def retreive(self, arg):
"""
Checks the cache for data defined by arg and returns it if it's there
@param arg: same as for Extractor.grab()
@return: data specified by the arg or None if it's a cache miss
"""
# deserialize what's in the DB
countries_raw = list(self.db.countries.find())
cached_countries = [Country.from_json(country) for country in countries_raw]
# let's pick what we need from it
target_countries = []
contains_countries, contains_indicators, contains_years = True, True, True
wanted_countries = set(arg["country_codes"])
for country in cached_countries:
# add the countries we need
if country.code in wanted_countries:
target_countries.append(country)
wanted_countries.remove(country.code)
# now for that country, let's go see if we have the indicators
wanted_indicators = set(arg["indicator_codes"])
for indicator in country.indicators.values():
if indicator.code in wanted_indicators:
wanted_indicators.remove(indicator.code)
# cool, it's here; now let's check for its years
begin_date = indicator.nominal_start
end_date = indicator.nominal_end
interval_satisfied = (arg["start_date"]>=begin_date
and arg["end_date"]<=end_date)
if interval_satisfied: #all past indicators contained years
# now we set the data to be
# only the years that were asked for
indicator = indicator.slice(arg["start_date"], arg["end_date"])
else:
contains_years = False
else: # we don't even want that one
country.indicators.pop(indicator.code)
if len(wanted_indicators)>0: contains_indicators = False
if len(wanted_countries) > 0: # empty
# all countries covered
contains_countries = False
# all 3 conditions must be true, no data can be missing
if contains_countries and contains_indicators and contains_years:
return target_countries
else: # we have a cache miss
return None
