requiring that the primary key be set on the UpdateManager so that databases which do not support UPDATE with LIMIT will work

lib/arel/crud.rb

@@ -6,7 +6,7 @@ module Arel
       um = UpdateManager.new @engine
 
       if Nodes::SqlLiteral === values
-        relation = @ctx.froms
+        relation = @ctx.from
       else
         relation = values.first.first.relation
       end

lib/arel/nodes/update_statement.rb

@@ -2,13 +2,15 @@ module Arel
   module Nodes
     class UpdateStatement < Arel::Nodes::Node
       attr_accessor :relation, :wheres, :values, :orders, :limit
+      attr_accessor :key
 
       def initialize
         @relation = nil
         @wheres   = []
         @values   = []
-        @orders = []
-        @limit  = nil
+        @orders   = []
+        @limit    = nil
+        @key      = nil
       end
 
       def initialize_copy other

lib/arel/update_manager.rb

@@ -11,6 +11,10 @@ module Arel
       self
     end
 
+    def key= key
+      @ast.key = key
+    end
+
     def order *expr
       @ast.orders = expr
       self

lib/arel/visitors/to_sql.rb

@@ -42,20 +42,31 @@ module Arel
         if o.orders.empty? && o.limit.nil?
           wheres = o.wheres
         else
+          key = o.key
+          unless key
+            warn(<<-eowarn) if $VERBOSE
+(#{caller.first}) Using UpdateManager without setting UpdateManager#key is
+deprecated and support will be removed in ARel 3.0.0.  Please set the primary
+key on UpdateManager using UpdateManager#key=
+eowarn
+            key = o.relation.primary_key
+          end
+
+          wheres = o.wheres
           stmt             = Nodes::SelectStatement.new
           core             = stmt.cores.first
           core.froms       = o.relation
-          core.projections = [o.relation.primary_key]
+          core.projections = [key]
           stmt.limit       = o.limit
           stmt.orders      = o.orders
 
-          wheres = [Nodes::In.new(o.relation.primary_key, [stmt])]
+          wheres = [Nodes::In.new(key, [stmt])]
         end
 
         [
           "UPDATE #{visit o.relation}",
           ("SET #{o.values.map { |value| visit value }.join ', '}" unless o.values.empty?),
-          ("WHERE #{wheres.map { |x| visit x }.join ' AND '}" unless wheres.empty?)
+          ("WHERE #{wheres.map { |x| visit x }.join ' AND '}" unless wheres.empty?),
         ].compact.join ' '
       end
 

test/test_select_manager.rb

@@ -480,6 +480,7 @@ module Arel
         manager.from table
         manager.take 1
         stmt = manager.compile_update(SqlLiteral.new('foo = bar'))
+        stmt.key = table['id']
 
         stmt.to_sql.must_be_like %{
           UPDATE "users" SET foo = bar
@@ -494,6 +495,7 @@ module Arel
         manager.from table
         manager.order :foo
         stmt = manager.compile_update(SqlLiteral.new('foo = bar'))
+        stmt.key = table['id']
 
         stmt.to_sql.must_be_like %{
           UPDATE "users" SET foo = bar