Add nodes for boolean constants

This is useful for dynamically created predicates e.g:

expr1 = table.create_false
expr2 = table.create_false

expr1 = create_a_predicate() if some_condition
expr2 = create_another_predicate() if some_other_condition

table.where(expr1.and(expr2))

6 files changed, 52 insertions, 1 deletions

diff --git a/lib/arel/factory_methods.rb b/lib/arel/factory_methods.rb
index 9fd0878ada..3b16feae10 100644
--- a/lib/arel/factory_methods.rb
+++ b/lib/arel/factory_methods.rb
@@ -2,6 +2,14 @@ module Arel
   ###
   # Methods for creating various nodes
   module FactoryMethods
+    def create_true
+      Arel::Nodes::True.new
+    end
+
+    def create_false
+      Arel::Nodes::False.new
+    end
+
     def create_table_alias relation, name
       Nodes::TableAlias.new(relation, name)
     end
diff --git a/lib/arel/nodes.rb b/lib/arel/nodes.rb
index 9edf3a9a95..e37b09a8ac 100644
--- a/lib/arel/nodes.rb
+++ b/lib/arel/nodes.rb
@@ -8,6 +8,8 @@ require 'arel/nodes/update_statement'
 # terminal
 
 require 'arel/nodes/terminal'
+require 'arel/nodes/true'
+require 'arel/nodes/false'
 
 # unary
 require 'arel/nodes/unary'
diff --git a/lib/arel/nodes/false.rb b/lib/arel/nodes/false.rb
new file mode 100644
index 0000000000..4196070946
--- /dev/null
+++ b/lib/arel/nodes/false.rb
@@ -0,0 +1,17 @@
+module Arel
+  module Nodes
+    class False < Arel::Nodes::Node
+      def not
+        True.new
+      end
+
+      def or right
+        right
+      end
+
+      def and right
+        self
+      end
+    end
+  end
+end
diff --git a/lib/arel/nodes/true.rb b/lib/arel/nodes/true.rb
new file mode 100644
index 0000000000..82f20837f8
--- /dev/null
+++ b/lib/arel/nodes/true.rb
@@ -0,0 +1,17 @@
+module Arel
+  module Nodes
+    class True < Arel::Nodes::Node
+      def not
+        False.new
+      end
+
+      def or right
+        self
+      end
+
+      def and right
+        right
+      end
+    end
+  end
+end
diff --git a/lib/arel/predications.rb b/lib/arel/predications.rb
index 4b124ce05c..e3f72d46a2 100644
--- a/lib/arel/predications.rb
+++ b/lib/arel/predications.rb
@@ -1,6 +1,5 @@
 module Arel
   module Predications
-
     def not_eq other
       Nodes::NotEqual.new self, other
     end
diff --git a/lib/arel/visitors/to_sql.rb b/lib/arel/visitors/to_sql.rb
index 933edc15f2..8aec4cb147 100644
--- a/lib/arel/visitors/to_sql.rb
+++ b/lib/arel/visitors/to_sql.rb
@@ -90,6 +90,14 @@ key on UpdateManager using UpdateManager#key=
           o.alias ? " AS #{visit o.alias}" : ''}"
       end
 
+      def visit_Arel_Nodes_True o
+        "TRUE"
+      end
+
+      def visit_Arel_Nodes_False o
+        "FALSE"
+      end
+
       def table_exists? name
         @pool.table_exists? name
       end