Load database adapters on demand. Eliminates config.connection_adapters and RAILS_CONNECTION_ADAPTERS. Closes #8456.

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@6833 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activerecord/CHANGELOG

@@ -1,5 +1,7 @@
 *SVN*
 
+* Load database adapters on demand. Eliminates config.connection_adapters and RAILS_CONNECTION_ADAPTERS. Add your lib directory to the $LOAD_PATH and put your custom adapter in lib/active_record/connection_adapters/adaptername_adapter.rb. This way you can provide custom adapters as plugins or gems without modifying Rails. [Jeremy Kemper]
+
 * Ensure that associations with :dependent => :delete_all respect :conditions option.  Closes #8034 [danger, joshpeek, Rick]
 
 * belongs_to assignment creates a new proxy rather than modifying its target in-place.  #8412 [mmangino@elevatedrails.com]

activerecord/lib/active_record.rb

@@ -73,13 +73,7 @@ ActiveRecord::Base.class_eval do
   include ActiveRecord::AttributeMethods
 end
 
-unless defined?(RAILS_CONNECTION_ADAPTERS)
-  RAILS_CONNECTION_ADAPTERS = %w( mysql postgresql sqlite firebird sqlserver db2 oracle sybase openbase frontbase )
-end
-
-RAILS_CONNECTION_ADAPTERS.each do |adapter|
-  require "active_record/connection_adapters/" + adapter + "_adapter"
-end
+require 'active_record/connection_adapters/abstract_adapter'
 
 require 'active_record/query_cache'
 require 'active_record/schema_dumper'

activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb

@@ -207,7 +207,12 @@ module ActiveRecord
           spec = spec.symbolize_keys
           unless spec.key?(:adapter) then raise AdapterNotSpecified, "database configuration does not specify adapter" end
           adapter_method = "#{spec[:adapter]}_connection"
-          unless respond_to?(adapter_method) then raise AdapterNotFound, "database configuration specifies nonexistent #{spec[:adapter]} adapter" end
+
+          require "active_record/connection_adapters/#{spec[:adapter]}_adapter"
+          unless respond_to?(adapter_method)
+            raise AdapterNotFound, "database configuration specifies nonexistent #{spec[:adapter]} adapter"
+          end
+
           remove_connection
           establish_connection(ConnectionSpecification.new(spec, adapter_method))
       end

activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb

@@ -0,0 +1,34 @@
+require 'active_record/connection_adapters/sqlite_adapter'
+
+module ActiveRecord
+  class Base
+    # sqlite3 adapter reuses sqlite_connection.
+    def self.sqlite3_connection(config) # :nodoc:
+      parse_sqlite_config!(config)
+
+      unless self.class.const_defined?(:SQLite3)
+        require_library_or_gem(config[:adapter])
+      end
+
+      db = SQLite3::Database.new(
+        config[:database],
+        :results_as_hash => true,
+        :type_translation => false
+      )
+
+      db.busy_timeout(config[:timeout]) unless config[:timeout].nil?
+
+      ConnectionAdapters::SQLite3Adapter.new(db, logger)
+    end
+  end
+
+  module ConnectionAdapters #:nodoc:
+    class SQLite3Adapter < SQLiteAdapter # :nodoc:
+      def table_structure(table_name)
+        returning structure = @connection.table_info(table_name) do
+          raise(ActiveRecord::StatementInvalid, "Could not find table '#{table_name}'") if structure.empty?
+        end
+      end
+    end
+  end
+end

activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb

@@ -1,33 +1,11 @@
-# Author: Luke Holden <lholden@cablelan.net>
-# Updated for SQLite3: Jamis Buck <jamis@37signals.com>
-
 require 'active_record/connection_adapters/abstract_adapter'
 
 module ActiveRecord
   class Base
     class << self
-      # sqlite3 adapter reuses sqlite_connection.
-      def sqlite3_connection(config) # :nodoc:
-        parse_config!(config)
-
-        unless self.class.const_defined?(:SQLite3)
-          require_library_or_gem(config[:adapter])
-        end
-
-        db = SQLite3::Database.new(
-          config[:database],
-          :results_as_hash => true,
-          :type_translation => false
-        )
-
-        db.busy_timeout(config[:timeout]) unless config[:timeout].nil?
-
-        ConnectionAdapters::SQLite3Adapter.new(db, logger)
-      end
-
       # Establishes a connection to the database that's used by all Active Record objects
       def sqlite_connection(config) # :nodoc:
-        parse_config!(config)
+        parse_sqlite_config!(config)
 
         unless self.class.const_defined?(:SQLite)
           require_library_or_gem(config[:adapter])
@@ -47,7 +25,7 @@ module ActiveRecord
       end
 
       private
-        def parse_config!(config)
+        def parse_sqlite_config!(config)
           config[:database] ||= config[:dbfile]
           # Require database.
           unless config[:database]
@@ -381,14 +359,6 @@ module ActiveRecord
         end
     end
 
-    class SQLite3Adapter < SQLiteAdapter # :nodoc:
-      def table_structure(table_name)
-        returning structure = @connection.table_info(table_name) do
-          raise(ActiveRecord::StatementInvalid, "Could not find table '#{table_name}'") if structure.empty?
-        end
-      end
-    end
-
     class SQLite2Adapter < SQLiteAdapter # :nodoc:
       def supports_count_distinct? #:nodoc:
         false