From f0bf1cf7627562c87b6717b6443a56e3060dfda3 Mon Sep 17 00:00:00 2001
From: Aaron Patterson <aaron.patterson@gmail.com>
Date: Tue, 28 Sep 2010 16:57:33 -0700
Subject: refactoring join_sql to return nil if there are no sources

---
 lib/arel/select_manager.rb  |  2 ++
 lib/arel/table.rb           | 21 ++++++++++-----------
 spec/select_manager_spec.rb |  5 +++++
 spec/table_spec.rb          |  7 +++++++
 4 files changed, 24 insertions(+), 11 deletions(-)

diff --git a/lib/arel/select_manager.rb b/lib/arel/select_manager.rb
index 77930a6bb1..adbf1316d7 100644
--- a/lib/arel/select_manager.rb
+++ b/lib/arel/select_manager.rb
@@ -128,6 +128,8 @@ module Arel
     end
 
     def join_sql
+      return nil unless @ctx.froms
+
       viz = Visitors::JoinSql.new @engine
       Nodes::SqlLiteral.new viz.accept @ctx
     end
diff --git a/lib/arel/table.rb b/lib/arel/table.rb
index e71d7d392c..171d165bc2 100644
--- a/lib/arel/table.rb
+++ b/lib/arel/table.rb
@@ -49,40 +49,39 @@ module Arel
     end
 
     def join relation, klass = Nodes::InnerJoin
-      return select_manager unless relation
+      return from(self) unless relation
 
-      sm = SelectManager.new(@engine)
       case relation
       when String, Nodes::SqlLiteral
         raise if relation.blank?
-        sm.from Nodes::StringJoin.new(self, relation)
+        from Nodes::StringJoin.new(self, relation)
       else
-        sm.from klass.new(self, relation, nil)
+        from klass.new(self, relation, nil)
       end
     end
 
     def group *columns
-      select_manager.group(*columns)
+      from(self).group(*columns)
     end
 
     def order *expr
-      select_manager.order(*expr)
+      from(self).order(*expr)
     end
 
     def where condition
-      select_manager.where condition
+      from(self).where condition
     end
 
     def project *things
-      select_manager.project(*things)
+      from(self).project(*things)
     end
 
     def take amount
-      select_manager.take amount
+      from(self).take amount
     end
 
     def having expr
-      select_manager.having expr
+      from(self).having expr
     end
 
     def columns
@@ -98,7 +97,7 @@ module Arel
     end
 
     def select_manager
-      SelectManager.new(@engine, self)
+      SelectManager.new(@engine)
     end
 
     private
diff --git a/spec/select_manager_spec.rb b/spec/select_manager_spec.rb
index e5b65b4698..287657d0c1 100644
--- a/spec/select_manager_spec.rb
+++ b/spec/select_manager_spec.rb
@@ -299,6 +299,11 @@ module Arel
         manager.join_sql.should be_like %{ 'hello' }
         check manager.joins(manager).should == manager.join_sql
       end
+
+      it 'returns nil join sql' do
+        manager = Arel::SelectManager.new Table.engine
+        manager.join_sql.should be_nil
+      end
     end
 
     describe 'order_clauses' do
diff --git a/spec/table_spec.rb b/spec/table_spec.rb
index 15f2e024e0..d0ba46ae56 100644
--- a/spec/table_spec.rb
+++ b/spec/table_spec.rb
@@ -12,6 +12,13 @@ module Arel
       end
     end
 
+    describe 'select_manager' do
+      it 'should return an empty select manager' do
+        sm = @relation.select_manager
+        sm.to_sql.should be_like 'SELECT'
+      end
+    end
+
     describe 'having' do
       it 'adds a having clause' do
         mgr = @relation.having @relation[:id].eq(10)
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