Session variables for mysql, mysql2, and postgresql adapters can be set

in the new 'variables:' hash in each database config section in database.yml.
The key-value pairs of this hash will be sent in a 'SET key = value, ...'
query on new database connections.

The configure_connection methods from mysql and mysql2 into are
consolidated into the abstract_mysql base class.

Author: sodabrew

activerecord/CHANGELOG.md

@@ -1,5 +1,13 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*   Session variables can be set for the `mysql`, `mysql2`, and `postgresql` adapters
+    in the `variables: <hash>` parameter in `database.yml`. The key-value pairs of this
+    hash will be sent in a `SET key = value` query on new database connections. See also:
+    http://dev.mysql.com/doc/refman/5.0/en/set-statement.html
+    http://www.postgresql.org/docs/8.3/static/sql-set.html
+
+    *Aaron Stone*
+
 *   Allow `Relation#where` with no arguments to be chained with new `not` query method.
 
     Example:

activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb

@@ -704,6 +704,45 @@ def column_for(table_name, column_name)
         end
         column
       end
+
+      def configure_connection
+        variables = @config[:variables] || {}
+
+        # By default, MySQL 'where id is null' selects the last inserted id.
+        # Turn this off. http://dev.rubyonrails.org/ticket/6778
+        variables[:sql_auto_is_null] = 0
+
+        # Increase timeout so the server doesn't disconnect us.
+        wait_timeout = @config[:wait_timeout]
+        wait_timeout = 2147483 unless wait_timeout.is_a?(Fixnum)
+        variables[:wait_timeout] = wait_timeout
+
+        # Make MySQL reject illegal values rather than truncating or blanking them, see
+        # http://dev.mysql.com/doc/refman/5.0/en/server-sql-mode.html#sqlmode_strict_all_tables
+        # If the user has provided another value for sql_mode, don't replace it.
+        if strict_mode? && !variables.has_key?(:sql_mode)
+          variables[:sql_mode] = 'STRICT_ALL_TABLES'
+        end
+
+        # NAMES does not have an equals sign, see
+        # http://dev.mysql.com/doc/refman/5.0/en/set-statement.html#id944430
+        # (trailing comma because variable_assignments will always have content)
+        encoding = "NAMES #{@config[:encoding]}, " if @config[:encoding]
+
+        # Gather up all of the SET variables...
+        variable_assignments = variables.map do |k, v|
+          if v == ':default' || v == :default
+            "@@SESSION.#{k.to_s} = DEFAULT" # Sets the value to the global or compile default
+          elsif !v.nil?
+            "@@SESSION.#{k.to_s} = #{quote(v)}"
+          end
+          # or else nil; compact to clear nils out
+        end.compact.join(', ')
+
+        # ...and send them all in one query
+        execute("SET #{encoding} #{variable_assignments}", :skip_logging)
+      end
+
     end
   end
 end

activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb

@@ -251,27 +251,7 @@ def connect
 
       def configure_connection
         @connection.query_options.merge!(:as => :array)
-
-        # By default, MySQL 'where id is null' selects the last inserted id.
-        # Turn this off. http://dev.rubyonrails.org/ticket/6778
-        variable_assignments = ['SQL_AUTO_IS_NULL=0']
-
-        # Make MySQL reject illegal values rather than truncating or
-        # blanking them. See
-        # http://dev.mysql.com/doc/refman/5.5/en/server-sql-mode.html#sqlmode_strict_all_tables
-        variable_assignments << "SQL_MODE='STRICT_ALL_TABLES'" if strict_mode?
-
-        encoding = @config[:encoding]
-
-        # make sure we set the encoding
-        variable_assignments << "NAMES '#{encoding}'" if encoding
-
-        # increase timeout so mysql server doesn't disconnect us
-        wait_timeout = @config[:wait_timeout]
-        wait_timeout = 2147483 unless wait_timeout.is_a?(Fixnum)
-        variable_assignments << "@@wait_timeout = #{wait_timeout}"
-
-        execute("SET #{variable_assignments.join(', ')}", :skip_logging)
+        super
       end
 
       def version

activerecord/lib/active_record/connection_adapters/mysql_adapter.rb

@@ -51,7 +51,8 @@ module ConnectionAdapters
     # * <tt>:database</tt> - The name of the database. No default, must be provided.
     # * <tt>:encoding</tt> - (Optional) Sets the client encoding by executing "SET NAMES <encoding>" after connection.
     # * <tt>:reconnect</tt> - Defaults to false (See MySQL documentation: http://dev.mysql.com/doc/refman/5.0/en/auto-reconnect.html).
-    # * <tt>:strict</tt> - Defaults to true. Enable STRICT_ALL_TABLES. (See MySQL documentation: http://dev.mysql.com/doc/refman/5.5/en/server-sql-mode.html)
+    # * <tt>:strict</tt> - Defaults to true. Enable STRICT_ALL_TABLES. (See MySQL documentation: http://dev.mysql.com/doc/refman/5.0/en/server-sql-mode.html)
+    # * <tt>:variables</tt> - (Optional) A hash session variables to send as `SET @@SESSION.key = value` on each database connection. Use the value `:default` to set a variable to its DEFAULT value. (See MySQL documentation: http://dev.mysql.com/doc/refman/5.0/en/set-statement.html).
     # * <tt>:sslca</tt> - Necessary to use MySQL with an SSL connection.
     # * <tt>:sslkey</tt> - Necessary to use MySQL with an SSL connection.
     # * <tt>:sslcert</tt> - Necessary to use MySQL with an SSL connection.
@@ -535,18 +536,10 @@ def connect
         configure_connection
       end
 
+      # Many Rails applications monkey-patch a replacement of the configure_connection method
+      # and don't call 'super', so leave this here even though it looks superfluous.
       def configure_connection
-        encoding = @config[:encoding]
-        execute("SET NAMES '#{encoding}'", :skip_logging) if encoding
-
-        # By default, MySQL 'where id is null' selects the last inserted id.
-        # Turn this off. http://dev.rubyonrails.org/ticket/6778
-        execute("SET SQL_AUTO_IS_NULL=0", :skip_logging)
-
-        # Make MySQL reject illegal values rather than truncating or
-        # blanking them. See
-        # http://dev.mysql.com/doc/refman/5.5/en/server-sql-mode.html#sqlmode_strict_all_tables
-        execute("SET SQL_MODE='STRICT_ALL_TABLES'", :skip_logging) if strict_mode?
+        super
       end
 
       def select(sql, name = nil, binds = [])

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -24,7 +24,7 @@ def postgresql_connection(config) # :nodoc:
       # Forward any unused config params to PGconn.connect.
       [:statement_limit, :encoding, :min_messages, :schema_search_path,
        :schema_order, :adapter, :pool, :checkout_timeout, :template,
-       :reaping_frequency, :insert_returning].each do |key|
+       :reaping_frequency, :insert_returning, :variables].each do |key|
         conn_params.delete key
       end
       conn_params.delete_if { |k,v| v.nil? }
@@ -238,6 +238,8 @@ def simplified_type(field_type)
     #   <encoding></tt> call on the connection.
     # * <tt>:min_messages</tt> - An optional client min messages that is used in a
     #   <tt>SET client_min_messages TO <min_messages></tt> call on the connection.
+    # * <tt>:variables</tt> - An optional hash of additional parameters that
+    #   will be used in <tt>SET SESSION key = val</tt> calls on the connection.
     # * <tt>:insert_returning</tt> - An optional boolean to control the use or <tt>RETURNING</tt> for <tt>INSERT</tt> statements
     #   defaults to true.
     #
@@ -706,11 +708,24 @@ def configure_connection
 
           # If using Active Record's time zone support configure the connection to return
           # TIMESTAMP WITH ZONE types in UTC.
+          # (SET TIME ZONE does not use an equals sign like other SET variables)
           if ActiveRecord::Base.default_timezone == :utc
             execute("SET time zone 'UTC'", 'SCHEMA')
           elsif @local_tz
             execute("SET time zone '#{@local_tz}'", 'SCHEMA')
           end
+
+          # SET statements from :variables config hash
+          # http://www.postgresql.org/docs/8.3/static/sql-set.html
+          variables = @config[:variables] || {}
+          variables.map do |k, v|
+            if v == ':default' || v == :default
+              # Sets the value to the global or compile default
+              execute("SET SESSION #{k.to_s} TO DEFAULT", 'SCHEMA')
+            elsif !v.nil?
+              execute("SET SESSION #{k.to_s} TO #{quote(v)}", 'SCHEMA')
+            end
+          end
         end
 
         # Returns the current ID of a table's sequence.

activerecord/test/cases/adapters/mysql/connection_test.rb

@@ -137,6 +137,23 @@ def test_mysql_strict_mode_disabled_dont_override_global_sql_mode
     end
   end
 
+  def test_mysql_set_session_variable
+    run_without_connection do |orig_connection|
+      ActiveRecord::Base.establish_connection(orig_connection.deep_merge({:variables => {:default_week_format => 3}}))
+      session_mode = ActiveRecord::Base.connection.exec_query "SELECT @@SESSION.DEFAULT_WEEK_FORMAT"
+      assert_equal 3, session_mode.rows.first.first.to_i
+    end
+  end
+
+  def test_mysql_set_session_variable_to_default
+    run_without_connection do |orig_connection|
+      ActiveRecord::Base.establish_connection(orig_connection.deep_merge({:variables => {:default_week_format => :default}}))
+      global_mode = ActiveRecord::Base.connection.exec_query "SELECT @@GLOBAL.DEFAULT_WEEK_FORMAT"
+      session_mode = ActiveRecord::Base.connection.exec_query "SELECT @@SESSION.DEFAULT_WEEK_FORMAT"
+      assert_equal global_mode.rows, session_mode.rows
+    end
+  end
+
   private
 
   def run_without_connection

activerecord/test/cases/adapters/mysql2/connection_test.rb

@@ -53,6 +53,23 @@ def test_mysql_strict_mode_disabled_dont_override_global_sql_mode
     end
   end
 
+  def test_mysql_set_session_variable
+    run_without_connection do |orig_connection|
+      ActiveRecord::Base.establish_connection(orig_connection.deep_merge({:variables => {:default_week_format => 3}}))
+      session_mode = ActiveRecord::Base.connection.exec_query "SELECT @@SESSION.DEFAULT_WEEK_FORMAT"
+      assert_equal 3, session_mode.rows.first.first.to_i
+    end
+  end
+
+  def test_mysql_set_session_variable_to_default
+    run_without_connection do |orig_connection|
+      ActiveRecord::Base.establish_connection(orig_connection.deep_merge({:variables => {:default_week_format => :default}}))
+      global_mode = ActiveRecord::Base.connection.exec_query "SELECT @@GLOBAL.DEFAULT_WEEK_FORMAT"
+      session_mode = ActiveRecord::Base.connection.exec_query "SELECT @@SESSION.DEFAULT_WEEK_FORMAT"
+      assert_equal global_mode.rows, session_mode.rows
+    end
+  end
+
   def test_logs_name_structure_dump
     @connection.structure_dump
     assert_equal "SCHEMA", @connection.logged[0][1]

activerecord/test/cases/adapters/postgresql/connection_test.rb

@@ -154,5 +154,46 @@ def test_reconnection_after_actual_disconnection_with_verify
       end
     end
 
+    def test_set_session_variable_true
+      run_without_connection do |orig_connection|
+        ActiveRecord::Base.establish_connection(orig_connection.deep_merge({:variables => {:debug_print_plan => true}}))
+        set_true = ActiveRecord::Base.connection.exec_query "SHOW DEBUG_PRINT_PLAN"
+        assert_equal set_true.rows, [["on"]]
+      end
+    end
+
+    def test_set_session_variable_false
+      run_without_connection do |orig_connection|
+        ActiveRecord::Base.establish_connection(orig_connection.deep_merge({:variables => {:debug_print_plan => false}}))
+        set_false = ActiveRecord::Base.connection.exec_query "SHOW DEBUG_PRINT_PLAN"
+        assert_equal set_false.rows, [["off"]]
+      end
+    end
+
+    def test_set_session_variable_nil
+      run_without_connection do |orig_connection|
+        # This should be a no-op that does not raise an error
+        ActiveRecord::Base.establish_connection(orig_connection.deep_merge({:variables => {:debug_print_plan => nil}}))
+      end
+    end
+
+    def test_set_session_variable_default
+      run_without_connection do |orig_connection|
+        # This should execute a query that does not raise an error
+        ActiveRecord::Base.establish_connection(orig_connection.deep_merge({:variables => {:debug_print_plan => :default}}))
+      end
+    end
+
+    private
+
+    def run_without_connection
+      original_connection = ActiveRecord::Base.remove_connection
+      begin
+        yield original_connection
+      ensure
+        ActiveRecord::Base.establish_connection(original_connection)
+      end
+    end
+
   end
 end