Support updates with joins. Fixes #522.

3 files changed, 17 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
index 2ae655e68d..7543d35d3b 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
@@ -306,6 +306,15 @@ module ActiveRecord
         end
       end
 
+      # The default strategy for an UPDATE with joins is to use a subquery. This doesn't work
+      # on mysql (even when aliasing the tables), but mysql allows using JOIN directly in
+      # an UPDATE statement, so in the mysql adapters we redefine this to do that.
+      def join_to_update(update, select) #:nodoc:
+        subselect = select.clone
+        subselect.ast.cores.last.projections = [update.ast.key]
+        update.wheres = [update.ast.key.in(subselect)]
+      end
+
       protected
         # Returns an array of record hashes with the column names as keys and
         # column values as values.
diff --git a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
index 18fdfa29ec..c01a64e354 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
@@ -577,6 +577,10 @@ module ActiveRecord
         where_sql
       end
 
+      def join_to_update(update, select) #:nodoc:
+        update.table select.ast.cores.last.source
+      end
+
       protected
         def quoted_columns_for_index(column_names, options = {})
           length = options[:length] if options.is_a?(Hash)
diff --git a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
index 14b950dbb0..ea0970028c 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
@@ -491,6 +491,10 @@ module ActiveRecord
         execute("RELEASE SAVEPOINT #{current_savepoint_name}")
       end
 
+      def join_to_update(update, select) #:nodoc:
+        update.table select.ast.cores.last.source
+      end
+
       # SCHEMA STATEMENTS ========================================
 
       def structure_dump #:nodoc: