Add database specific string concatenation

lib/arel/nodes/infix_operation.rb

@@ -40,5 +40,10 @@ def initialize left, right
       end
     end
 
+    class Concat < InfixOperation
+      def initialize left, right
+        super('||', left, right)
+      end
+    end
   end
-end
+end

lib/arel/predications.rb

@@ -202,6 +202,10 @@ def when right
       Nodes::Case.new(self).when quoted_node(right)
     end
 
+    def concat other
+      Nodes::Concat.new self, other
+    end
+
     private
 
     def grouping_any method_id, others, *extras

lib/arel/visitors/depth_first.rb

@@ -72,6 +72,7 @@ def binary o
       alias :visit_Arel_Nodes_As                 :binary
       alias :visit_Arel_Nodes_Assignment         :binary
       alias :visit_Arel_Nodes_Between            :binary
+      alias :visit_Arel_Nodes_Concat             :binary
       alias :visit_Arel_Nodes_DeleteStatement    :binary
       alias :visit_Arel_Nodes_DoesNotMatch       :binary
       alias :visit_Arel_Nodes_Equality           :binary

lib/arel/visitors/dot.rb

@@ -176,6 +176,7 @@ def binary o
       alias :visit_Arel_Nodes_As                 :binary
       alias :visit_Arel_Nodes_Assignment         :binary
       alias :visit_Arel_Nodes_Between            :binary
+      alias :visit_Arel_Nodes_Concat             :binary
       alias :visit_Arel_Nodes_DoesNotMatch       :binary
       alias :visit_Arel_Nodes_Equality           :binary
       alias :visit_Arel_Nodes_GreaterThan        :binary

lib/arel/visitors/mysql.rb

@@ -72,6 +72,14 @@ def visit_Arel_Nodes_UpdateStatement o, collector
         maybe_visit o.limit, collector
       end
 
+      def visit_Arel_Nodes_Concat o, collector
+        collector << " CONCAT("
+        visit o.left, collector
+        collector << ", "
+        visit o.right, collector
+        collector << ") "
+        collector
+      end
     end
   end
 end

test/visitors/test_depth_first.rb

@@ -103,6 +103,7 @@ def test_right_outer_join
       [
         Arel::Nodes::Assignment,
         Arel::Nodes::Between,
+        Arel::Nodes::Concat,
         Arel::Nodes::DoesNotMatch,
         Arel::Nodes::Equality,
         Arel::Nodes::GreaterThan,

test/visitors/test_mysql.rb

@@ -55,6 +55,24 @@ def compile node
           compile(node).must_be_like "LOCK IN SHARE MODE"
         end
       end
+
+      describe "concat" do
+        it "concats columns" do
+          @table = Table.new(:users)
+          query = @table[:name].concat(@table[:name])
+          compile(query).must_be_like %{
+            CONCAT("users"."name", "users"."name")
+          }
+        end
+
+        it "concats a string" do
+          @table = Table.new(:users)
+          query = @table[:name].concat(Nodes.build_quoted('abc'))
+          compile(query).must_be_like %{
+            CONCAT("users"."name", 'abc')
+          }
+        end
+      end
     end
   end
 end

test/visitors/test_to_sql.rb

@@ -469,13 +469,19 @@ def quote value, column = nil
           compile(node).must_equal %(("products"."price" - 7))
         end
 
+        it "should handle Concatination" do
+          table = Table.new(:users)
+          node = table[:name].concat(table[:name])
+          compile(node).must_equal %("users"."name" || "users"."name")
+        end
+
         it "should handle arbitrary operators" do
           node = Arel::Nodes::InfixOperation.new(
-            '||',
+            '&&',
             Arel::Attributes::String.new(Table.new(:products), :name),
             Arel::Attributes::String.new(Table.new(:products), :name)
           )
-          compile(node).must_equal %("products"."name" || "products"."name")
+          compile(node).must_equal %("products"."name" && "products"."name")
         end
       end