adding an EXISTS node, update method will generate an IN clause

6 files changed, 36 insertions, 4 deletions

diff --git a/lib/arel/crud.rb b/lib/arel/crud.rb
index b1269bd1da..196dc56554 100644
--- a/lib/arel/crud.rb
+++ b/lib/arel/crud.rb
@@ -7,12 +7,23 @@ module Arel
       um = UpdateManager.new @engine
 
       if Nodes::SqlLiteral === values
-        um.table @ctx.froms.last
+        relation = @ctx.froms.last
       else
-        um.table values.first.first.relation
+        relation = values.first.first.relation
       end
+      um.table relation
       um.set values
-      um.wheres = @ctx.wheres
+
+      if @head.orders.empty? && @head.limit.nil?
+        um.wheres = @ctx.wheres
+      else
+        head             = @head.clone
+        core             = head.cores.first
+        core.projections = [relation.primary_key]
+
+        um.wheres = [Nodes::In.new(relation.primary_key, [head])]
+      end
+
       @engine.connection.update um.to_sql, 'AREL'
     end
 
diff --git a/lib/arel/nodes.rb b/lib/arel/nodes.rb
index 3ffc81d7df..99a34c3b2b 100644
--- a/lib/arel/nodes.rb
+++ b/lib/arel/nodes.rb
@@ -14,6 +14,7 @@ require 'arel/nodes/count'
 require 'arel/nodes/values'
 require 'arel/nodes/offset'
 require 'arel/nodes/sum'
+require 'arel/nodes/exists'
 require 'arel/nodes/max'
 require 'arel/nodes/min'
 require 'arel/nodes/avg'
diff --git a/lib/arel/nodes/exists.rb b/lib/arel/nodes/exists.rb
new file mode 100644
index 0000000000..167a345006
--- /dev/null
+++ b/lib/arel/nodes/exists.rb
@@ -0,0 +1,11 @@
+module Arel
+  module Nodes
+    class Exists
+      attr_reader :select_stmt
+
+      def initialize select_stmt
+        @select_stmt = select_stmt
+      end
+    end
+  end
+end
diff --git a/lib/arel/nodes/select_statement.rb b/lib/arel/nodes/select_statement.rb
index 6272fd126d..637ba5d1d0 100644
--- a/lib/arel/nodes/select_statement.rb
+++ b/lib/arel/nodes/select_statement.rb
@@ -14,7 +14,7 @@ module Arel
 
       def initialize_copy other
         super
-        @cores = @cores.clone
+        @cores = @cores.map { |x| x.clone }
       end
     end
   end
diff --git a/lib/arel/table.rb b/lib/arel/table.rb
index 1519efa63b..06bbe7b99e 100644
--- a/lib/arel/table.rb
+++ b/lib/arel/table.rb
@@ -14,6 +14,7 @@ module Arel
       @columns = nil
       @aliases = []
       @table_alias = nil
+      @primary_key = nil
 
       # Sometime AR sends an :as parameter to table, to let the table know that
       # it is an Alias.  We may want to override new, and return a TableAlias
@@ -21,6 +22,10 @@ module Arel
       @table_alias = engine[:as] if Hash === engine
     end
 
+    def primary_key
+      @primary_key ||= self[@engine.connection.primary_key(name)]
+    end
+
     def alias
       Nodes::TableAlias.new("#{name}_2", self).tap do |node|
         @aliases << node
diff --git a/lib/arel/visitors/to_sql.rb b/lib/arel/visitors/to_sql.rb
index 2660c7d284..dc65e86219 100644
--- a/lib/arel/visitors/to_sql.rb
+++ b/lib/arel/visitors/to_sql.rb
@@ -41,6 +41,10 @@ module Arel
         ].compact.join ' '
       end
 
+      def visit_Arel_Nodes_Exists o
+        "EXISTS (#{visit o.select_stmt})"
+      end
+
       def visit_Arel_Nodes_Values o
         "VALUES (#{o.expressions.map { |value|
           value.nil? ? 'NULL' : visit(value)