full sql statement generation

lib/arel.rb

 require 'arel/version'
 require 'arel/table'
 require 'arel/attributes'
+require 'arel/tree_manager'
 require 'arel/nodes'
 require 'arel/visitors/to_sql'
 

lib/arel/nodes.rb

 require 'arel/nodes/equality'
 require 'arel/nodes/sql_literal'
+require 'arel/nodes/select'

lib/arel/nodes/select.rb

+module Arel
+  module Nodes
+    class Select
+      attr_reader :froms, :projections, :wheres
+
+      def initialize
+        @froms       = []
+        @projections = []
+        @wheres      = []
+      end
+    end
+  end
+end

lib/arel/tree_manager.rb

+module Arel
+  class TreeManager
+    def initialize engine
+      @engine         = engine
+      @statement_list = []
+
+      # default to Select
+      @statement_list << Nodes::Select.new
+    end
+
+    def from table
+      @statement_list.last.froms << table
+      self
+    end
+
+    def project projection
+      @statement_list.last.projections << projection
+      self
+    end
+
+    def where expr
+      @statement_list.last.wheres << expr
+      self
+    end
+
+    def to_sql
+      viz = Visitors::ToSql.new @engine
+      viz.accept @statement_list.last
+    end
+  end
+end

lib/arel/visitors/to_sql.rb

@@ -12,6 +12,18 @@ def accept object
       end
 
       private
+      def visit_Arel_Nodes_Select o
+        [
+          "SELECT #{o.projections.map { |x| visit x }.join ', '}",
+          "FROM #{o.froms.map { |x| visit x }.join ', ' }",
+          ("WHERE #{o.wheres.map { |x| visit x }.join ' AND ' }" unless o.wheres.blank?)
+        ].compact.join ' '
+      end
+
+      def visit_Arel_Table o
+        quote_table_name o.name
+      end
+
       def visit_Arel_Nodes_Equality o
         "#{visit o.left} = #{visit o.right}"
       end

spec/arel/tree_manager.rb

+require 'spec_helper'
+
+module Arel
+  describe 'tree manager' do
+    describe 'where' do
+      it "knows where" do
+        table   = Table.new :users
+        manager = Arel::TreeManager.new Table.engine
+        manager.from(table).project(table['id'])
+        manager.where(table['id'].eq(1))
+        manager.to_sql.should == %{
+          SELECT "users"."id"
+          FROM "users"
+          WHERE "users"."id" = 1
+        }.gsub("\n", '').gsub(/(^\s*|\s*$)/, '').squeeze(' ')
+      end
+
+      it "chains" do
+        table   = Table.new :users
+        manager = Arel::TreeManager.new Table.engine
+        manager.from(table)
+        manager.project(table['id']).where(table['id'].eq 1).should == manager
+      end
+    end
+
+    describe 'from' do
+      it "makes sql" do
+        table   = Table.new :users
+        manager = Arel::TreeManager.new Table.engine
+
+        manager.from table
+        manager.project table['id']
+        manager.to_sql.should == 'SELECT "users"."id" FROM "users"'
+      end
+
+      it "chains" do
+        table   = Table.new :users
+        manager = Arel::TreeManager.new Table.engine
+        manager.from(table).project(table['id']).should == manager
+        manager.to_sql.should == 'SELECT "users"."id" FROM "users"'
+      end
+    end
+  end
+end