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# frozen_string_literal: true
# Grape helpers for caching.
#
# This module helps introduce standardised caching into the Grape API
# in a similar manner to the standard Grape DSL.
module API
module Helpers
module Caching
# @return [ActiveSupport::Duration]
DEFAULT_EXPIRY = 1.day
# @return [ActiveSupport::Cache::Store]
def cache
Rails.cache
end
# This is functionally equivalent to the standard `#present` used in
# Grape endpoints, but the JSON for the object, or for each object of
# a collection, will be cached.
#
# With a collection all the keys will be fetched in a single call and the
# Entity rendered for those missing from the cache, which are then written
# back into it.
#
# Both the single object, and all objects inside a collection, must respond
# to `#cache_key`.
#
# To override the Grape formatter we return a custom wrapper in
# `Gitlab::Json::PrecompiledJson` which tells the `Gitlab::Json::GrapeFormatter`
# to export the string without conversion.
#
# A cache context can be supplied to add more context to the cache key. This
# defaults to including the `current_user` in every key for safety, unless overridden.
#
# @param obj_or_collection [Object, Enumerable<Object>] the object or objects to render
# @param with [Grape::Entity] the entity to use for rendering
# @param cache_context [Proc] a proc to call for each object to provide more context to the cache key
# @param expires_in [ActiveSupport::Duration, Integer] an expiry time for the cache entry
# @param presenter_args [Hash] keyword arguments to be passed to the entity
# @return [Gitlab::Json::PrecompiledJson]
def present_cached(obj_or_collection, with:, cache_context: -> (_) { current_user.cache_key }, expires_in: DEFAULT_EXPIRY, **presenter_args)
json =
if obj_or_collection.is_a?(Enumerable)
cached_collection(
obj_or_collection,
presenter: with,
presenter_args: presenter_args,
context: cache_context,
expires_in: expires_in
)
else
cached_object(
obj_or_collection,
presenter: with,
presenter_args: presenter_args,
context: cache_context,
expires_in: expires_in
)
end
body Gitlab::Json::PrecompiledJson.new(json)
end
private
# Optionally uses a `Proc` to add context to a cache key
#
# @param object [Object] must respond to #cache_key
# @param context [Proc] a proc that will be called with the object as an argument, and which should return a
# string or array of strings to be combined into the cache key
# @return [String]
def contextual_cache_key(object, context)
return object.cache_key if context.nil?
[object.cache_key, context.call(object)].flatten.join(":")
end
# Used for fetching or rendering a single object
#
# @param object [Object] the object to render
# @param presenter [Grape::Entity]
# @param presenter_args [Hash] keyword arguments to be passed to the entity
# @param context [Proc]
# @param expires_in [ActiveSupport::Duration, Integer] an expiry time for the cache entry
# @return [String]
def cached_object(object, presenter:, presenter_args:, context:, expires_in:)
cache.fetch(contextual_cache_key(object, context), expires_in: expires_in) do
Gitlab::Json.dump(presenter.represent(object, **presenter_args).as_json)
end
end
# Used for fetching or rendering multiple objects
#
# @param objects [Enumerable<Object>] the objects to render
# @param presenter [Grape::Entity]
# @param presenter_args [Hash] keyword arguments to be passed to the entity
# @param context [Proc]
# @param expires_in [ActiveSupport::Duration, Integer] an expiry time for the cache entry
# @return [Array<String>]
def cached_collection(collection, presenter:, presenter_args:, context:, expires_in:)
json = fetch_multi(collection, context: context, expires_in: expires_in) do |obj|
Gitlab::Json.dump(presenter.represent(obj, **presenter_args).as_json)
end
json.values
end
# An adapted version of ActiveSupport::Cache::Store#fetch_multi.
#
# The original method only provides the missing key to the block,
# not the missing object, so we have to create a map of cache keys
# to the objects to allow us to pass the object to the missing value
# block.
#
# The result is that this is functionally identical to `#fetch`.
def fetch_multi(*objs, context:, **kwargs)
objs.flatten!
map = multi_key_map(objs, context: context)
cache.fetch_multi(*map.keys, **kwargs) do |key|
yield map[key]
end
end
# @param objects [Enumerable<Object>] objects which _must_ respond to `#cache_key`
# @param context [Proc] a proc that can be called to help generate each cache key
# @return [Hash]
def multi_key_map(objects, context:)
objects.index_by do |object|
contextual_cache_key(object, context)
end
end
end
end
end
|
