lib/veritas/sql/generator/relation.rb in veritas-sql-generator-0.0.3 vs lib/veritas/sql/generator/relation.rb in veritas-sql-generator-0.0.4

@@ -9,11 +9,12 @@
         extend Identifier
         include Attribute
 
         EMPTY_STRING = ''.freeze
         SEPARATOR    = ', '.freeze
-        ALL_COLUMNS  = '*'.freeze
+        STAR         = '*'.freeze
+        EMPTY_HASH   = {}.freeze
 
         # Return the alias name
         #
         # @return [#to_s]
         #
@@ -30,38 +31,25 @@
         def self.visit(relation)
           klass = case relation
             when Veritas::Relation::Operation::Set    then self::Set
             when Veritas::Relation::Operation::Binary then self::Binary
             when Veritas::Relation::Operation::Unary  then self::Unary
-            when Veritas::BaseRelation                then self::Base
+            when Veritas::Relation::Base              then self::Base
             else
               raise InvalidRelationError, "#{relation.class} is not a visitable relation"
           end
           klass.new.visit(relation)
         end
 
-        # Return the subquery for the relation and identifier
-        #
-        # @param [#to_subquery] relation
-        #
-        # @param [#to_s] identifier
-        #   optional identifier, defaults to relation.name
-        #
-        # @return [#to_s]
-        #
-        # @api private
-        def self.subquery(relation, identifier = relation.name)
-          "(#{relation.to_subquery}) AS #{visit_identifier(identifier)}"
-        end
-
         # Initialize a Generator
         #
         # @return [undefined]
         #
         # @api private
         def initialize
-          @sql = EMPTY_STRING
+          @sql        = EMPTY_STRING
+          @extensions = {}
         end
 
         # Visit an object and generate SQL from each node
         #
         # @example
@@ -91,19 +79,158 @@
         # @api public
         def to_sql
           @sql
         end
 
+        # Return the SQL for the unary relation
+        #
+        # @example
+        #   sql = unary_relation.to_s
+        #
+        # @return [#to_s]
+        #
+        # @api public
+        def to_s
+          return EMPTY_STRING unless visited?
+          generate_sql(query_columns)
+        end
+
+        # Return the SQL suitable for an subquery
+        #
+        # @return [#to_s]
+        #
+        # @api private
+        def to_subquery
+          return EMPTY_STRING unless visited?
+          Generator.parenthesize!(generate_sql(subquery_columns))
+        end
+
         # Test if a visitable object has been visited
         #
         # @example
         #   visitor.visited?  # true or false
         #
         # @return [Boolean]
         #
         # @api public
         def visited?
           !@name.nil?
+        end
+
+      private
+
+        # Return the columns to use in a query
+        #
+        # @return [#to_s]
+        #
+        # @api private
+        def query_columns
+          explicit_columns
+        end
+
+        # Return the columns to use in a subquery
+        #
+        # @return [#to_s]
+        #
+        # @api private
+        def subquery_columns
+          implicit_columns
+        end
+
+        # Return the implicit columns for the select list
+        #
+        # @return [#to_s]
+        #
+        # @api private
+        def implicit_columns
+          sql = [ STAR, column_list_for(@extensions) ]
+          sql.reject! { |fragment| fragment.empty? }
+          sql.join(SEPARATOR)
+        end
+
+        # Return the explicit columns for the select list
+        #
+        # @return [#to_s]
+        #
+        # @api private
+        def explicit_columns
+          @distinct.to_s + column_list_for(@extensions.merge(@columns || EMPTY_HASH))
+        end
+
+        # Return the list of columns
+        #
+        # @param [#map] columns
+        #
+        # @return [#to_s]
+        #
+        # @api private
+        def column_list_for(columns)
+          sql = columns.values_at(*@header)
+          sql.compact!
+          sql.join(SEPARATOR)
+        end
+
+        # Return a list of columns in a header
+        #
+        # @param [Veritas::Relation] relation
+        #
+        # @param [#[]] aliases
+        #   optional aliases for the columns
+        #
+        # @return [Hash]
+        #
+        # @api private
+        def columns_for(relation, aliases = EMPTY_HASH)
+          columns = {}
+          relation.header.each do |attribute|
+            columns[aliases.fetch(attribute, attribute)] = column_for(attribute, aliases)
+          end
+          columns
+        end
+
+        # Return the column for an attribute
+        #
+        # @param [Attribute] attribute
+        #
+        # @param [#[]] aliases
+        #   aliases for the columns
+        #
+        # @return [#to_s]
+        #
+        # @api private
+        def column_for(attribute, aliases)
+          if aliases.key?(attribute)
+            alias_for(attribute, aliases[attribute])
+          else
+            dispatch(attribute)
+          end
+        end
+
+        # Return the column alias for an attribute
+        #
+        # @param [#to_s] attribute
+        #
+        # @param [Attribute, nil] alias_attribute
+        #   attribute to use for the alias
+        #
+        # @return [#to_s]
+        #
+        # @api private
+        def alias_for(attribute, alias_attribute)
+          "#{dispatch(attribute)} AS #{dispatch(alias_attribute)}"
+        end
+
+        # Add extensions for extension and summarize queries
+        #
+        # @param [#each] extensions
+        #
+        # @return [undefined]
+        #
+        # @api private
+        def add_extensions(extensions)
+          extensions.each do |attribute, function|
+            @extensions[attribute] = alias_for(function, attribute)
+          end
         end
 
       end # class Relation
     end # module Generator
   end # module SQL