4 files changed, 14 insertions, 3 deletions
diff --git a/activerecord/lib/active_record/explain.rb b/activerecord/lib/active_record/explain.rb
index e65dab07ba..727a9befc1 100644
--- a/activerecord/lib/active_record/explain.rb
+++ b/activerecord/lib/active_record/explain.rb
@@ -27,7 +27,7 @@ module ActiveRecord
         end.join("\n")
       end.join("\n")
 
-      # Overriding inspect to be more human readable, specially in the console.
+      # Overriding inspect to be more human readable, especially in the console.
       def str.inspect
         self
       end
diff --git a/activerecord/lib/active_record/migration/join_table.rb b/activerecord/lib/active_record/migration/join_table.rb
index ebf64cbcdc..05569fadbd 100644
--- a/activerecord/lib/active_record/migration/join_table.rb
+++ b/activerecord/lib/active_record/migration/join_table.rb
@@ -8,7 +8,7 @@ module ActiveRecord
       end
 
       def join_table_name(table_1, table_2)
-        [table_1.to_s, table_2.to_s].sort.join("_").to_sym
+        ModelSchema.derive_join_table_name(table_1, table_2).to_sym
       end
     end
   end
diff --git a/activerecord/lib/active_record/model_schema.rb b/activerecord/lib/active_record/model_schema.rb
index 092c3b4fb7..850220babd 100644
--- a/activerecord/lib/active_record/model_schema.rb
+++ b/activerecord/lib/active_record/model_schema.rb
@@ -55,6 +55,17 @@ module ActiveRecord
       delegate :type_for_attribute, to: :class
     end
 
+    # Derives the join table name for +first_table+ and +second_table+. The
+    # table names appear in alphabetical order. A common prefix is removed
+    # (useful for namespaced models like Music::Artist and Music::Record):
+    #
+    #   artists, records => artists_records
+    #   records, artists => artists_records
+    #   music_artists, music_records => music_artists_records
+    def self.derive_join_table_name(first_table, second_table) # :nodoc:
+      [first_table.to_s, second_table.to_s].sort.join("\0").gsub(/^(.*_)(.+)\0\1(.+)/, '\1\2_\3').gsub("\0", "_")
+    end
+
     module ClassMethods
       # Guesses the table name (in forced lower-case) based on the name of the class in the
       # inheritance hierarchy descending directly from ActiveRecord::Base. So if the hierarchy
diff --git a/activerecord/lib/active_record/reflection.rb b/activerecord/lib/active_record/reflection.rb
index 2eefba2dfe..86eef9ca36 100644
--- a/activerecord/lib/active_record/reflection.rb
+++ b/activerecord/lib/active_record/reflection.rb
@@ -567,7 +567,7 @@ Joining, Preloading and eager loading of these associations is deprecated and wi
         end
 
         def derive_join_table
-          [active_record.table_name, klass.table_name].sort.join("\0").gsub(/^(.*_)(.+)\0\1(.+)/, '\1\2_\3').gsub("\0", "_")
+          ModelSchema.derive_join_table_name active_record.table_name, klass.table_name
         end
 
         def primary_key(klass)