Implement CASE Conditional Expression

1 files changed, 57 insertions, 0 deletions

diff --git a/lib/arel/nodes/case.rb b/lib/arel/nodes/case.rb
new file mode 100644
index 0000000000..85f8851dbe
--- /dev/null
+++ b/lib/arel/nodes/case.rb
@@ -0,0 +1,57 @@
+module Arel
+  module Nodes
+    class Case < Arel::Nodes::Node
+      include Arel::OrderPredications
+      include Arel::Predications
+      include Arel::AliasPredication
+
+      attr_accessor :case, :conditions, :default
+
+      def initialize expression = nil, default = nil
+        @case = expression
+        @conditions = []
+        @default = default
+      end
+
+      def when condition, expression = nil
+        @conditions << When.new(Nodes.build_quoted(condition), expression)
+        self
+      end
+
+      def then expression
+        @conditions.last.right = Nodes.build_quoted(expression)
+        self
+      end
+
+      def else expression
+        @default = Else.new Nodes.build_quoted(expression)
+        self
+      end
+
+      def initialize_copy other
+        super
+        @case = @case.clone if @case
+        @conditions = @conditions.map { |x| x.clone }
+        @default = @default.clone if @default
+      end
+
+      def hash
+        [@case, @conditions, @default].hash
+      end
+
+      def eql? other
+        self.class == other.class &&
+          self.case == other.case &&
+          self.conditions == other.conditions &&
+          self.default == other.default
+      end
+      alias :== :eql?
+    end
+
+    class When < Binary # :nodoc:
+    end
+
+    class Else < Unary # :nodoc:
+    end
+  end
+end