144 lines
4.2 KiB
Ruby
144 lines
4.2 KiB
Ruby
# Copyright (C) 2012 Instructure, Inc.
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#
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# This file is part of Canvas.
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#
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# Canvas is free software: you can redistribute it and/or modify it under
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# the terms of the GNU Affero General Public License as published by the Free
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# Software Foundation, version 3 of the License.
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#
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# Canvas is distributed in the hope that it will be useful, but WITHOUT ANY
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# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
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# A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
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# details.
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#
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# You should have received a copy of the GNU Affero General Public License along
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# with this program. If not, see <http://www.gnu.org/licenses/>.
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#
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# on-demand in-memory model caching for those times where the rails query
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# cache can't help you, like in this contrived example:
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#
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# # given:
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#
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# class Foo < ActiveRecord::Base
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# has_many :bars
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# end
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#
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# class Bar < ActiveRecord::Base
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# belongs_to :foo
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# def something!
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# update_attribute :stuff, "my foo is: #{foo.name}"
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# end
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# end
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#
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# # if you do:
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# foo.bars.each(&:something!)
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#
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# # then by default, AR loads each bar's foo separately and won't use the
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# # query cache, since each update blows it away.
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#
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# granted, the example is a bit contrived, as preloading would be one possible
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# solution. ModelCache is useful for those times when preloading is just not
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# feasible. See Conversation and ConversatonParticipant for real-world usage.
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module ModelCache
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module ClassMethods
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# e.g. use this to cache calls to ConversationParticipant#conversation,
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# no matter how those conversation_participants were loaded
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def cacheable_method(method, options={})
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options[:cache_name] ||= method.to_s.pluralize.to_sym
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options[:key_method] ||= "#{method}_id"
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options[:key_lookup] ||= :id
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options[:type] ||= :instance
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ModelCache.make_cacheable self, method, options
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end
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# e.g. use this to cache calls to Conversation.find_by_id
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def cacheable_by(*keys)
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keys.each do |key|
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ModelCache.keys[self.name] << key
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ModelCache.make_cacheable self, "find_by_#{key}", :key_lookup => key
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end
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end
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end
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module InstanceMethods
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def add_to_caches
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return unless cache = ModelCache[self.class.name.underscore.pluralize.to_sym]
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cache.keys.each do |key|
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cache[key][send(key)] = self
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end
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end
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def update_in_caches
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return unless cache = ModelCache[self.class.name.underscore.pluralize.to_sym]
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cache.keys.each do |key|
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if send("#{key}_changed?")
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cache[key][send(key)] = self
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cache[key].delete(send("#{key}_was"))
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end
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end
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end
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end
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def self.with_cache(lookups)
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@cache = lookups.inject({}){ |h, (k, v)| h[k] = prepare_lookups(v); h }
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yield
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ensure
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@cache = nil
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end
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def self.[](cache_name)
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return nil unless @cache
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@cache[cache_name] || {}
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end
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def self.keys
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@keys ||= Hash.new{ |h, k| h[k] = [] }
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end
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def self.prepare_lookups(records)
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return records if records.is_a?(Hash)
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return {} if records.empty?
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keys[records.first.class.name].inject({}) do |h, k|
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h[k] = records.index_by(&k)
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h
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end
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end
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def self.make_cacheable(klass, method, options={})
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options[:type] ||= :class
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options[:cache_name] ||= klass.name.underscore.pluralize.to_sym
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options[:key_lookup] ||= method
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orig_method = "super"
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alias_method = nil
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key_value = options[:key_method] || "args.first"
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# if extra args are provided, we should clear out the current value
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# (e.g. if you call c.user(:lock => true) )
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expected_args = options[:key_method] ? 0 : 1
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maybe_reset = "cache[#{key_value}] = #{orig_method} if args.size > #{expected_args}"
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klass.send(options[:type] == :instance ? :class_eval : :instance_eval, <<-CODE, __FILE__, __LINE__+1)
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def #{method}(*args)
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if cache = ModelCache[#{options[:cache_name].inspect}] and cache = cache[#{options[:key_lookup].inspect}]
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#{maybe_reset}
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cache[#{key_value}]
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else
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#{orig_method}
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end
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end
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#{alias_method}
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CODE
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end
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def self.included(klass)
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klass.send :include, InstanceMethods
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klass.extend ClassMethods
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klass.after_create :add_to_caches
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klass.after_update :update_in_caches
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end
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end
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