1 files changed, 85 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/associations/alias_tracker.rb b/activerecord/lib/active_record/associations/alias_tracker.rb
new file mode 100644
index 0000000000..634dee2289
--- /dev/null
+++ b/activerecord/lib/active_record/associations/alias_tracker.rb
@@ -0,0 +1,85 @@
+require 'active_support/core_ext/string/conversions'
+
+module ActiveRecord
+  module Associations
+    # Keeps track of table aliases for ActiveRecord::Associations::ClassMethods::JoinDependency and
+    # ActiveRecord::Associations::ThroughAssociationScope
+    class AliasTracker # :nodoc:
+      attr_reader :aliases, :table_joins
+
+      # table_joins is an array of arel joins which might conflict with the aliases we assign here
+      def initialize(table_joins = [])
+        @aliases     = Hash.new
+        @table_joins = table_joins
+      end
+
+      def aliased_table_for(table_name, aliased_name = nil)
+        table_alias = aliased_name_for(table_name, aliased_name)
+
+        if table_alias == table_name
+          Arel::Table.new(table_name)
+        else
+          Arel::Table.new(table_name).alias(table_alias)
+        end
+      end
+
+      def aliased_name_for(table_name, aliased_name = nil)
+        aliased_name ||= table_name
+
+        initialize_count_for(table_name) if aliases[table_name].nil?
+
+        if aliases[table_name].zero?
+          # If it's zero, we can have our table_name
+          aliases[table_name] = 1
+          table_name
+        else
+          # Otherwise, we need to use an alias
+          aliased_name = connection.table_alias_for(aliased_name)
+
+          initialize_count_for(aliased_name) if aliases[aliased_name].nil?
+
+          # Update the count
+          aliases[aliased_name] += 1
+
+          if aliases[aliased_name] > 1
+            "#{truncate(aliased_name)}_#{aliases[aliased_name]}"
+          else
+            aliased_name
+          end
+        end
+      end
+
+      def pluralize(table_name)
+        ActiveRecord::Base.pluralize_table_names ? table_name.to_s.pluralize : table_name
+      end
+
+      private
+
+        def initialize_count_for(name)
+          aliases[name] = 0
+
+          unless Arel::Table === table_joins
+            # quoted_name should be downcased as some database adapters (Oracle) return quoted name in uppercase
+            quoted_name = connection.quote_table_name(name).downcase
+
+            aliases[name] += table_joins.map { |join|
+              # Table names + table aliases
+              join.left.downcase.scan(
+                /join(?:\s+\w+)?\s+(\S+\s+)?#{quoted_name}\son/
+              ).size
+            }.sum
+          end
+
+          aliases[name]
+        end
+
+        def truncate(name)
+          name[0..connection.table_alias_length-3]
+        end
+
+        def connection
+          ActiveRecord::Base.connection
+        end
+    end
+  end
+end