Merge pull request #8 from localytics/null-adapter

Null adapter

README.md

@@ -4,7 +4,7 @@
 
 An ActiveRecord ODBC adapter. Master branch is working off of edge Rails. Previous work has been done to make it compatible with Rails 3.2 and 4.2; for those versions use the 3.2.x or 4.2.x gem releases.
 
-This adapter currently works for connecting using ODBC to MySQL 5 and PostgreSQL 9 databases. You can also register your own adapter using the `ODBCAdapter.register` function to connect to a database of your choice.
+This adapter will work for basic queries for most DBMSs out of the box, without support for migrations. Full support is built-in for MySQL 5 and PostgreSQL 9 databases. You can register your own adapter to get more support for your DBMS using the `ODBCAdapter.register` function.
 
 A lot of this work is based on [OpenLink's ActiveRecord adapter](http://odbc-rails.rubyforge.org/) which works for earlier versions of Rails.
 

lib/odbc_adapter/adapters/null_odbc_adapter.rb

@@ -0,0 +1,31 @@
+module ODBCAdapter
+  module Adapters
+    # A default adapter used for databases that are no explicitly listed in the
+    # registry. This allows for minimal support for DBMSs for which we don't
+    # have an explicit adapter.
+    class NullODBCAdapter < ActiveRecord::ConnectionAdapters::ODBCAdapter
+      class BindSubstitution < Arel::Visitors::ToSql
+        include Arel::Visitors::BindVisitor
+      end
+
+      # Using a BindVisitor so that the SQL string gets substituted before it is
+      # sent to the DBMS (to attempt to get as much coverage as possible for
+      # DBMSs we don't support).
+      def arel_visitor
+        BindSubstitution.new(self)
+      end
+
+      # Explicitly turning off prepared_statements in the null adapter because
+      # there isn't really a standard on which substitution character to use.
+      def prepared_statements
+        false
+      end
+
+      # Turning off support for migrations because there is no information to
+      # go off of for what syntax the DBMS will expect.
+      def supports_migrations?
+        false
+      end
+    end
+  end
+end

lib/odbc_adapter/registry.rb

@@ -16,8 +16,7 @@ def adapter_for(reported_name)
           adapter if reported_name =~ pattern
         end
 
-      raise ArgumentError, "ODBCAdapter: Unsupported database (#{reported_name})" if found.nil?
-      normalize_adapter(found.last)
+      normalize_adapter(found && found.last || :Null)
     end
 
     def register(pattern, superclass = Object, &block)