Add fetch_multi_by_* support for cache_index with a single field

README.md

@@ -78,6 +78,9 @@ end
 # If the object isn't in the cache it is pulled from the db and stored in the cache.
 product = Product.fetch_by_handle(handle)
 
+# Fetch multiple products by providing an array of index values.
+products = Product.fetch_multi_by_handle(handles)
+
 products = Product.fetch_by_vendor_and_product_type(vendor, product_type)
 ```
 

lib/identity_cache/configuration_dsl.rb

@@ -64,6 +64,16 @@ def fetch_by_#{field_list}(#{arg_list}, includes: nil)
             end
           CODE
         end
+
+        if fields.length == 1
+          self.instance_eval(ruby = <<-CODE, __FILE__, __LINE__ + 1)
+            def fetch_multi_by_#{field_list}(index_values, includes: nil)
+              ids = fetch_multi_id_by_#{field_list}(index_values).values.flatten(1)
+              return ids if ids.empty?
+              fetch_multi(ids, includes: includes)
+            end
+          CODE
+        end
       end
 
 
@@ -185,6 +195,14 @@ def fetch_#{alias_name}_by_#{field_list}(#{arg_list})
             attribute_dynamic_fetcher(#{attribute}, #{fields.inspect}, [#{arg_list}], #{unique})
           end
         CODE
+
+        if fields.length == 1
+          self.instance_eval(<<-CODE, __FILE__, __LINE__ + 1)
+            def fetch_multi_#{alias_name}_by_#{field_list}(index_values)
+              batch_attribute_dynamic_fetcher(#{attribute}, #{fields.first.to_s.inspect}.freeze, index_values, #{unique})
+            end
+          CODE
+        end
       end
 
       def build_recursive_association_cache(association, options) #:nodoc:
@@ -272,6 +290,52 @@ def dynamic_attribute_cache_miss(attribute, fields, values, unique_index)
         unique_index ? results.first : results
       end
 
+      def batch_attribute_dynamic_fetcher(attribute, field, index_values, unique_index)
+        raise_if_scoped
+
+        type = type_for_attribute(field)
+        index_values = index_values.map { |value| type.cast(value) }
+
+        unless should_use_cache?
+          return batch_dynamic_attribute_cache_miss(attribute, field, index_values, unique_index)
+        end
+
+        fields = [field]
+        index_by_cache_key = index_values.each_with_object({}) do |index_value, index_by_cache_key|
+          cache_key = rails_cache_key_for_attribute_and_fields_and_values(attribute, fields, [index_value], unique_index)
+          index_by_cache_key[cache_key] = index_value
+        end
+        attribute_by_cache_key = IdentityCache.fetch_multi(index_by_cache_key.keys) do |unresolved_keys|
+          unresolved_index_values = unresolved_keys.map { |cache_key| index_by_cache_key.fetch(cache_key) }
+          resolved_attributes = batch_dynamic_attribute_cache_miss(attribute, field, unresolved_index_values, unique_index)
+          unresolved_index_values.map { |index_value| resolved_attributes.fetch(index_value) }
+        end
+        result = {}
+        attribute_by_cache_key.each do |cache_key, attribute_value|
+          result[index_by_cache_key.fetch(cache_key)] = attribute_value
+        end
+        result
+      end
+
+      def batch_dynamic_attribute_cache_miss(attribute, index_field, values, unique_index)
+        rows = reorder(nil).where(index_field => values).pluck(index_field, attribute)
+        result = {}
+        default = unique_index ? nil : []
+        values.each do |index_value|
+          result[index_value] = default.dup
+        end
+        if unique_index
+          rows.each do |index_value, attribute_value|
+            result[index_value] = attribute_value
+          end
+        else
+          rows.each do |index_value, attribute_value|
+            result[index_value] << attribute_value
+          end
+        end
+        result
+      end
+
       def ensure_base_model
         if self != cached_model
           raise DerivedModelError, "IdentityCache class methods must be called on the same model that includes IdentityCache"

test/fetch_multi_by_test.rb

@@ -0,0 +1,61 @@
+require "test_helper"
+
+class FetchMultiByTest < IdentityCache::TestCase
+  NAMESPACE = IdentityCache::CacheKeyGeneration::DEFAULT_NAMESPACE
+
+  def setup
+    super
+    @bob = Item.new
+    @bob.id = 1
+    @bob.title = 'bob'
+
+    @bertha = Item.new
+    @bertha.id = 2
+    @bertha.title = 'bertha'
+  end
+
+  def test_fetch_multi_by_cache_key
+    Item.cache_index :title, unique: false
+
+    @bob.save!
+    @bertha.save!
+
+    assert_equal [@bob], Item.fetch_by_title('bob')
+
+    assert_equal [@bob, @bertha], Item.fetch_multi_by_title(['bob', 'bertha'])
+  end
+
+  def test_fetch_multi_by_unique_cache_key
+    Item.cache_index :title, unique: true
+
+    @bob.save!
+    @bertha.save!
+
+    assert_equal @bob, Item.fetch_by_title('bob')
+
+    assert_equal [@bob, @bertha], Item.fetch_multi_by_title(['bob', 'bertha'])
+  end
+
+  def test_fetch_multi_attribute_by_cache_key
+    Item.cache_attribute :title, by: :id, unique: false
+
+    @bob.save!
+    @bertha.save!
+
+    assert_equal ['bob'], Item.fetch_title_by_id(1)
+
+    assert_equal({ 1 => ['bob'], 2 => ['bertha'] }, Item.fetch_multi_title_by_id([1, 2]))
+  end
+
+
+  def test_fetch_multi_attribute_by_unique_cache_key
+    Item.cache_attribute :title, by: :id, unique: true
+
+    @bob.save!
+    @bertha.save!
+
+    assert_equal 'bob', Item.fetch_title_by_id(1)
+
+    assert_equal({ 1 => 'bob', 2 => 'bertha' }, Item.fetch_multi_title_by_id([1, 2]))
+  end
+end

test/index_cache_test.rb

@@ -14,7 +14,7 @@ def test_fetch_with_garbage_input
     Item.cache_index :title, :id
 
     assert_queries(1) do
-      assert_equal [], Item.fetch_by_title_and_id('garbage', 'garbage')
+      assert_equal [], Item.fetch_by_title_and_id('garbage_title', 'garbage_id')
     end
   end