Split out most of the AR::Base code into separate modules :cake:

1 files changed, 167 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/inheritance.rb b/activerecord/lib/active_record/inheritance.rb
new file mode 100644
index 0000000000..de9461982a
--- /dev/null
+++ b/activerecord/lib/active_record/inheritance.rb
@@ -0,0 +1,167 @@
+require 'active_support/concern'
+
+module ActiveRecord
+  module Inheritance
+    extend ActiveSupport::Concern
+
+    included do
+      # Determine whether to store the full constant name including namespace when using STI
+      class_attribute :store_full_sti_class
+      self.store_full_sti_class = true
+    end
+
+    module ClassMethods
+      # True if this isn't a concrete subclass needing a STI type condition.
+      def descends_from_active_record?
+        if superclass.abstract_class?
+          superclass.descends_from_active_record?
+        else
+          superclass == Base || !columns_hash.include?(inheritance_column)
+        end
+      end
+
+      def finder_needs_type_condition? #:nodoc:
+        # This is like this because benchmarking justifies the strange :false stuff
+        :true == (@finder_needs_type_condition ||= descends_from_active_record? ? :false : :true)
+      end
+
+      def symbolized_base_class
+        @symbolized_base_class ||= base_class.to_s.to_sym
+      end
+
+      def symbolized_sti_name
+        @symbolized_sti_name ||= sti_name.present? ? sti_name.to_sym : symbolized_base_class
+      end
+
+      # Returns the base AR subclass that this class descends from. If A
+      # extends AR::Base, A.base_class will return A. If B descends from A
+      # through some arbitrarily deep hierarchy, B.base_class will return A.
+      #
+      # If B < A and C < B and if A is an abstract_class then both B.base_class
+      # and C.base_class would return B as the answer since A is an abstract_class.
+      def base_class
+        class_of_active_record_descendant(self)
+      end
+
+      # Set this to true if this is an abstract class (see <tt>abstract_class?</tt>).
+      attr_accessor :abstract_class
+
+      # Returns whether this class is an abstract class or not.
+      def abstract_class?
+        defined?(@abstract_class) && @abstract_class == true
+      end
+
+      def sti_name
+        store_full_sti_class ? name : name.demodulize
+      end
+
+      # Finder methods must instantiate through this method to work with the
+      # single-table inheritance model that makes it possible to create
+      # objects of different types from the same table.
+      def instantiate(record)
+        sti_class = find_sti_class(record[inheritance_column])
+        record_id = sti_class.primary_key && record[sti_class.primary_key]
+
+        if ActiveRecord::IdentityMap.enabled? && record_id
+          if (column = sti_class.columns_hash[sti_class.primary_key]) && column.number?
+            record_id = record_id.to_i
+          end
+          if instance = IdentityMap.get(sti_class, record_id)
+            instance.reinit_with('attributes' => record)
+          else
+            instance = sti_class.allocate.init_with('attributes' => record)
+            IdentityMap.add(instance)
+          end
+        else
+          instance = sti_class.allocate.init_with('attributes' => record)
+        end
+
+        instance
+      end
+
+      protected
+
+      # Returns the class descending directly from ActiveRecord::Base or an
+      # abstract class, if any, in the inheritance hierarchy.
+      def class_of_active_record_descendant(klass)
+        if klass == Base || klass.superclass == Base || klass.superclass.abstract_class?
+          klass
+        elsif klass.superclass.nil?
+          raise ActiveRecordError, "#{name} doesn't belong in a hierarchy descending from ActiveRecord"
+        else
+          class_of_active_record_descendant(klass.superclass)
+        end
+      end
+
+      # Returns the class type of the record using the current module as a prefix. So descendants of
+      # MyApp::Business::Account would appear as MyApp::Business::AccountSubclass.
+      def compute_type(type_name)
+        if type_name.match(/^::/)
+          # If the type is prefixed with a scope operator then we assume that
+          # the type_name is an absolute reference.
+          ActiveSupport::Dependencies.constantize(type_name)
+        else
+          # Build a list of candidates to search for
+          candidates = []
+          name.scan(/::|$/) { candidates.unshift "#{$`}::#{type_name}" }
+          candidates << type_name
+
+          candidates.each do |candidate|
+            begin
+              constant = ActiveSupport::Dependencies.constantize(candidate)
+              return constant if candidate == constant.to_s
+            rescue NameError => e
+              # We don't want to swallow NoMethodError < NameError errors
+              raise e unless e.instance_of?(NameError)
+            end
+          end
+
+          raise NameError, "uninitialized constant #{candidates.first}"
+        end
+      end
+
+      private
+
+      def find_sti_class(type_name)
+        if type_name.blank? || !columns_hash.include?(inheritance_column)
+          self
+        else
+          begin
+            if store_full_sti_class
+              ActiveSupport::Dependencies.constantize(type_name)
+            else
+              compute_type(type_name)
+            end
+          rescue NameError
+            raise SubclassNotFound,
+              "The single-table inheritance mechanism failed to locate the subclass: '#{type_name}'. " +
+              "This error is raised because the column '#{inheritance_column}' is reserved for storing the class in case of inheritance. " +
+              "Please rename this column if you didn't intend it to be used for storing the inheritance class " +
+              "or overwrite #{name}.inheritance_column to use another column for that information."
+          end
+        end
+      end
+
+      def type_condition(table = arel_table)
+        sti_column = table[inheritance_column.to_sym]
+        sti_names  = ([self] + descendants).map { |model| model.sti_name }
+
+        sti_column.in(sti_names)
+      end
+    end
+
+    private
+
+    # Sets the attribute used for single table inheritance to this class name if this is not the
+    # ActiveRecord::Base descendant.
+    # Considering the hierarchy Reply < Message < ActiveRecord::Base, this makes it possible to
+    # do Reply.new without having to set <tt>Reply[Reply.inheritance_column] = "Reply"</tt> yourself.
+    # No such attribute would be set for objects of the Message class in that example.
+    def ensure_proper_type
+      klass = self.class
+      if klass.finder_needs_type_condition?
+        write_attribute(klass.inheritance_column, klass.sti_name)
+      end
+    end
+  end
+end