rdoc for some of the methods in JoinDependency

activerecord/lib/active_record/associations/join_dependency.rb

@@ -7,6 +7,27 @@ class JoinDependency # :nodoc:
 
       attr_reader :join_parts, :reflections, :alias_tracker, :base_klass
 
+      # base is the base class on which operation is taking place.
+      # associations is the list of associations which are joined using hash, symbol or array.
+      # joins is the list of all string join commnads and arel nodes.
+      #
+      #  Example :
+      #
+      #  class Physician < ActiveRecord::Base
+      #    has_many :appointments
+      #    has_many :patients, through: :appointments
+      #  end
+      #
+      #  If I execute `@physician.patients.to_a` then
+      #    base #=> Physician
+      #    associations #=> []
+      #    joins #=>  [#<Arel::Nodes::InnerJoin: ...]
+      #
+      #  However if I execute `Physician.joins(:appointments).to_a` then
+      #    base #=> Physician
+      #    associations #=> [:appointments]
+      #    joins #=>  []
+      #
       def initialize(base, associations, joins)
         @base_klass    = base
         @table_joins   = joins

activerecord/lib/active_record/associations/join_dependency/join_association.rb

@@ -123,6 +123,21 @@ def join_to(manager)
           manager
         end
 
+        #  Builds equality condition.
+        #
+        #  Example:
+        #
+        #  class Physician < ActiveRecord::Base
+        #    has_many :appointments
+        #  end
+        #
+        #  If I execute `Physician.joins(:appointments).to_a` then
+        #    reflection    #=> #<ActiveRecord::Reflection::AssociationReflection @macro=:has_many ...>
+        #    table         #=> #<Arel::Table @name="appointments" ...>
+        #    key           #=>  physician_id
+        #    foreign_table #=> #<Arel::Table @name="physicians" ...>
+        #    foreign_key   #=> id
+        #
         def build_constraint(reflection, table, key, foreign_table, foreign_key)
           constraint = table[key].eq(foreign_table[foreign_key])