)
                    locker.unlock()
                    rows_to_get.sort()
                    offset = rows_to_get[0]
                    #
                    # find first discontinuity
                    #
                    for i in range(offset, rows_to_get[-1]+1):
                        if rows_to_get[i-offset] != i:
                            break
                    limit = i - offset + 1
            except IndexError, e:
                logger.error('index error with rows_to_get %s'%unicode(rows_to_get), exc_info=e)
                raise e
            return (offset, limit)

        @model_function
        def _extend_cache( self ):
            """Extend the cache around the rows under request"""
            offset, limit = self._offset_and_limit_rows_to_get()
            if limit:
                columns = self.getColumns()
                collection = self.get_collection()
                skipped_rows = 0
                for i in range(offset, min(offset + limit + 1, self._rows)):
                    object_found = False
                    while not object_found:
                        unsorted_row = self._sort_and_filter[i]
                        obj = collection[unsorted_row+skipped_rows]
                        if self._skip_row(i, obj):
                            skipped_rows = skipped_rows + 1
                        else:
                            self._add_data(columns, i, obj)
                            object_found = True
            return ( offset, limit )

        @model_function
        def _get_object( self, sorted_row_number ):
            """Get the object corresponding to row
            :return: the object at row row or None if the row index is invalid
            """
            try:
                # first try to get the primary key out of the cache, if it's not
                # there, query the collection_getter
                return self.edit_cache.get_entity_at_row( sorted_row_number )
            except KeyError:
                pass
            try:
                return self.get_collection()[self.map_to_source(sorted_row_number)]
            except IndexError:
                pass
            return None

        @QtCore.pyqtSlot(tuple)
        def _cache_extended( self, interval ):
            offset, limit = interval
            locker = QtCore.QMutexLocker(self._mutex)
            self.rows_under_request.difference_update( set( range( offset, offset + limit + 1) ) )
            locker.unlock()

        def _get_row_data( self, row, cache ):
            """Get the data which is to be visualized at a certain row of the
            table, if needed, post a refill request the cache to get the object
            and its neighbours in the cache, meanwhile, return an empty object
            :param row: the row of the table for which to get the data
            :param cache: the cache out of which to get row data
            :return: row_data
            """
            try:
                data = cache.get_data_at_row( row )
                #
                # check if data is None, then the cache was a copy of previous
                # cache, and the data should be refetched
                #
                if data is None:
                    raise KeyError
                return data
            except KeyError:
                if row not in self.rows_under_request:
                    locker = QtCore.QMutexLocker(self._mutex)
                    self.rows_under_request.add( row )
                    locker.unlock()
                    post( self._extend_cache, self._cache_extended )
                return empty_row_data

        @model_function
        def remove( self, o ):
            collection = self.get_collection()
            if o in collection:
                collection.remove( o )
                self._rows -= 1

        @model_function
        def append( self, o ):
            collection = self.get_collection()
            if o not in collection:
                collection.append( o )

        @model_function
        def remove_objects( self, objects_to_remove, delete = True ):
            """
            :param objects_to_remove: a list of objects that need to be removed
            from the collection
            :param delete: True if the objects need to be deleted
            """
            #
            # it might be impossible to determine the depending objects once
            # the object has been removed from the collection
            #
            depending_objects = set( itertools.chain.from_iterable( self.admin.get_depending_objects( o ) for o in objects_to_remove ) )
            for obj in objects_to_remove:
                #
                # We should not update depending objects that have
                # been deleted themselves
                #
                if delete:
                    try:
                        depending_objects.remove( obj )
                    except KeyError:
                        pass
                #
                # if needed, delete the objects
                #
                if delete:
                    self.rsh.sendEntityDelete( self, obj )
                    self.admin.delete( obj )
                    # remove only when delete took place without exception
                    self.remove( obj )
                else:
                    # even if the object is not deleted, it needs to be flushed to make
                    # sure the persisted object is out of the collection as well
                    self.remove( obj )
                    if self.admin.is_persistent( obj ):
                        self.admin.flush( obj )
                #
                # remove the entity from the cache, only if the delete and remove
                # took place without exception
                #
                self.display_cache.delete_by_entity( obj )
                self.attributes_cache.delete_by_entity( obj )
                self.edit_cache.delete_by_entity( obj )
            for depending_obj in depending_objects:
                self.rsh.sendEntityUpdate( self, depending_obj )
            post( self.getRowCount, self._refresh_content )

        @gui_function
        def remove_rows( self, rows, delete = True ):
            """Remove the entity associated with this row from this collection
            @param rows: a list with the numbers of the rows to remove
            @param delete: delete the entity as well

            The rows_removed signal will be emitted when the removal was
            successful, otherwise the exception_signal will be emitted.
            """
            self.logger.debug( 'remove rows' )

            def create_delete_function( rows ):

                def delete_function():
                    """Remove all rows from the underlying collection
                    :return: the number of rows left in the collection"""
                    try:
                        objects_to_remove = [self._get_object( row ) for row in rows]
                        self.remove_objects( objects_to_remove, delete )
                        self.rows_removed_signal.emit()
                    except Exception, exc:
                        exc_info = register_exception( logger,
                                                       'exception while removing rows',
                                                       exc )
                        self.exception_signal.emit( exc_info )

                return delete_function

            post( create_delete_function(rows) )
            return True

        @gui_function
        def copy_row( self, row ):
            """Copy the entity associated with this row to the end of the collection
            :param row: the row number
            """

            def create_copy_function( row ):

                def copy_function():
                    o = self._get_object(row)
                    new_object = self.admin.copy( o )
                    self.append_object(new_object)

                return copy_function

            post( create_copy_function( row ) )
            return True

        @model_function
        def append_object( self, obj ):
            """Append an object to this collection, set the possible defaults and flush
            the object if possible/needed

            :param obj: the object to be added to the collection
            :return: the new number of rows in the collection
            """
            rows = self.rowCount()
            row = max( rows - 1, 0 )
            self.beginInsertRows( QtCore.QModelIndex(), row, row )
            self.append( obj )
            # defaults might depend on object being part of a collection
            self.admin.set_defaults( obj )
            self.unflushed_rows.add( row )
            if self.flush_changes and not len( self.validator.objectValidity( obj ) ):
                self.admin.flush( obj )
                try:
                    self.unflushed_rows.remove( row )
                except KeyError:
                    pass
            for depending_obj in self.admin.get_depending_objects( obj ):
                self.rsh.sendEntityUpdate( self, depending_obj )
    # TODO : it's not because an object is added to this list, that it was created
    # it might as well exist already, eg. manytomany relation
    #      from camelot.model.memento import Create
    #      from camelot.model.authentication import getCurrentAuthentication
    #      history = Create(model=unicode(self.admin.entity.__name__),
    #                       primary_key=o.id,
    #                       authentication = getCurrentAuthentication())
    #      elixir.session.flush([history])
    #      self.rsh.sendEntityCreate(self, o)
            self._rows = rows + 1
            self.endInsertRows()
            return self._rows

        @QtCore.pyqtSlot(object)
        @gui_function
        def append_row( self, object_getter ):
            """
            :param object_getter: a function that returns the object to be put in the
            appended row.
            """

            def create_append_function( getter ):

                def append_function():
                    return self.append_object( getter() )

                return append_function

            post( create_append_function( object_getter ), self._refresh_content )

        @model_function
        def getData( self ):
            """Generator for all the data queried by this proxy"""
            for _i, o in enumerate( self.get_collection() ):
                yield strip_data_from_object( o, self.getColumns() )

        def get_admin( self ):
            """Get the admin object associated with this model"""
            return self.admin

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