- Do not load the adapter unless it is the current one in use

- Extract mysql foreign key definitions into the sql_2003 specification
- Add postgressql support, sans schema dumping. I will add foreign_keys to schema.rb soon.

lib/foreigner.rb

@@ -1,17 +1,12 @@
 require 'foreigner/connection_adapters/abstract/schema_statements'
 require 'foreigner/connection_adapters/abstract/schema_definitions'
-require 'foreigner/connection_adapters/mysql_adapter'
 require 'foreigner/schema_dumper'
 
 module ActiveRecord
   module ConnectionAdapters
     AbstractAdapter.class_eval do
       include Foreigner::AdapterMethods
     end
-
-    MysqlAdapter.class_eval do
-      include Foreigner::MysqlAdapter
-    end
 
     TableDefinition.class_eval do
       include Foreigner::TableDefinition
@@ -25,4 +20,10 @@ module ConnectionAdapters
   SchemaDumper.class_eval do
     include Foreigner::SchemaDumper
   end
+
+  Base.class_eval do
+    if ['MySQL', 'PostgreSQL'].include? connection.adapter_name
+      require "foreigner/connection_adapters/#{connection.adapter_name.downcase}_adapter"
+    end
+  end
 end

lib/foreigner/connection_adapters/mysql_adapter.rb

@@ -1,84 +1,46 @@
-module Foreigner
-  module MysqlAdapter
-    def supports_foreign_keys?
-      true
-    end
-
-    def add_foreign_key(from_table, to_table, options = {})
-      column  = options[:column] || "#{to_table.to_s.singularize}_id"
-      foreign_key_name = foreign_key_name(from_table, column, options)
+require 'foreigner/connection_adapters/sql_2003'
 
-      sql =
-        "ALTER TABLE #{quote_table_name(from_table)} " +
-        "ADD CONSTRAINT #{quote_column_name(foreign_key_name)} " +
-        foreign_key_definition(to_table, options)
+module Foreigner
+  module ConnectionAdapters
+    module MysqlAdapter
+      include Foreigner::ConnectionAdapters::Sql2003
 
-      execute(sql)
-    end
-
-    def foreign_key_definition(to_table, options = {})
-      column  = options[:column] || "#{to_table.to_s.singularize}_id"
-      dependency = dependency_sql(options[:dependent])
-
-      sql = "FOREIGN KEY (#{quote_column_name(column)}) REFERENCES #{quote_table_name(to_table)}(id)"
-      sql << " #{dependency}" unless dependency.blank?
-      sql
-    end
-
-    def remove_foreign_key(table, options)
-      if Hash === options
-        foreign_key_name = foreign_key_name(table, options[:column], options)
-      else
-        foreign_key_name = foreign_key_name(table, "#{options.to_s.singularize}_id")
-      end
-
-      execute "ALTER TABLE #{quote_table_name(table)} DROP FOREIGN KEY #{quote_column_name(foreign_key_name)}"
-    end
-
-    def foreign_keys(table_name)
-      foreign_keys = []
-      fk_info = select_all %{
-        SELECT fk.referenced_table_name as 'to_table'
-              ,fk.column_name as 'column'
-              ,fk.constraint_name as 'name'
-        FROM information_schema.key_column_usage fk
-        WHERE fk.referenced_column_name is not null
-          AND fk.table_schema = '#{@config[:database]}'
-          AND fk.table_name = '#{table_name}'
-      }
-
-      create_table_info = select_one("SHOW CREATE TABLE #{quote_table_name(table_name)}")["Create Table"]
-
-      fk_info.each do |row|
-        options = {:column => row['column'], :name => row['name']}
-        if create_table_info =~ /CONSTRAINT #{quote_column_name(row['name'])} FOREIGN KEY .* REFERENCES .* ON DELETE (CASCADE|SET NULL)/
-          if $1 == 'CASCADE'
-            options[:dependent] = :delete
-          elsif $1 == 'SET NULL'
-            options[:dependent] = :nullify
+      def foreign_keys(table_name)
+        foreign_keys = []
+        fk_info = select_all %{
+          SELECT fk.referenced_table_name as 'to_table'
+                ,fk.column_name as 'column'
+                ,fk.constraint_name as 'name'
+          FROM information_schema.key_column_usage fk
+          WHERE fk.referenced_column_name is not null
+            AND fk.table_schema = '#{@config[:database]}'
+            AND fk.table_name = '#{table_name}'
+        }
+
+        create_table_info = select_one("SHOW CREATE TABLE #{quote_table_name(table_name)}")["Create Table"]
+
+        fk_info.each do |row|
+          options = {:column => row['column'], :name => row['name']}
+          if create_table_info =~ /CONSTRAINT #{quote_column_name(row['name'])} FOREIGN KEY .* REFERENCES .* ON DELETE (CASCADE|SET NULL)/
+            if $1 == 'CASCADE'
+              options[:dependent] = :delete
+            elsif $1 == 'SET NULL'
+              options[:dependent] = :nullify
+            end
           end
+          foreign_keys << ForeignKeyDefinition.new(table_name, row['to_table'], options)
         end
-        foreign_keys << ForeignKeyDefinition.new(table_name, row['to_table'], options)
-      end
 
-      foreign_keys
-    end
-
-    private
-      def foreign_key_name(table, column, options = {})
-        if options[:name]
-          options[:name]
-        else
-          "#{table}_#{column}_fk"
-        end
+        foreign_keys
       end
+    end
+  end
+end
 
-      def dependency_sql(dependency)
-        case dependency
-          when :nullify then "ON DELETE SET NULL"
-          when :delete  then "ON DELETE CASCADE"
-          else ""
-        end
-      end
+module ActiveRecord
+  module ConnectionAdapters
+    MysqlAdapter.class_eval do
+      include Foreigner::ConnectionAdapters::MysqlAdapter
+    end
   end
 end

lib/foreigner/connection_adapters/postgresql_adapter.rb

@@ -0,0 +1,21 @@
+require 'foreigner/connection_adapters/sql_2003'
+
+module Foreigner
+  module ConnectionAdapters
+    module PostgreSQLAdapter
+      include Foreigner::ConnectionAdapters::Sql2003
+
+      def foreign_keys(table_name)
+
+      end
+    end
+  end
+end
+
+module ActiveRecord
+  module ConnectionAdapters
+    PostgreSQLAdapter.class_eval do
+      include Foreigner::ConnectionAdapters::PostgreSQLAdapter
+    end
+  end
+end

lib/foreigner/connection_adapters/sql_2003.rb

@@ -0,0 +1,57 @@
+module Foreigner
+  module ConnectionAdapters
+    module Sql2003
+      def supports_foreign_keys?
+        true
+      end
+
+      def add_foreign_key(from_table, to_table, options = {})
+        column  = options[:column] || "#{to_table.to_s.singularize}_id"
+        foreign_key_name = foreign_key_name(from_table, column, options)
+
+        sql =
+          "ALTER TABLE #{quote_table_name(from_table)} " +
+          "ADD CONSTRAINT #{quote_column_name(foreign_key_name)} " +
+          foreign_key_definition(to_table, options)
+
+        execute(sql)
+      end
+
+      def foreign_key_definition(to_table, options = {})
+        column  = options[:column] || "#{to_table.to_s.singularize}_id"
+        dependency = dependency_sql(options[:dependent])
+
+        sql = "FOREIGN KEY (#{quote_column_name(column)}) REFERENCES #{quote_table_name(to_table)}(id)"
+        sql << " #{dependency}" unless dependency.blank?
+        sql
+      end
+
+      def remove_foreign_key(table, options)
+        if Hash === options
+          foreign_key_name = foreign_key_name(table, options[:column], options)
+        else
+          foreign_key_name = foreign_key_name(table, "#{options.to_s.singularize}_id")
+        end
+
+        execute "ALTER TABLE #{quote_table_name(table)} DROP FOREIGN KEY #{quote_column_name(foreign_key_name)}"
+      end
+
+      private
+        def foreign_key_name(table, column, options = {})
+          if options[:name]
+            options[:name]
+          else
+            "#{table}_#{column}_fk"
+          end
+        end
+
+        def dependency_sql(dependency)
+          case dependency
+            when :nullify then "ON DELETE SET NULL"
+            when :delete  then "ON DELETE CASCADE"
+            else ""
+          end
+        end
+    end
+  end
+end