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Add some docstrings and comments near get_cached_instance.

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voussoir 2020-04-03 12:33:19 -07:00
parent 18c2f0dc78
commit 545ea62818
1 changed files with 25 additions and 0 deletions
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25
etiquette/photodb.py
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@ -1485,6 +1485,15 @@ class PhotoDB(
return self._cached_frozen_children
def get_cached_instance(self, thing_type, db_row):
'''
Check if there is already an instance in the cache and return that.
Otherwise, a new instance is created, cached, and returned.
Note that in order to call this method you have to already have a
db_row which means performing some select. If you only have the ID,
use get_thing_by_id, as there may already be a cached instance to save
you the select.
'''
thing_map = _THING_CLASSES[thing_type]
thing_table = thing_map['table']
@ -1528,10 +1537,20 @@ class PhotoDB(
yield thing
def get_thing_by_id(self, thing_type, thing_id):
'''
This method will first check the cache to see if there is already an
instance with that ID, in which case we don't need to perform any SQL
select. If it is not in the cache, then a new instance is created,
cached, and returned.
'''
thing_map = _THING_CLASSES[thing_type]
thing_class = thing_map['class']
if isinstance(thing_id, thing_class):
# This could be used to check if your old reference to an object is
# still in the cache, or re-select it from the db to make sure it
# still exists and re-cache.
# Probably an uncommon need but... no harm I think.
thing_id = thing_id.id
thing_cache = self.caches[thing_type]
@ -1563,6 +1582,12 @@ class PhotoDB(
yield thing
def get_things_by_id(self, thing_type, thing_ids):
'''
Given multiple IDs, this method will find which ones are in the cache
and which ones need to be selected from the db.
This is better than calling get_thing_by_id in a loop because we can
use a single SQL select to get batches of up to 999 items.
'''
thing_map = _THING_CLASSES[thing_type]
thing_class = thing_map['class']
thing_cache = self.caches[thing_type]