Merge pull request #8966 from cfabianski/disable_prepared_statement_when_preparing_a_query

Unprepared Visitor + unprepared_statement

Conflicts:
	activerecord/CHANGELOG.md

activerecord/CHANGELOG.md

 ## Rails 4.0.0 (unreleased) ##
 
+*   Created block to by-pass the prepared statement bindings.
+    This will allow to compose fragments of large SQL statements to
+    avoid multiple round-trips between Ruby and the DB.
+
+    Example:
+
+        sql = Post.connection.unprepared_statement do
+            Post.first.comments.to_sql
+        end
+
+    *Cédric Fabianski*
+
 *   Change the semantics of combining scopes to be the same as combining
     class methods which return scopes. For example:
 

activerecord/lib/active_record/connection_adapters/abstract_adapter.rb

@@ -118,6 +118,17 @@ def expire
         @in_use = false
       end
 
+      def unprepared_visitor
+        self.class::BindSubstitution.new self
+      end
+
+      def unprepared_statement
+        old, @visitor = @visitor, unprepared_visitor
+        yield
+      ensure
+        @visitor = old
+      end
+
       # Returns the human-readable name of the adapter. Use mixed case - one
       # can always use downcase if needed.
       def adapter_name

activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb

@@ -143,7 +143,7 @@ def initialize(connection, logger, connection_options, config)
         if self.class.type_cast_config_to_boolean(config.fetch(:prepared_statements) { true })
           @visitor = Arel::Visitors::MySQL.new self
         else
-          @visitor = BindSubstitution.new self
+          @visitor = unprepared_visitor
         end
       end
 

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -489,7 +489,7 @@ def initialize(connection, logger, connection_parameters, config)
         if self.class.type_cast_config_to_boolean(config.fetch(:prepared_statements) { true })
           @visitor = Arel::Visitors::PostgreSQL.new self
         else
-          @visitor = BindSubstitution.new self
+          @visitor = unprepared_visitor
         end
 
         @connection_parameters, @config = connection_parameters, config

activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb

@@ -113,7 +113,7 @@ def initialize(connection, logger, config)
         if self.class.type_cast_config_to_boolean(config.fetch(:prepared_statements) { true })
           @visitor = Arel::Visitors::SQLite.new self
         else
-          @visitor = BindSubstitution.new self
+          @visitor = unprepared_visitor
         end
       end
 

activerecord/test/cases/relations_test.rb

@@ -714,6 +714,13 @@ def test_relation_merging
     assert_equal [developers(:poor_jamis)], dev_with_count.to_a
   end
 
+  def test_relation_to_sql
+    sql = Post.connection.unprepared_statement do
+      Post.first.comments.to_sql
+    end
+    assert_no_match(/\?/, sql)
+  end
+
   def test_relation_merging_with_arel_equalities_keeps_last_equality
     devs = Developer.where(Developer.arel_table[:salary].eq(80000)).merge(
       Developer.where(Developer.arel_table[:salary].eq(9000))