joins can be created

lib/arel/nodes.rb

@@ -10,3 +10,6 @@
 require 'arel/nodes/update_statement'
 require 'arel/nodes/delete_statement'
 require 'arel/nodes/unqualified_column'
+require 'arel/nodes/table_alias'
+require 'arel/nodes/inner_join'
+require 'arel/nodes/on'

lib/arel/nodes/inner_join.rb

+module Arel
+  module Nodes
+    class InnerJoin
+      attr_accessor :left, :right, :constraint
+
+      def initialize left, right, constraint
+        @left       = left
+        @right      = right
+        @constraint = constraint
+      end
+    end
+  end
+end

lib/arel/nodes/on.rb

+module Arel
+  module Nodes
+    class On
+      attr_accessor :expr
+
+      def initialize expr
+        @expr = expr
+      end
+    end
+  end
+end

lib/arel/nodes/table_alias.rb

+module Arel
+  module Nodes
+    class TableAlias
+      attr_reader :name, :relation, :columns
+
+      def initialize name, relation
+        @name     = name
+        @relation = relation
+        @columns  = relation.columns.map { |column|
+          column.dup.tap { |col| col.relation = self }
+        }
+      end
+
+      def [] name
+        name = name.to_s
+        columns.find { |column| column.name == name }
+      end
+    end
+  end
+end

lib/arel/select_manager.rb

@@ -8,12 +8,21 @@ def initialize engine
       @ctx    = @head.cores.last
     end
 
+    def on expr
+      @ctx.froms.last.constraint = Nodes::On.new(expr)
+      self
+    end
+
     def from table
       @ctx.froms << table
       self
     end
 
     def project projection
+      projection = ::String == projection.class ?
+        Nodes::SqlLiteral.new(projection) :
+        projection
+
       @ctx.projections << projection
       self
     end

lib/arel/table.rb

@@ -5,19 +5,30 @@ class Table
     @engine = nil
     class << self; attr_accessor :engine; end
 
-    attr_reader :name, :engine
+    attr_reader :name, :engine, :aliases
 
     def initialize name, engine = Table.engine
       @name    = name
       @engine  = engine
       @engine  = engine[:engine] if Hash === engine
       @columns = nil
+      @aliases = []
+    end
+
+    def alias
+      Nodes::TableAlias.new("#{name}_2", self).tap do |node|
+        @aliases << node
+      end
     end
 
     def tm
       SelectManager.new(@engine).from(self)
     end
 
+    def join relation
+      SelectManager.new(@engine).from(Nodes::InnerJoin.new(self, relation, nil))
+    end
+
     def where condition
       tm.where condition
     end

lib/arel/visitors/to_sql.rb

@@ -36,7 +36,7 @@ def visit_Arel_Nodes_InsertStatement o
             }.join ', '})" unless o.columns.empty?),
 
           ("VALUES (#{o.values.map { |value|
-            value ? quote(visit(value)) : 'NULL'
+            value ? visit(value) : 'NULL'
           }.join ', '})" unless o.values.empty?),
 
         ].compact.join ' '
@@ -57,12 +57,24 @@ def visit_Arel_Nodes_SelectCore o
         ].compact.join ' '
       end
 
+      def visit_Arel_Nodes_TableAlias o
+        "#{visit o.relation} #{quote_table_name o.name}"
+      end
+
+      def visit_Arel_Nodes_InnerJoin o
+        "#{visit o.left} INNER JOIN #{visit o.right} #{visit o.constraint}"
+      end
+
+      def visit_Arel_Nodes_On o
+        "ON #{visit o.expr}"
+      end
+
       def visit_Arel_Table o
         quote_table_name o.name
       end
 
       def visit_Arel_Nodes_In o
-        "#{visit o.left} IN (#{o.right.map { |x| quote visit x }.join ', '})"
+        "#{visit o.left} IN (#{o.right.map { |x| visit x }.join ', '})"
       end
 
       def visit_Arel_Nodes_Or o
@@ -71,7 +83,7 @@ def visit_Arel_Nodes_Or o
 
       def visit_Arel_Nodes_Equality o
         right = o.right
-        right = right ? quote(visit(right)) : 'NULL'
+        right = right ? visit(right) : 'NULL'
         "#{visit o.left} = #{right}"
       end
 
@@ -87,12 +99,13 @@ def visit_Arel_Attributes_Attribute o
       alias :visit_Arel_Attributes_Time :visit_Arel_Attributes_Attribute
 
       def visit_Fixnum o; o end
-      alias :visit_Time :visit_Fixnum
-      alias :visit_String :visit_Fixnum
-      alias :visit_TrueClass :visit_Fixnum
       alias :visit_Arel_Nodes_SqlLiteral :visit_Fixnum
       alias :visit_Arel_SqlLiteral :visit_Fixnum # This is deprecated
 
+      def visit_TrueClass o; quote(o) end
+      def visit_String o; quote(o) end
+      def visit_Time o; quote(o) end
+
       DISPATCH = {}
       def visit object
         send "visit_#{object.class.name.gsub('::', '_')}", object

spec/arel/select_manager_spec.rb

@@ -54,7 +54,7 @@ def execute sql
         table   = Table.new :users
         manager = Arel::SelectManager.new engine
         manager.from table
-        manager.update('foo = bar')
+        manager.update(SqlLiteral.new('foo = bar'))
 
         engine.executed.last.should be_like %{ UPDATE "users" SET foo = bar }
       end
@@ -89,7 +89,7 @@ def execute sql
       it 'takes strings' do
         table   = Table.new :users
         manager = Arel::SelectManager.new Table.engine
-        manager.project '*'
+        manager.project Nodes::SqlLiteral.new('*')
         manager.to_sql.should be_like %{
           SELECT *
         }
@@ -149,6 +149,24 @@ def execute sql
       end
     end
 
+    describe "join" do
+      it "joins itself" do
+        left      = Table.new :users
+        right     = left.alias
+        predicate = left[:id].eq(right[:id])
+
+        mgr = left.join(right)
+        mgr.project Nodes::SqlLiteral.new('*')
+        check mgr.on(predicate).should == mgr
+
+        mgr.to_sql.should be_like %{
+           SELECT * FROM "users"
+             INNER JOIN "users" "users_2"
+               ON "users"."id" = "users_2"."id"
+        }
+      end
+    end
+
     describe 'from' do
       it "makes sql" do
         table   = Table.new :users

spec/arel/table_spec.rb

@@ -6,6 +6,18 @@ module Arel
       @relation = Table.new(:users)
     end
 
+    describe 'alias' do
+      it 'should create a node that proxies to a table' do
+        check @relation.aliases.should == []
+
+        node = @relation.alias
+        check @relation.aliases.should == [node]
+        check node.name.should == 'users_2'
+        check node[:id].relation.should == node
+        check node[:id].relation.should != node
+      end
+    end
+
     describe 'new' do
       it 'should accept an engine' do
         rel = Table.new :users, 'foo'

spec/arel/update_manager_spec.rb

@@ -21,7 +21,7 @@ module Arel
         table = Table.new(:users)
         um = Arel::UpdateManager.new Table.engine
         um.table table
-        um.set "foo = bar"
+        um.set Nodes::SqlLiteral.new "foo = bar"
         um.to_sql.should be_like %{ UPDATE "users" SET foo = bar }
       end