1 files changed, 85 insertions, 21 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
index 95f254ddd2..92908d9599 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
@@ -4,9 +4,9 @@ gem 'mysql2', '~> 0.3.10'
 require 'mysql2'
 
 module ActiveRecord
-  class Base
+  module ConnectionHandling
     # Establishes a connection to the database that's used by all Active Record objects.
-    def self.mysql2_connection(config)
+    def mysql2_connection(config)
       config[:username] = 'root' if config[:username].nil?
 
       if Mysql2::Client.const_defined? :FOUND_ROWS
@@ -32,9 +32,14 @@ module ActiveRecord
 
       def initialize(connection, logger, connection_options, config)
         super
+        @visitor = BindSubstitution.new self
         configure_connection
       end
 
+      def supports_explain?
+        true
+      end
+
       # HELPER METHODS ===========================================
 
       def each_hash(result) # :nodoc:
@@ -61,10 +66,6 @@ module ActiveRecord
         @connection.escape(string)
       end
 
-      def substitute_at(column, index)
-        Arel.sql "\0"
-      end
-
       # CONNECTION MANAGEMENT ====================================
 
       def active?
@@ -76,6 +77,7 @@ module ActiveRecord
         disconnect!
         connect
       end
+      alias :reset! :reconnect!
 
       # Disconnects from the database if already connected.
       # Otherwise, this method does nothing.
@@ -86,12 +88,81 @@ module ActiveRecord
         end
       end
 
-      def reset!
-        disconnect!
-        connect
+      # DATABASE STATEMENTS ======================================
+
+      def explain(arel, binds = [])
+        sql     = "EXPLAIN #{to_sql(arel, binds.dup)}"
+        start   = Time.now
+        result  = exec_query(sql, 'EXPLAIN', binds)
+        elapsed = Time.now - start
+
+        ExplainPrettyPrinter.new.pp(result, elapsed)
       end
 
-      # DATABASE STATEMENTS ======================================
+      class ExplainPrettyPrinter # :nodoc:
+        # Pretty prints the result of a EXPLAIN in a way that resembles the output of the
+        # MySQL shell:
+        #
+        #   +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+
+        #   | id | select_type | table | type  | possible_keys | key     | key_len | ref   | rows | Extra       |
+        #   +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+
+        #   |  1 | SIMPLE      | users | const | PRIMARY       | PRIMARY | 4       | const |    1 |             |
+        #   |  1 | SIMPLE      | posts | ALL   | NULL          | NULL    | NULL    | NULL  |    1 | Using where |
+        #   +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+
+        #   2 rows in set (0.00 sec)
+        #
+        # This is an exercise in Ruby hyperrealism :).
+        def pp(result, elapsed)
+          widths    = compute_column_widths(result)
+          separator = build_separator(widths)
+
+          pp = []
+
+          pp << separator
+          pp << build_cells(result.columns, widths)
+          pp << separator
+
+          result.rows.each do |row|
+            pp << build_cells(row, widths)
+          end
+
+          pp << separator
+          pp << build_footer(result.rows.length, elapsed)
+
+          pp.join("\n") + "\n"
+        end
+
+        private
+
+        def compute_column_widths(result)
+          [].tap do |widths|
+            result.columns.each_with_index do |column, i|
+              cells_in_column = [column] + result.rows.map {|r| r[i].nil? ? 'NULL' : r[i].to_s}
+              widths << cells_in_column.map(&:length).max
+            end
+          end
+        end
+
+        def build_separator(widths)
+          padding = 1
+          '+' + widths.map {|w| '-' * (w + (padding*2))}.join('+') + '+'
+        end
+
+        def build_cells(items, widths)
+          cells = []
+          items.each_with_index do |item, i|
+            item = 'NULL' if item.nil?
+            justifier = item.is_a?(Numeric) ? 'rjust' : 'ljust'
+            cells << item.to_s.send(justifier, widths[i])
+          end
+          '| ' + cells.join(' | ') + ' |'
+        end
+
+        def build_footer(nrows, elapsed)
+          rows_label = nrows == 1 ? 'row' : 'rows'
+          "#{nrows} #{rows_label} in set (%.2f sec)" % elapsed
+        end
+      end
 
       # FIXME: re-enable the following once a "better" query_cache solution is in core
       #
@@ -146,8 +217,7 @@ module ActiveRecord
       # Returns an array of record hashes with the column names as keys and
       # column values as values.
       def select(sql, name = nil, binds = [])
-        binds = binds.dup
-        exec_query(sql.gsub("\0") { quote(*binds.shift.reverse) }, name).to_a
+        exec_query(sql, name)
       end
 
       def insert_sql(sql, name = nil, pk = nil, id_value = nil, sequence_name = nil)
@@ -156,18 +226,12 @@ module ActiveRecord
       end
       alias :create :insert_sql
 
-      def exec_insert(sql, name, binds)
-        binds = binds.dup
-
-        # Pretend to support bind parameters
-        execute sql.gsub("\0") { quote(*binds.shift.reverse) }, name
+      def exec_insert(sql, name, binds, pk = nil, sequence_name = nil)
+        execute to_sql(sql, binds), name
       end
 
       def exec_delete(sql, name, binds)
-        binds = binds.dup
-
-        # Pretend to support bind parameters
-        execute sql.gsub("\0") { quote(*binds.shift.reverse) }, name
+        execute to_sql(sql, binds), name
         @connection.affected_rows
       end
       alias :exec_update :exec_delete