set.rb in veritas-sql-generator-0.0.4

- old
+ new

@@ -10,10 +10,31 @@
 
           DIFFERENCE   = 'EXCEPT'.freeze
           INTERSECTION = 'INTERSECT'.freeze
           UNION        = 'UNION'.freeze
 
+          # Normalize the headers of the operands
+          #
+          # This is necessary to make sure the columns are in the correct
+          # order when generating SQL.
+          #
+          # @param [Relation::Operation::Set] relation
+          #
+          # @return [Relation::Operation::Set]
+          #
+          # @api private
+          def self.normalize_operand_headers(relation)
+            left        = relation.left
+            right       = relation.right
+            left_header = left.header
+            if left_header.to_a != right.header.to_a
+              relation.class.new(left, right.project(left_header))
+            else
+              relation
+            end
+          end
+
           # Visit a Union
           #
           # @param [Algebra::Union] union
           #
           # @return [self]
@@ -52,42 +73,29 @@
             set_operands(difference)
             set_name
             self
           end
 
-          # Return the SQL for the set relation
-          #
-          # @example
-          #   sql = set_relation.to_s
-          #
-          # @return [#to_s]
-          #
-          # @api public
-          def to_s
-            generate_sql(:to_s)
-          end
+        private
 
-          # Return the SQL suitable for an subquery
+          # Generate the SQL using the supplied method
           #
           # @return [#to_s]
           #
           # @api private
-          def to_subquery
-            generate_sql(:to_subquery)
+          def generate_sql(*)
+            "(#{@left}) #{@operation} (#{@right})"
           end
 
-        private
-
-          # Generate the SQL using the supplied method
+          # Set the operands from the relation
           #
-          # @param [Symbol] method
+          # @param [Relation::Operation::Set] relation
           #
-          # @return [#to_s]
+          # @return [undefined]
           #
           # @api private
-          def generate_sql(method)
-            return EMPTY_STRING unless visited?
-            "(#{@left.send(method)}) #{@operation} (#{@right.send(method)})"
+          def set_operands(relation)
+            super self.class.normalize_operand_headers(relation)
           end
 
           # Generates an SQL statement for base relation set operands
           class Base < Relation::Base; end
 