change query strategy based on adapter

activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb

@@ -18,6 +18,12 @@ def to_sql(arel, binds = [])
         end
       end
 
+      # This is used in the StatementCache object. It returns an object that
+      # can be used to query the database repeatedly.
+      def cacheable_query(arel) # :nodoc:
+        ActiveRecord::StatementCache.query self, visitor, arel.ast
+      end
+
       # Returns an ActiveRecord::Result instance.
       def select_all(arel, name = nil, binds = [])
         select(to_sql(arel, binds), name, binds)

activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb

@@ -44,6 +44,10 @@ def initialize(connection, logger, connection_options, config)
         configure_connection
       end
 
+      def cacheable_query(arel)
+        ActiveRecord::StatementCache.partial_query self, visitor, arel.ast
+      end
+
       MAX_INDEX_LENGTH_FOR_UTF8MB4 = 191
       def initialize_schema_migrations_table
         if @config[:encoding] == 'utf8mb4'

activerecord/lib/active_record/statement_cache.rb

@@ -16,6 +16,32 @@ module ActiveRecord
   class StatementCache
     Substitute = Struct.new :name
 
+    class Query
+      def initialize(connection, sql)
+        @connection = connection
+        @sql = sql
+      end
+
+      def sql_for(binds)
+        @sql
+      end
+    end
+
+    class PartialQuery < Query
+      def sql_for(binds)
+        @sql.gsub(/\?/) { @connection.quote(*binds.shift.reverse) }
+      end
+    end
+
+    def self.query(connection, visitor, ast)
+      Query.new connection, visitor.accept(ast)
+    end
+
+    def self.partial_query(connection, visitor, ast)
+      sql = visitor.accept(ast) { "?" }
+      PartialQuery.new connection, sql
+    end
+
     class Params
       def [](name); Substitute.new name; end
     end
@@ -45,17 +71,22 @@ def initialize(block = Proc.new)
       @sql      = nil
       @binds    = nil
       @block    = block
+      @query_builder = nil
       @params   = Params.new
     end
 
     def execute(params)
       rel = relation @params
 
-      arel  = rel.arel
-      klass = rel.klass
-      bv    = binds rel
+      arel        = rel.arel
+      klass       = rel.klass
+      bind_map    = binds rel
+      bind_values = bind_map.bind params
 
-      klass.find_by_sql sql(klass, arel, bv), bv.bind(params)
+      builder = query_builder klass.connection, arel
+      sql = builder.sql_for bind_values
+
+      klass.find_by_sql sql, bind_values
     end
     alias :call :execute
 
@@ -64,6 +95,12 @@ def binds(rel)
       @binds || @mutex.synchronize { @binds ||= BindMap.new rel.bind_values }
     end
 
+    def query_builder(connection, arel)
+      @query_builder || @mutex.synchronize {
+        @query_builder ||= connection.cacheable_query(arel)
+      }
+    end
+
     def sql(klass, arel, bv)
       @sql || @mutex.synchronize {
         @sql ||= klass.connection.to_sql arel, bv

activerecord/test/cases/statement_cache_test.rb

@@ -7,7 +7,6 @@
 module ActiveRecord
   class StatementCacheTest < ActiveRecord::TestCase
     def setup
-      skip if current_adapter?(:Mysql2Adapter)
       @connection = ActiveRecord::Base.connection
     end