Merge pull request #20025 from kamipo/dont_use_exec_query_for_performance

Use `select_value` for avoid `ActiveRecord::Result` instance creating

2 files changed, 17 insertions, 22 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
index 662c6b4d38..686671b007 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
@@ -70,7 +70,7 @@ module ActiveRecord
 
         # Returns the list of all tables in the schema search path or a specified schema.
         def tables(name = nil)
-          query(<<-SQL, 'SCHEMA').map { |row| row[0] }
+          select_values(<<-SQL, 'SCHEMA')
             SELECT tablename
             FROM pg_tables
             WHERE schemaname = ANY (current_schemas(false))
@@ -84,7 +84,7 @@ module ActiveRecord
           name = Utils.extract_schema_qualified_name(name.to_s)
           return false unless name.identifier
 
-          exec_query(<<-SQL, 'SCHEMA').rows.first[0].to_i > 0
+          select_value(<<-SQL, 'SCHEMA').to_i > 0
               SELECT COUNT(*)
               FROM pg_class c
               LEFT JOIN pg_namespace n ON n.oid = c.relnamespace
@@ -100,7 +100,7 @@ module ActiveRecord
 
         # Returns true if schema exists.
         def schema_exists?(name)
-          exec_query(<<-SQL, 'SCHEMA').rows.first[0].to_i > 0
+          select_value(<<-SQL, 'SCHEMA').to_i > 0
             SELECT COUNT(*)
             FROM pg_namespace
             WHERE nspname = '#{name}'
@@ -109,7 +109,7 @@ module ActiveRecord
 
         # Verifies existence of an index with a given name.
         def index_name_exists?(table_name, index_name, default)
-          exec_query(<<-SQL, 'SCHEMA').rows.first[0].to_i > 0
+          select_value(<<-SQL, 'SCHEMA').to_i > 0
             SELECT COUNT(*)
             FROM pg_class t
             INNER JOIN pg_index d ON t.oid = d.indrelid
@@ -182,17 +182,17 @@ module ActiveRecord
 
         # Returns the current database name.
         def current_database
-          query('select current_database()', 'SCHEMA')[0][0]
+          select_value('select current_database()', 'SCHEMA')
         end
 
         # Returns the current schema name.
         def current_schema
-          query('SELECT current_schema', 'SCHEMA')[0][0]
+          select_value('SELECT current_schema', 'SCHEMA')
         end
 
         # Returns the current database encoding format.
         def encoding
-          query(<<-end_sql, 'SCHEMA')[0][0]
+          select_value(<<-end_sql, 'SCHEMA')
             SELECT pg_encoding_to_char(pg_database.encoding) FROM pg_database
             WHERE pg_database.datname LIKE '#{current_database}'
           end_sql
@@ -200,21 +200,21 @@ module ActiveRecord
 
         # Returns the current database collation.
         def collation
-          query(<<-end_sql, 'SCHEMA')[0][0]
+          select_value(<<-end_sql, 'SCHEMA')
             SELECT pg_database.datcollate FROM pg_database WHERE pg_database.datname LIKE '#{current_database}'
           end_sql
         end
 
         # Returns the current database ctype.
         def ctype
-          query(<<-end_sql, 'SCHEMA')[0][0]
+          select_value(<<-end_sql, 'SCHEMA')
             SELECT pg_database.datctype FROM pg_database WHERE pg_database.datname LIKE '#{current_database}'
           end_sql
         end
 
         # Returns an array of schema names.
         def schema_names
-          query(<<-SQL, 'SCHEMA').flatten
+          select_values(<<-SQL, 'SCHEMA')
             SELECT nspname
               FROM pg_namespace
              WHERE nspname !~ '^pg_.*'
@@ -247,12 +247,12 @@ module ActiveRecord
 
         # Returns the active schema search path.
         def schema_search_path
-          @schema_search_path ||= query('SHOW search_path', 'SCHEMA')[0][0]
+          @schema_search_path ||= select_value('SHOW search_path', 'SCHEMA')
         end
 
         # Returns the current client message level.
         def client_min_messages
-          query('SHOW client_min_messages', 'SCHEMA')[0][0]
+          select_value('SHOW client_min_messages', 'SCHEMA')
         end
 
         # Set the client message level.
@@ -270,10 +270,7 @@ module ActiveRecord
         end
 
         def serial_sequence(table, column)
-          result = exec_query(<<-eosql, 'SCHEMA')
-            SELECT pg_get_serial_sequence('#{table}', '#{column}')
-          eosql
-          result.rows.first.first
+          select_value("SELECT pg_get_serial_sequence('#{table}', '#{column}')", 'SCHEMA')
         end
 
         # Sets the sequence of a table's primary key to the specified value.
@@ -284,9 +281,7 @@ module ActiveRecord
             if sequence
               quoted_sequence = quote_table_name(sequence)
 
-              select_value <<-end_sql, 'SCHEMA'
-              SELECT setval('#{quoted_sequence}', #{value})
-              end_sql
+              select_value("SELECT setval('#{quoted_sequence}', #{value})", 'SCHEMA')
             else
               @logger.warn "#{table} has primary key #{pk} with no default sequence" if @logger
             end
@@ -309,7 +304,7 @@ module ActiveRecord
           if pk && sequence
             quoted_sequence = quote_table_name(sequence)
 
-            select_value <<-end_sql, 'SCHEMA'
+            select_value(<<-end_sql, 'SCHEMA')
               SELECT setval('#{quoted_sequence}', (SELECT COALESCE(MAX(#{quote_column_name pk})+(SELECT increment_by FROM #{quoted_sequence}), (SELECT min_value FROM #{quoted_sequence})) FROM #{quote_table_name(table)}), false)
             end_sql
           end
@@ -371,7 +366,7 @@ module ActiveRecord
 
         # Returns just a table's primary key
         def primary_key(table)
-          pks = exec_query(<<-end_sql, 'SCHEMA').rows
+          pks = query(<<-end_sql, 'SCHEMA')
             SELECT attr.attname
             FROM pg_attribute attr
             INNER JOIN pg_constraint cons ON attr.attrelid = cons.conrelid AND attr.attnum = any(cons.conkey)
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 7e15c2ab26..2b33a5b9cb 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -770,7 +770,7 @@ module ActiveRecord
         #  - format_type includes the column size constraint, e.g. varchar(50)
         #  - ::regclass is a function that gives the id for a table name
         def column_definitions(table_name) # :nodoc:
-          exec_query(<<-end_sql, 'SCHEMA').rows
+          query(<<-end_sql, 'SCHEMA')
               SELECT a.attname, format_type(a.atttypid, a.atttypmod),
                      pg_get_expr(d.adbin, d.adrelid), a.attnotnull, a.atttypid, a.atttypmod,
              (SELECT c.collname FROM pg_collation c, pg_type t