From: Brian Candler <B.Candler@...>
Date: 2003-03-27T20:02:49+09:00
Subject: [PATCH] transaction support for dbd_mysql


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The following patch adds transaction support to dbd_mysql, e.g.

  require 'dbi'
  db = DBI.connect('dbi:mysql:test','foo')
  db['AutoCommit'] = false
  db.execute('create table foo(bar varchar(200)) type=innodb') rescue nil

  db.transaction do
    p db.select_one('select count(*) from foo')
    db.execute('insert into foo values (?)','hello')
    p db.select_one('select count(*) from foo')
    raise "hell"   # does an automatic rollback
  end

It was rather too simple to implement, so I'm not sure if I'm missing
something fundamental here. I'd appreciate feedback from any other mysql
users.

I didn't implement the read accessor, e.g. "puts db['AutoCommit']", because
I can't find a way to ask mysql to show the current AutoCommit state, and I
don't believe that keeping a parallel instance variable is a good idea.

I had a quick look at how the pg driver implements transactions. It uses an
instance variable "@in_transaction", but this does not appear to be
necessary in mysql, as you don't need to issue an explicit 'BEGIN'.

I did notice one odd thing in the pg driver:

            if attr =~ /^pg_/ or attr != /_/
                                 ^^^^^^^^^^^

I think that should be "attr !~ /_/" otherwise I can't see how it does
anything useful.

Regards,

Brian.

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diff -uNr ruby-dbi-all.orig/lib/dbd_mysql/Mysql.rb ruby-dbi-all/lib/dbd_mysql/Mysql.rb
--- ruby-dbi-all.orig/lib/dbd_mysql/Mysql.rb	Thu Sep 26 19:37:27 2002
+++ ruby-dbi-all/lib/dbd_mysql/Mysql.rb	Wed Mar 26 18:46:46 2003
@@ -255,14 +255,20 @@
     Statement.new(self, @handle, statement, @mutex)
   end
 
-  # TODO: Raise Error
   def commit
+    mysql_do('commit')
   end
 
-  # TODO: Raise Error
   def rollback
+    mysql_do('rollback')
   end
 
+  def []=(attr, value)
+    case attr
+    when 'AutoCommit'
+      mysql_do('set autocommit=' + (value ? '1' : '0'))
+    end
+  end
 
   def quote(value)
     case value
@@ -276,6 +282,14 @@
   end
 
   private # -------------------------------------------------
+
+  def mysql_do(sql)
+    @mutex.synchronize { 
+      @handle.query_with_result = false
+      @handle.query(sql)
+    }
+    nil
+  end
 
   # Eli Green
   def mysql_type_info(typedef)

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