Issue

Can’t use merb sessions with datamapper & mysql, get back an error about needing an id on the text column or something (I had the error a couple of days ago.)

Solution

I suggest grabbing merb_datamapper svn source to fix this in. To do so make sure you have subversion installed on your machine (I’m assuming a Unix based machine here.)

1. Checkout the source

    svn co http://svn.devjavu.com/merb/plugins/merb_datamapper
   

2. Open up the affected file in your favourite editor (I use TextMate)

    cd merb_datamapper
    mate lib/merb/sessions/data_mapper_session.rb
   

3. Find line 25 that contains

    `property :session_id, :text, :lazy => false, :key => true`
   

   and remove :text, :lazy => false to replace it with :string

    `property :session_id, :string, :key => true`
   

   Save and close the file, thats the editing done. Now to install the gem.

4. Build the gem

    rake gem
   

5. Install the gem

    sudo gem install pkg/merb_datamapper-0.5.gem
   

And you’re away with the fix installed. Now just run merb to create your sessions table in the db. Hope this helped!