fk: `foreign_keys`, `add_foreign_key` and `remove_foreign_key` for MySQL

5 files changed, 65 insertions, 21 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
index a9b3e9cfb9..b132543332 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
@@ -25,6 +25,20 @@ module ActiveRecord
     class ChangeColumnDefinition < Struct.new(:column, :type, :options) #:nodoc:
     end
 
+    class ForeignKeyDefinition < Struct.new(:from_table, :to_table, :options)
+      def name
+        options[:name]
+      end
+
+      def column
+        options[:column]
+      end
+
+      def primary_key
+        options[:primary_key]
+      end
+    end
+
     # Represents the schema of an SQL table in an abstract way. This class
     # provides methods for manipulating the schema representation.
     #
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
index 22823a8c58..55e3fb4477 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -625,6 +625,13 @@ module ActiveRecord
       end
       alias :add_belongs_to :add_reference
 
+      def foreign_key_name(table_name, options)
+        options.fetch(:name) do
+          column_name = options.fetch(:column)
+          "#{table_name}_#{column_name}_fk"
+        end
+      end
+
       # Removes the reference(s). Also removes a +type+ column if one exists.
       # <tt>remove_reference</tt>, <tt>remove_references</tt> and <tt>remove_belongs_to</tt> are acceptable.
       #
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index def04dbed2..431db591e6 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -192,6 +192,10 @@ module ActiveRecord
         true
       end
 
+      def supports_foreign_keys?
+        true
+      end
+
       def native_database_types
         NATIVE_DATABASE_TYPES
       end
@@ -501,6 +505,46 @@ module ActiveRecord
         execute "CREATE #{index_type} INDEX #{quote_column_name(index_name)} #{index_using} ON #{quote_table_name(table_name)} (#{index_columns})#{index_options} #{index_algorithm}"
       end
 
+      def foreign_keys(table_name)
+        fk_info = select_all %{
+          SELECT fk.referenced_table_name as 'to_table'
+                ,fk.referenced_column_name as 'primary_key'
+                ,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.map do |row|
+          options = {column: row['column'], name: row['name'], primary_key: row['primary_key']}
+          ForeignKeyDefinition.new(table_name, row['to_table'], options)
+        end
+      end
+
+      def add_foreign_key(from_table, to_table, options = {})
+        foreign_key_column = options.fetch(:column)
+        referenced_column = "id"
+        foreign_key_name = foreign_key_name(from_table, options)
+        execute <<-SQL
+ALTER TABLE #{quote_table_name(from_table)}
+ADD CONSTRAINT #{foreign_key_name}
+FOREIGN KEY (#{quote_column_name(foreign_key_column)})
+REFERENCES #{quote_table_name(to_table)} (#{quote_column_name(referenced_column)})
+        SQL
+      end
+
+      def remove_foreign_key(from_table, options = {})
+        foreign_key_name = foreign_key_name(from_table, options)
+        execute <<-SQL
+ALTER TABLE #{quote_table_name(from_table)}
+DROP FOREIGN KEY #{foreign_key_name}
+        SQL
+      end
+
       # Maps logical Rails types to MySQL-specific data types.
       def type_to_sql(type, limit = nil, precision = nil, scale = nil)
         case type.to_s
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb
index 724e3fa1ee..0867e5ef54 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb
@@ -89,20 +89,6 @@ module ActiveRecord
         attr_accessor :array
       end
 
-      class ForeignKeyDefinition < Struct.new(:from_table, :to_table, :options)
-        def name
-          options[:name]
-        end
-
-        def column
-          options[:column]
-        end
-
-        def primary_key
-          options[:primary_key]
-        end
-      end
-
       class TableDefinition < ActiveRecord::ConnectionAdapters::TableDefinition
         include ColumnMethods
 
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
index b87fb85ae2..7a93d9cde7 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
@@ -492,13 +492,6 @@ DROP CONSTRAINT #{foreign_key_name}
           SQL
         end
 
-        def foreign_key_name(table_name, options)
-          options.fetch(:name) do
-            column_name = options.fetch(:column)
-            "#{table_name}_#{column_name}_fk"
-          end
-        end
-
         def index_name_length
           63
         end