From 7b122f9a336c8c780dcc5a29074f17f3ec493dc6 Mon Sep 17 00:00:00 2001
From: Aaron Patterson <aaron.patterson@gmail.com>
Date: Wed, 8 Sep 2010 15:08:00 -0700
Subject: [PATCH] adding maximum nodes

---
 lib/arel/attributes/attribute.rb       |  4 ++++
 lib/arel/nodes.rb                      |  1 +
 lib/arel/nodes/max.rb                  | 22 ++++++++++++++++++++++
 lib/arel/visitors/to_sql.rb            |  5 +++++
 spec/arel/attributes/attribute_spec.rb | 17 +++++++++++++++++
 spec/arel/nodes/sum_spec.rb            | 12 ++++++++++++
 6 files changed, 61 insertions(+)
 create mode 100644 lib/arel/nodes/max.rb
 create mode 100644 spec/arel/nodes/sum_spec.rb

diff --git a/lib/arel/attributes/attribute.rb b/lib/arel/attributes/attribute.rb
index af9bbdd478..bb85af4634 100644
--- a/lib/arel/attributes/attribute.rb
+++ b/lib/arel/attributes/attribute.rb
@@ -16,6 +16,10 @@ def count distinct = false
       def sum
         Nodes::Sum.new [self], Nodes::SqlLiteral.new('sum_id')
       end
+
+      def maximum
+        Nodes::Max.new [self], Nodes::SqlLiteral.new('max_id')
+      end
     end
 
     class String  < Attribute; end
diff --git a/lib/arel/nodes.rb b/lib/arel/nodes.rb
index 24a71c54a2..28b9e61fb6 100644
--- a/lib/arel/nodes.rb
+++ b/lib/arel/nodes.rb
@@ -6,6 +6,7 @@
 require 'arel/nodes/in'
 require 'arel/nodes/count'
 require 'arel/nodes/sum'
+require 'arel/nodes/max'
 require 'arel/nodes/sql_literal'
 require 'arel/nodes/select_core'
 require 'arel/nodes/select_statement'
diff --git a/lib/arel/nodes/max.rb b/lib/arel/nodes/max.rb
new file mode 100644
index 0000000000..1766c56058
--- /dev/null
+++ b/lib/arel/nodes/max.rb
@@ -0,0 +1,22 @@
+module Arel
+  module Nodes
+    class Max
+      attr_accessor :expressions, :alias
+
+      def initialize expr, aliaz = nil
+        @expressions = expr
+        @alias       = aliaz
+      end
+
+      def as aliaz
+        self.alias = SqlLiteral.new(aliaz)
+        self
+      end
+
+      def to_sql
+        viz = Visitors::ToSql.new Table.engine
+        viz.accept self
+      end
+    end
+  end
+end
diff --git a/lib/arel/visitors/to_sql.rb b/lib/arel/visitors/to_sql.rb
index 2a96444d59..e1cf0f3778 100644
--- a/lib/arel/visitors/to_sql.rb
+++ b/lib/arel/visitors/to_sql.rb
@@ -76,6 +76,11 @@ def visit_Arel_Nodes_Sum o
           visit x }.join(', ')})#{o.alias ? " AS #{visit o.alias}" : ''}"
       end
 
+      def visit_Arel_Nodes_Max o
+        "MAX(#{o.expressions.map { |x|
+          visit x }.join(', ')})#{o.alias ? " AS #{visit o.alias}" : ''}"
+      end
+
       def visit_Arel_Nodes_TableAlias o
         "#{visit o.relation} #{quote_table_name o.name}"
       end
diff --git a/spec/arel/attributes/attribute_spec.rb b/spec/arel/attributes/attribute_spec.rb
index 018f23ea9f..449cc38dad 100644
--- a/spec/arel/attributes/attribute_spec.rb
+++ b/spec/arel/attributes/attribute_spec.rb
@@ -3,6 +3,23 @@
 module Arel
   module Attributes
     describe 'attribute' do
+      describe '#maximum' do
+        it 'should create a MAX node' do
+          relation = Table.new(:users)
+          relation[:id].maximum.should be_kind_of Nodes::Max
+        end
+
+        # FIXME: backwards compat. Is this really necessary?
+        it 'should set the alias to "max_id"' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id].maximum
+          mgr.to_sql.should be_like %{
+            SELECT MAX("users"."id") AS max_id
+            FROM "users"
+          }
+        end
+      end
+
       describe '#sum' do
         it 'should create a SUM node' do
           relation = Table.new(:users)
diff --git a/spec/arel/nodes/sum_spec.rb b/spec/arel/nodes/sum_spec.rb
new file mode 100644
index 0000000000..7691b06590
--- /dev/null
+++ b/spec/arel/nodes/sum_spec.rb
@@ -0,0 +1,12 @@
+require 'spec_helper'
+
+describe Arel::Nodes::Sum do
+  describe "as" do
+    it 'should alias the sum' do
+      table = Arel::Table.new :users
+      table[:id].sum.as('foo').to_sql.should be_like %{
+        SUM("users"."id") AS foo
+      }
+    end
+  end
+end
-- 
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