title: How to use H2 as embedded database in Postgres-compat mode, from jruby/rails
body: <p>I'd like to launch a jruby/rails app to use Postgres.  But I'd like to use H2 in Postgres compatibility mode when running in development and test.</p>
  
  <p>Its no problem bringing up the app in H2, or in postgresql, but how do I configure to run the postgresql adaptor, using an embedded H2 database?</p>
  
  <p>For example: something like this:</p>
  
  <p>database.yml</p>
  
  <pre><code>    development:
      #  adapter: jdbch2
      #  database: db/development/database
        adapter: postgresql
        encoding: unicode
        database: database
      #  driver: org.h2.Driver
        url: jdbc:h2:~/db/development;MODE=PostgreSQL
  
      test:
      ...
  </code></pre>
  
  <p>Gemfile:</p>
  
  <pre><code>...
  gem 'activerecord-jdbch2-adapter'
  #gem 'jdbc-h2'
  gem 'activerecord-jdbcpostgresql-adapter'
  ...
  </code></pre>