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-rw-r--r--actionview/lib/action_view/renderer/partial_renderer/collection_caching.rb35
1 files changed, 35 insertions, 0 deletions
diff --git a/actionview/lib/action_view/renderer/partial_renderer/collection_caching.rb b/actionview/lib/action_view/renderer/partial_renderer/collection_caching.rb
index 3c10e0452f..5aa6f77902 100644
--- a/actionview/lib/action_view/renderer/partial_renderer/collection_caching.rb
+++ b/actionview/lib/action_view/renderer/partial_renderer/collection_caching.rb
@@ -14,15 +14,35 @@ module ActionView
def cache_collection_render(instrumentation_payload)
return yield unless @options[:cached]
+ # Result is a hash with the key represents the
+ # key used for cache lookup and the value is the item
+ # on which the partial is being rendered
keyed_collection = collection_by_cache_keys
+
+ # Pull all partials from cache
+ # Result is a hash, key matches the entry in
+ # `keyed_collection` where the cache was retrieved and the
+ # value is the value that was present in the cache
cached_partials = collection_cache.read_multi(*keyed_collection.keys)
instrumentation_payload[:cache_hits] = cached_partials.size
+ # Extract the items for the keys that are not found
+ # Set the uncached values to instance variable @collection
+ # which is used by the caller
@collection = keyed_collection.reject { |key, _| cached_partials.key?(key) }.values
+
+ # If all elements are already in cache then
+ # rendered partials will be an empty array
+ #
+ # If the cache is missing elements then
+ # the block will be called against the remaining items
+ # in the @collection.
rendered_partials = @collection.empty? ? [] : yield
index = 0
fetch_or_cache_partial(cached_partials, order_by: keyed_collection.each_key) do
+ # This block is called once
+ # for every cache miss while preserving order.
rendered_partials[index].tap { index += 1 }
end
end
@@ -48,6 +68,21 @@ module ActionView
@digest_path ||= @view.digest_path_from_virtual(@template.virtual_path)
end
+ # `order_by` is an enumerable object containing keys of the cache,
+ # all keys are passed in whether found already or not.
+ #
+ # `cached_partials` is a hash. If the value exists
+ # it represents the rendered partial from the cache
+ # otherwise `Hash#fetch` will take the value of its block.
+ #
+ # This method expects a block that will return the rendered
+ # partial. An example is to render all results
+ # for each element that was not found in the cache and store it as an array.
+ # Order it so that the first empty cache element in `cached_partials`
+ # corresponds to the first element in `rendered_partials`.
+ #
+ # If the partial is not already cached it will also be
+ # written back to the underlying cache store.
def fetch_or_cache_partial(cached_partials, order_by:)
order_by.map do |cache_key|
cached_partials.fetch(cache_key) do