def FROM(self, tr, *pattern, seed=Map()): # seed is immutable
"""Yields bindings that match PATTERN"""
assert len(pattern) == len(self._items), "invalid item count"
# TODO: validate that pattern does not have variables named
# `alive?` or `changeid`.
def bind(pattern, binding):
for item in pattern:
if isinstance(item, Variable):
yield binding[item.name]
else:
yield item
# The complexity really depends on the pattern. A pattern
# only made of variables will scan the whole database. In
# practice, the user will seldom do time traveling queries, so
# it should rarely hit this code path.
pattern = list(pattern) + [
nstore.var('alive?'), nstore.var('changeid')
]
bindings = self._tuples.FROM(tr, *pattern, seed=seed)
for binding in bindings:
if not binding['alive?']:
# The associated tuple is dead, so the bindings are
# not valid in all cases.
continue
elif self.ask(self, *bind(pattern, binding)):
# The bound pattern exist, so the bindings are valid
binding = binding.delete('alive?')
binding = binding.delete('changeid')
yield binding
else:
continue
def change_message(self, tr, changeid, message):
# Remove existing message if any
bindings = self._changes.FROM(tr, changeid, 'message',
nstore.var('message'))
for binding in bindings:
self._changes.delete(tr, changeid, 'message', binding['message'])
# add message
self._changes.add(tr, changeid, 'message', message)
def ask(self, tr, *items):
assert len(items) == len(self._items), "Incorrect count of ITEMS"
# Complexity is O(n), where n is the number of times the exact
# same ITEMS was added and deleted. In pratice, n=0, n=1 or
# n=2, and of course it always possible that it is more...
bindings = self._tuples.FROM(tr, *items, nstore.var('alive?'),
nstore.var('changeid'))
found = False
significance_max = fdb.tuple.Versionstamp(b'\x00' * 10)
for binding in bindings:
changeid = binding['changeid']
significance = self._changes.FROM(tr, changeid, 'significance',
nstore.var('significance'))
significance = next(significance)
significance = significance['significance']
if (significance
is not None) and (significance > significance_max):
found = binding['alive?']
return found