1 files changed, 57 insertions, 6 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index e8a43e7bce..b7918c7f07 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -247,6 +247,10 @@ module ActiveRecord
         true
       end
 
+      def supports_index_sort_order?
+        true
+      end
+
       class StatementPool < ConnectionAdapters::StatementPool
         def initialize(connection, max)
           super
@@ -513,6 +517,48 @@ module ActiveRecord
 
       # DATABASE STATEMENTS ======================================
 
+      def explain(arel)
+        sql = "EXPLAIN #{to_sql(arel)}"
+        ExplainPrettyPrinter.new.pp(exec_query(sql))
+      end
+
+      class ExplainPrettyPrinter # :nodoc:
+        # Pretty prints the result of a EXPLAIN in a way that resembles the output of the
+        # PostgreSQL shell:
+        #
+        #                                     QUERY PLAN
+        #   ------------------------------------------------------------------------------
+        #    Nested Loop Left Join  (cost=0.00..37.24 rows=8 width=0)
+        #      Join Filter: (posts.user_id = users.id)
+        #      ->  Index Scan using users_pkey on users  (cost=0.00..8.27 rows=1 width=4)
+        #            Index Cond: (id = 1)
+        #      ->  Seq Scan on posts  (cost=0.00..28.88 rows=8 width=4)
+        #            Filter: (posts.user_id = 1)
+        #   (6 rows)
+        #
+        def pp(result)
+          header = result.columns.first
+          lines  = result.rows.map(&:first)
+
+          # We add 2 because there's one char of padding at both sides, note
+          # the extra hyphens in the example above.
+          width = [header, *lines].map(&:length).max + 2
+
+          pp = []
+
+          pp << header.center(width).rstrip
+          pp << '-' * width
+
+          pp += lines.map {|line| " #{line}"}
+
+          nrows = result.rows.length
+          rows_label = nrows == 1 ? 'row' : 'rows'
+          pp << "(#{nrows} #{rows_label})"
+
+          pp.join("\n") + "\n"
+        end
+      end
+
       # Executes a SELECT query and returns an array of rows. Each row is an
       # array of field values.
       def select_rows(sql, name = nil)
@@ -754,16 +800,15 @@ module ActiveRecord
 
       # Returns an array of indexes for the given table.
       def indexes(table_name, name = nil)
-         schemas = schema_search_path.split(/,/).map { |p| quote(p) }.join(',')
          result = query(<<-SQL, name)
-           SELECT distinct i.relname, d.indisunique, d.indkey, t.oid
+           SELECT distinct i.relname, d.indisunique, d.indkey, pg_get_indexdef(d.indexrelid), t.oid
            FROM pg_class t
            INNER JOIN pg_index d ON t.oid = d.indrelid
            INNER JOIN pg_class i ON d.indexrelid = i.oid
            WHERE i.relkind = 'i'
              AND d.indisprimary = 'f'
              AND t.relname = '#{table_name}'
-             AND i.relnamespace IN (SELECT oid FROM pg_namespace WHERE nspname IN (#{schemas}) )
+             AND i.relnamespace IN (SELECT oid FROM pg_namespace WHERE nspname = ANY (current_schemas(false)) )
           ORDER BY i.relname
         SQL
 
@@ -772,7 +817,8 @@ module ActiveRecord
           index_name = row[0]
           unique = row[1] == 't'
           indkey = row[2].split(" ")
-          oid = row[3]
+          inddef = row[3]
+          oid = row[4]
 
           columns = Hash[query(<<-SQL, "Columns for index #{row[0]} on #{table_name}")]
           SELECT a.attnum, a.attname
@@ -782,7 +828,12 @@ module ActiveRecord
           SQL
 
           column_names = columns.values_at(*indkey).compact
-          column_names.empty? ? nil : IndexDefinition.new(table_name, index_name, unique, column_names)
+
+          # add info on sort order for columns (only desc order is explicitly specified, asc is the default)
+          desc_order_columns = inddef.scan(/(\w+) DESC/).flatten
+          orders = desc_order_columns.any? ? Hash[desc_order_columns.map {|order_column| [order_column, :desc]}] : {}
+      
+          column_names.empty? ? nil : IndexDefinition.new(table_name, index_name, unique, column_names, [], orders)
         end.compact
       end
 
@@ -826,7 +877,7 @@ module ActiveRecord
 
       # Returns the active schema search path.
       def schema_search_path
-        @schema_search_path ||= query('SHOW search_path')[0][0]
+        @schema_search_path ||= query('SHOW search_path', 'SCHEMA')[0][0]
       end
 
       # Returns the current client message level.