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"""Module containing the FIFO cache used in the collection proxy to store
the data that is passed between the model and the gui thread"""
from copy import copy
_fill = object()
_no_data = (None,None)
import six
[docs]class Fifo(object):
"""Fifo, is the actual cache containing a limited set of copies of row data
so the data in Fifo, is always immediately accessible to the gui thread,
with zero delay as you scroll down the table view, Fifo is filled and
refilled with data queried from the database
the cache can be queried either by the row number or by object represented
by the row data.
"""
def __init__(self, max_entries):
""":param max_entries: the maximum entries that will be stored in the
cache, if more data is added, the oldest data gets removed"""
self.max_entries = max_entries
self.entities = []
self.data_by_rows = dict()
self.rows_by_entity = dict()
def __unicode__(self):
return u','.join(six.text_type(e) for e in self.entities)
def __str__(self):
return 'Fifo cache of %s rows'%(len(self.entities))
def __len__(self):
"""The number of rows in the cache"""
return len( self.entities )
[docs] def rows(self):
"""
:return: a interator of the row numbers for which this fifo
had data
"""
return six.iterkeys(self.data_by_rows)
[docs] def shallow_copy(self, max_entries):
"""Copy the cache without the actual data but with the references
to which object is stored in which row"""
new_fifo = Fifo(max_entries)
new_fifo.entities = copy( self.entities )
# None is to distinguish between a list of data and no data
new_fifo.data_by_rows = dict( (row, (entity,None)) for (row, (entity, value)) in six.iteritems(self.data_by_rows) )
new_fifo.rows_by_entity = copy( self.rows_by_entity )
return new_fifo
[docs] def add_data(self, row, entity, value):
"""The entity might already be on another row, and this row
might already contain an entity
:return: a :class:`set` with all the changed columns in the row
"""
old_value = self.delete_by_entity(entity)[1]
self.data_by_rows[row] = (entity, value)
self.rows_by_entity[entity] = row
self.entities.append(entity)
if len(self.entities)>self.max_entries:
entity = self.entities.pop(0)
self.delete_by_entity(entity)
if old_value is None:
# there was no old data, so everything has changed
return set( range( len( value ) ) )
values = six.moves.zip_longest( value, old_value or [], fillvalue = _fill )
return set( i for i,(new,old) in enumerate( values ) if new != old )
[docs] def delete_by_row(self, row):
"""Remove the data and the reference to the object at row"""
(entity, _value_) = self.data_by_rows[row]
del self.data_by_rows[row]
del self.rows_by_entity[entity]
return row
[docs] def delete_by_entity(self, entity):
"""Remove everything in the cache related to an entity instance
returns the row at which the data was stored if the data was in the
cache, return None otherwise"""
row, data = None, _no_data
try:
row = self.rows_by_entity[entity]
data = self.data_by_rows.get( row, _no_data )
del self.data_by_rows[row]
del self.rows_by_entity[entity]
except KeyError:
pass
try:
self.entities.remove(entity)
except ValueError:
pass
return row, data[1]
[docs] def has_data_at_row(self, row):
""":return: True if there is data in the cache for the row, False if
there isn't"""
try:
data = self.get_data_at_row( row )
if data is not None:
return True
except KeyError:
pass
return False
[docs] def get_data_at_row(self, row):
""":return: the data at row"""
return self.data_by_rows[row][1]
[docs] def get_row_by_entity(self, entity):
""":return: the row at which an entity is stored"""
return self.rows_by_entity[entity]
[docs] def get_entity_at_row(self, row):
""":return: the entity that is stored at a row"""
return self.data_by_rows[row][0]