officially renamed active_relation to arel

21 files changed, 1514 insertions, 0 deletions

diff --git a/spec/arel/unit/predicates/binary_spec.rb b/spec/arel/unit/predicates/binary_spec.rb
new file mode 100644
index 0000000000..f39b37d913
--- /dev/null
+++ b/spec/arel/unit/predicates/binary_spec.rb
@@ -0,0 +1,71 @@
+require File.join(File.dirname(__FILE__), '..', '..', '..', 'spec_helper')
+
+module Arel
+  describe Binary do
+    before do
+      @relation = Table.new(:users)
+      @attribute1 = @relation[:id]
+      @attribute2 = @relation[:name]
+      class ConcreteBinary < Binary
+        def predicate_sql
+          "<=>"
+        end
+      end
+    end
+
+    describe '#to_sql' do
+      describe 'when relating two attributes' do
+        it 'manufactures sql with a binary operation' do
+          ConcreteBinary.new(@attribute1, @attribute2).to_sql.should be_like("
+            `users`.`id` <=> `users`.`name`
+          ")
+        end
+      end
+      
+      describe 'when relating an attribute and a value' do
+        before do
+          @value = "1-asdf"
+        end
+        
+        describe 'when relating to an integer attribute' do
+          it 'formats values as integers' do
+            ConcreteBinary.new(@attribute1, @value).to_sql.should be_like("
+              `users`.`id` <=> 1
+            ")
+          end
+        end
+        
+        describe 'when relating to a string attribute' do
+          it 'formats values as strings' do
+            ConcreteBinary.new(@attribute2, @value).to_sql.should be_like("
+              `users`.`name` <=> '1-asdf'
+            ")
+          end
+        end
+      end
+    end
+    
+    describe '==' do
+      it "obtains if attribute1 and attribute2 are identical" do
+        Binary.new(@attribute1, @attribute2).should == Binary.new(@attribute1, @attribute2)
+        Binary.new(@attribute1, @attribute2).should_not == Binary.new(@attribute1, @attribute1)
+      end
+    
+      it "obtains if the concrete type of the predicates are identical" do
+        Binary.new(@attribute1, @attribute2).should == Binary.new(@attribute1, @attribute2)
+        Binary.new(@attribute1, @attribute2).should_not == ConcreteBinary.new(@attribute1, @attribute2)
+      end
+    end
+  
+    describe '#bind' do
+      before do
+        @another_relation = Table.new(:photos)
+      end
+      
+      it "descends" do
+        ConcreteBinary.new(@attribute1, @attribute2).bind(@another_relation). \
+          should == ConcreteBinary.new(@attribute1.bind(@another_relation), @attribute2.bind(@another_relation))
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/spec/arel/unit/predicates/equality_spec.rb b/spec/arel/unit/predicates/equality_spec.rb
new file mode 100644
index 0000000000..8a58ba3096
--- /dev/null
+++ b/spec/arel/unit/predicates/equality_spec.rb
@@ -0,0 +1,49 @@
+require File.join(File.dirname(__FILE__), '..', '..', '..', 'spec_helper')
+
+module Arel
+  describe Equality do
+    before do
+      @relation1 = Table.new(:users)
+      @relation2 = Table.new(:photos)
+      @attribute1 = @relation1[:id]
+      @attribute2 = @relation2[:user_id]
+    end
+  
+    describe '==' do 
+      it "obtains if attribute1 and attribute2 are identical" do
+        Equality.new(@attribute1, @attribute2).should == Equality.new(@attribute1, @attribute2)
+        Equality.new(@attribute1, @attribute2).should_not == Equality.new(@attribute1, @attribute1)
+      end
+    
+      it "obtains if the concrete type of the predicates are identical" do
+        Equality.new(@attribute1, @attribute2).should_not == Binary.new(@attribute1, @attribute2)
+      end
+    
+      it "is commutative on the attributes" do
+        Equality.new(@attribute1, @attribute2).should == Equality.new(@attribute2, @attribute1)
+      end
+    end
+    
+    describe '#to_sql' do
+      describe 'when relating to a non-nil value' do
+        it "manufactures an equality predicate" do
+          Equality.new(@attribute1, @attribute2).to_sql.should be_like("
+            `users`.`id` = `photos`.`user_id`
+          ")
+        end
+      end
+      
+      describe 'when relation to a nil value' do
+        before do
+          @nil = nil
+        end
+        
+        it "manufactures an is null predicate" do
+          Equality.new(@attribute1, @nil).to_sql.should be_like("
+            `users`.`id` IS NULL
+          ")
+        end
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/spec/arel/unit/predicates/in_spec.rb b/spec/arel/unit/predicates/in_spec.rb
new file mode 100644
index 0000000000..797798a77f
--- /dev/null
+++ b/spec/arel/unit/predicates/in_spec.rb
@@ -0,0 +1,58 @@
+require File.join(File.dirname(__FILE__), '..', '..', '..', 'spec_helper')
+
+module Arel
+  describe In do
+    before do
+      @relation = Table.new(:users)
+      @attribute = @relation[:id]
+    end
+  
+    describe '#to_sql' do 
+      describe 'when relating to an array' do
+        describe 'when the array\'s elements are the same type as the attribute' do
+          before do
+            @array = [1, 2, 3]
+          end
+          
+          it 'manufactures sql with a comma separated list' do
+            In.new(@attribute, @array).to_sql.should be_like("
+              `users`.`id` IN (1, 2, 3)
+            ")        
+          end
+        end
+        
+        describe 'when the array\'s elements are not same type as the attribute' do
+          before do
+            @array = ['1-asdf', 2, 3]
+          end
+          
+          it 'formats values in the array as the type of the attribute' do
+            In.new(@attribute, @array).to_sql.should be_like("
+              `users`.`id` IN (1, 2, 3)
+            ")
+          end
+        end
+      end
+      
+      describe 'when relating to a range' do
+        before do
+          @range = 1..2
+        end
+        
+        it 'manufactures sql with a between' do
+          In.new(@attribute, @range).to_sql.should be_like("
+            `users`.`id` BETWEEN 1 AND 2
+          ")                  
+        end
+      end
+      
+      describe 'when relating to a relation' do
+        it 'manufactures sql with a subselect' do
+          In.new(@attribute, @relation).to_sql.should be_like("
+            `users`.`id` IN (SELECT `users`.`id`, `users`.`name` FROM `users`)
+          ")        
+        end
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/spec/arel/unit/primitives/attribute_spec.rb b/spec/arel/unit/primitives/attribute_spec.rb
new file mode 100644
index 0000000000..ac9afa85c7
--- /dev/null
+++ b/spec/arel/unit/primitives/attribute_spec.rb
@@ -0,0 +1,177 @@
+require File.join(File.dirname(__FILE__), '..', '..', '..', 'spec_helper')
+
+module Arel
+  describe Attribute do
+    before do
+      @relation = Table.new(:users)
+      @attribute = Attribute.new(@relation, :id)
+    end
+  
+    describe Attribute::Transformations do
+      describe '#as' do
+        it "manufactures an aliased attributed" do
+          @attribute.as(:alias).should == Attribute.new(@relation, @attribute.name, :alias => :alias, :ancestor => @attribute)
+        end
+      end
+    
+      describe '#bind' do
+        it "manufactures an attribute with the relation bound and self as an ancestor" do
+          derived_relation = @relation.select(@relation[:id].eq(1))
+          @attribute.bind(derived_relation).should == Attribute.new(derived_relation, @attribute.name, :ancestor => @attribute)
+        end
+        
+        it "returns self if the substituting to the same relation" do
+          @attribute.bind(@relation).should == @attribute
+        end
+      end
+    
+      describe '#to_attribute' do
+        it "returns self" do
+          @attribute.to_attribute.should == @attribute
+        end
+      end
+    end
+    
+    describe '#column' do
+      it "returns the corresponding column in the relation" do
+        @attribute.column.should == @relation.column_for(@attribute)
+      end
+    end
+    
+    describe '#qualified_name' do
+      it "manufactures an attribute name prefixed with the relation's name" do
+        @attribute.qualified_name.should == "#{@relation.prefix_for(@attribute)}.id"
+      end
+    end
+    
+    describe '#engine' do
+      it "delegates to its relation" do
+        Attribute.new(@relation, :id).engine.should == @relation.engine
+      end
+    end
+    
+    describe Attribute::Congruence do
+      describe '=~' do
+        
+        it "obtains if the attributes are identical" do
+          Attribute.new(@relation, :name).should =~ Attribute.new(@relation, :name)
+        end
+      
+        it "obtains if the attributes have an overlapping history" do
+          Attribute.new(@relation, :name, :ancestor => Attribute.new(@relation, :name)).should =~ Attribute.new(@relation, :name)
+          Attribute.new(@relation, :name).should =~ Attribute.new(@relation, :name, :ancestor => Attribute.new(@relation, :name))
+        end
+      end
+      
+      describe 'hashing' do
+        it "implements hash equality" do
+          Attribute.new(@relation, 'name').should hash_the_same_as(Attribute.new(@relation, 'name'))
+          Attribute.new(@relation, 'name').should_not hash_the_same_as(Attribute.new(@relation, 'id'))
+        end
+      end
+    end
+    
+    describe '#to_sql' do
+      describe 'for a simple attribute' do
+        it "manufactures sql with an alias" do
+          @attribute.to_sql.should be_like("`users`.`id`")
+        end
+      end
+      
+      describe 'for an attribute in a join relation where the source relation is aliased' do
+        before do
+          another_relation = Table.new(:photos)
+          @join_with_alias = @relation.as(:alias).join(another_relation).on(@relation[:id].eq(another_relation[:user_id]))
+        end
+        
+        it "manufactures sql with an alias" do
+          @join_with_alias[@attribute].to_sql.should be_like("`alias`.`id`")
+        end
+      end
+    end
+  
+    describe Attribute::Predications do
+      before do
+        @attribute = Attribute.new(@relation, :name)
+      end
+    
+      describe '#eq' do
+        it "manufactures an equality predicate" do
+          @attribute.eq('name').should == Equality.new(@attribute, 'name')
+        end
+      end
+    
+      describe '#lt' do
+        it "manufactures a less-than predicate" do
+          @attribute.lt(10).should == LessThan.new(@attribute, 10)
+        end
+      end
+    
+      describe '#lteq' do
+        it "manufactures a less-than or equal-to predicate" do
+          @attribute.lteq(10).should == LessThanOrEqualTo.new(@attribute, 10)
+        end
+      end
+    
+      describe '#gt' do
+        it "manufactures a greater-than predicate" do
+          @attribute.gt(10).should == GreaterThan.new(@attribute, 10)
+        end
+      end
+    
+      describe '#gteq' do
+        it "manufactures a greater-than or equal-to predicate" do
+          @attribute.gteq(10).should == GreaterThanOrEqualTo.new(@attribute, 10)
+        end
+      end
+    
+      describe '#matches' do
+        it "manufactures a match predicate" do
+          @attribute.matches(/.*/).should == Match.new(@attribute, /.*/)
+        end
+      end
+      
+      describe '#in' do
+        it "manufactures an in predicate" do
+          @attribute.in(1..30).should == In.new(@attribute, (1..30))
+        end
+      end
+    end
+  
+    describe Attribute::Expressions do
+      before do
+        @attribute = Attribute.new(@relation, :name)    
+      end
+    
+      describe '#count' do
+        it "manufactures a count Expression" do
+          @attribute.count.should == Expression.new(@attribute, "COUNT")
+        end
+      end
+    
+      describe '#sum' do
+        it "manufactures a sum Expression" do
+          @attribute.sum.should == Expression.new(@attribute, "SUM")
+        end
+      end
+    
+      describe '#maximum' do
+        it "manufactures a maximum Expression" do
+          @attribute.maximum.should == Expression.new(@attribute, "MAX")
+        end
+      end
+    
+      describe '#minimum' do
+        it "manufactures a minimum Expression" do
+          @attribute.minimum.should == Expression.new(@attribute, "MIN")
+        end
+      end
+    
+      describe '#average' do
+        it "manufactures an average Expression" do
+          @attribute.average.should == Expression.new(@attribute, "AVG")
+        end
+      end 
+    end
+  end
+end
\ No newline at end of file
diff --git a/spec/arel/unit/primitives/expression_spec.rb b/spec/arel/unit/primitives/expression_spec.rb
new file mode 100644
index 0000000000..8a990231f6
--- /dev/null
+++ b/spec/arel/unit/primitives/expression_spec.rb
@@ -0,0 +1,45 @@
+require File.join(File.dirname(__FILE__), '..', '..', '..', 'spec_helper')
+
+module Arel
+  describe Expression do
+    before do
+      @relation = Table.new(:users)
+      @attribute = @relation[:id]
+    end
+    
+    describe Expression::Transformations do
+      before do
+        @expression = Expression.new(@attribute, "COUNT")
+      end
+      
+      describe '#bind' do
+        it "manufactures an attribute with a rebound relation and self as the ancestor" do
+          derived_relation = @relation.select(@relation[:id].eq(1))
+          @expression.bind(derived_relation).should == Expression.new(@attribute.bind(derived_relation), "COUNT", nil, @expression)
+        end
+        
+        it "returns self if the substituting to the same relation" do
+          @expression.bind(@relation).should == @expression
+        end
+      end
+      
+      describe '#as' do
+        it "manufactures an aliased expression" do
+          @expression.as(:alias).should == Expression.new(@attribute, "COUNT", :alias, @expression)
+        end
+      end
+      
+      describe '#to_attribute' do
+        it "manufactures an attribute with the expression as an ancestor" do
+          @expression.to_attribute.should == Attribute.new(@expression.relation, @expression.alias, :ancestor => @expression)
+        end
+      end
+    end
+    
+    describe '#to_sql' do
+      it "manufactures sql with the expression and alias" do
+        Expression.new(@attribute, "COUNT", :alias).to_sql.should == "COUNT(`users`.`id`) AS `alias`"
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/spec/arel/unit/primitives/value_spec.rb b/spec/arel/unit/primitives/value_spec.rb
new file mode 100644
index 0000000000..87425c780d
--- /dev/null
+++ b/spec/arel/unit/primitives/value_spec.rb
@@ -0,0 +1,28 @@
+require File.join(File.dirname(__FILE__), '..', '..', '..', 'spec_helper')
+
+module Arel
+  describe Value do
+    before do
+      @relation = Table.new(:users)
+    end
+    
+    describe '#to_sql' do
+      it "appropriately quotes the value" do
+        Value.new(1, @relation).to_sql.should be_like('1')
+        Value.new('asdf', @relation).to_sql.should be_like("'asdf'")
+      end
+    end
+
+    describe '#format' do
+      it "returns the sql of the provided object" do
+        Value.new(1, @relation).format(@relation[:id]).should == @relation[:id].to_sql
+      end
+    end
+
+    describe '#bind' do
+      it "manufactures a new value whose relation is the provided relation" do
+        Value.new(1, @relation).bind(another_relation = Table.new(:photos)).should == Value.new(1, another_relation)
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/spec/arel/unit/relations/alias_spec.rb b/spec/arel/unit/relations/alias_spec.rb
new file mode 100644
index 0000000000..420a91c806
--- /dev/null
+++ b/spec/arel/unit/relations/alias_spec.rb
@@ -0,0 +1,16 @@
+require File.join(File.dirname(__FILE__), '..', '..', '..', 'spec_helper')
+
+module Arel
+  describe Alias do
+    before do
+      @relation = Table.new(:users)
+      @alias_relation = Alias.new(@relation, :foo)
+    end
+    
+    describe '#alias' do
+      it "returns the alias" do
+        @alias_relation.alias.should == :foo
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/spec/arel/unit/relations/compound_spec.rb b/spec/arel/unit/relations/compound_spec.rb
new file mode 100644
index 0000000000..763e447db3
--- /dev/null
+++ b/spec/arel/unit/relations/compound_spec.rb
@@ -0,0 +1,31 @@
+require File.join(File.dirname(__FILE__), '..', '..', '..', 'spec_helper')
+
+module Arel
+  describe Compound do
+    before do
+      class ConcreteCompound < Compound
+        def initialize(relation)
+          @relation = relation
+        end
+        
+        def ==(other)
+          true
+        end
+      end
+      @relation = Table.new(:users)
+      @compound_relation = ConcreteCompound.new(@relation)
+    end
+    
+    describe '#attributes' do
+      it 'manufactures attributes associated with the compound relation' do
+        @compound_relation.attributes.should == @relation.attributes.collect { |a| a.bind(@compound_relation) }
+      end
+    end
+    
+    describe 'hashing' do
+      it 'implements hash equality' do
+        ConcreteCompound.new(@relation).should hash_the_same_as(ConcreteCompound.new(@relation))
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/spec/arel/unit/relations/deletion_spec.rb b/spec/arel/unit/relations/deletion_spec.rb
new file mode 100644
index 0000000000..f975720d83
--- /dev/null
+++ b/spec/arel/unit/relations/deletion_spec.rb
@@ -0,0 +1,42 @@
+require File.join(File.dirname(__FILE__), '..', '..', '..', 'spec_helper')
+
+module Arel
+  describe Deletion do
+    before do
+      @relation = Table.new(:users)
+    end
+  
+    describe '#to_sql' do
+      it 'manufactures sql deleting a table relation' do
+        Deletion.new(@relation).to_sql.should be_like("
+          DELETE
+          FROM `users`
+        ")
+      end
+    
+      it 'manufactures sql deleting a selection relation' do
+        Deletion.new(@relation.select(@relation[:id].eq(1))).to_sql.should be_like("
+          DELETE
+          FROM `users`
+          WHERE `users`.`id` = 1
+        ")
+      end
+      
+      it "manufactures sql deleting a ranged relation" do
+        Deletion.new(@relation.take(1)).to_sql.should be_like("
+          DELETE
+          FROM `users`
+          LIMIT 1
+        ")
+      end
+    end
+    
+    describe '#call' do
+      it 'executes a delete on the connection' do
+        deletion = Deletion.new(@relation)
+        mock(connection = Object.new).delete(deletion.to_sql)
+        deletion.call(connection)
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/spec/arel/unit/relations/grouping_spec.rb b/spec/arel/unit/relations/grouping_spec.rb
new file mode 100644
index 0000000000..bef3566896
--- /dev/null
+++ b/spec/arel/unit/relations/grouping_spec.rb
@@ -0,0 +1,33 @@
+require File.join(File.dirname(__FILE__), '..', '..', '..', 'spec_helper')
+
+module Arel
+  describe Grouping do
+    before do
+      @relation = Table.new(:users)
+      @attribute = @relation[:id]
+    end
+  
+    describe '#to_sql' do
+      describe 'when given a predicate' do
+        it "manufactures sql with where clause conditions" do
+          Grouping.new(@relation, @attribute).to_sql.should be_like("
+            SELECT `users`.`id`, `users`.`name`
+            FROM `users`
+            GROUP BY `users`.`id`
+          ")
+        end
+      end
+      
+      describe 'when given a string' do
+        it "passes the string through to the where clause" do
+          pending 'it should not quote asdf'
+          Grouping.new(@relation, 'asdf').to_sql.should be_like("
+            SELECT `users`.`id`, `users`.`name`
+            FROM `users`
+            GROUP BY asdf
+          ")
+        end
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/spec/arel/unit/relations/insertion_spec.rb b/spec/arel/unit/relations/insertion_spec.rb
new file mode 100644
index 0000000000..10b70a2036
--- /dev/null
+++ b/spec/arel/unit/relations/insertion_spec.rb
@@ -0,0 +1,71 @@
+require File.join(File.dirname(__FILE__), '..', '..', '..', 'spec_helper')
+
+module Arel
+  describe Insertion do
+    before do
+      @relation = Table.new(:users)
+    end
+  
+    describe '#to_sql' do
+      it 'manufactures sql inserting data when given multiple rows' do
+        pending 'it should insert multiple rows'
+        @insertion = Insertion.new(@relation, [@relation[:name] => "nick", @relation[:name] => "bryan"])
+      
+        @insertion.to_sql.should be_like("
+          INSERT
+          INTO `users`
+          (`users`.`name`) VALUES ('nick'), ('bryan')
+        ")
+      end
+      
+      it 'manufactures sql inserting data when given multiple values' do
+        @insertion = Insertion.new(@relation, @relation[:id] => "1", @relation[:name] => "nick")
+      
+        @insertion.to_sql.should be_like("
+          INSERT
+          INTO `users`
+          (`users`.`id`, `users`.`name`) VALUES (1, 'nick')
+        ")
+      end
+      
+      describe 'when given values whose types correspond to the types of the attributes' do
+        before do
+          @insertion = Insertion.new(@relation, @relation[:name] => "nick")
+        end
+        
+        it 'manufactures sql inserting data' do
+          @insertion.to_sql.should be_like("
+            INSERT
+            INTO `users`
+            (`users`.`name`) VALUES ('nick')
+          ")
+        end
+      end
+      
+      describe 'when given values whose types differ from from the types of the attributes' do
+        before do
+          @insertion = Insertion.new(@relation, @relation[:id] => '1-asdf')
+        end
+        
+        it 'manufactures sql inserting data' do
+          @insertion.to_sql.should be_like("
+            INSERT
+            INTO `users`
+            (`users`.`id`) VALUES (1)
+          ")
+        end
+      end
+    end
+    
+    describe '#call' do
+      before do
+        @insertion = Insertion.new(@relation, @relation[:name] => "nick")
+      end
+      
+      it 'executes an insert on the connection' do
+        mock(connection = Object.new).insert(@insertion.to_sql)
+        @insertion.call(connection)
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/spec/arel/unit/relations/join_spec.rb b/spec/arel/unit/relations/join_spec.rb
new file mode 100644
index 0000000000..f9d0d9561e
--- /dev/null
+++ b/spec/arel/unit/relations/join_spec.rb
@@ -0,0 +1,169 @@
+require File.join(File.dirname(__FILE__), '..', '..', '..', 'spec_helper')
+
+module Arel
+  describe Join do
+    before do
+      @relation1 = Table.new(:users)
+      @relation2 = Table.new(:photos)
+      @predicate = @relation1[:id].eq(@relation2[:user_id])
+    end
+
+    describe '==' do
+      before do
+        @another_predicate = @relation1[:id].eq(1)
+        @another_relation = Table.new(:cameras)
+      end
+      
+      it 'obtains if the two relations and the predicate are identical' do
+        Join.new("INNER JOIN", @relation1, @relation2, @predicate).should == Join.new("INNER JOIN", @relation1, @relation2, @predicate)
+        Join.new("INNER JOIN", @relation1, @relation2, @predicate).should_not == Join.new("INNER JOIN", @relation1, @another_relation, @predicate)
+        Join.new("INNER JOIN", @relation1, @relation2, @predicate).should_not == Join.new("INNER JOIN", @relation1, @relation2, @another_predicate)
+      end
+  
+      it 'is commutative on the relations' do
+        Join.new("INNER JOIN", @relation1, @relation2, @predicate).should == Join.new("INNER JOIN", @relation2, @relation1, @predicate)
+      end
+    end
+    
+    describe 'hashing' do
+      it 'implements hash equality' do
+        Join.new("INNER JOIN", @relation1, @relation2, @predicate) \
+          .should hash_the_same_as(Join.new("INNER JOIN", @relation1, @relation2, @predicate))
+      end
+    end
+
+    describe '#prefix_for' do
+      describe 'when the joined relations are simple' do
+        it "returns the name of the relation containing the attribute" do
+          Join.new("INNER JOIN", @relation1, @relation2, @predicate).prefix_for(@relation1[:id]) \
+            .should == @relation1.prefix_for(@relation1[:id])
+          Join.new("INNER JOIN", @relation1, @relation2, @predicate).prefix_for(@relation2[:id]) \
+            .should == @relation2.prefix_for(@relation2[:id])
+          
+        end
+      end
+      
+      describe 'when one of the joined relations is an alias' do
+        before do
+          @aliased_relation = @relation1.as(:alias)
+        end
+        
+        it "returns the alias of the relation containing the attribute" do
+          Join.new("INNER JOIN", @aliased_relation, @relation2, @predicate).prefix_for(@aliased_relation[:id]) \
+            .should == @aliased_relation.alias
+          Join.new("INNER JOIN", @aliased_relation, @relation2, @predicate).prefix_for(@relation2[:id]) \
+            .should == @relation2.prefix_for(@relation2[:id])
+        end
+      end
+    end
+    
+    describe '#engine' do
+      it "delegates to a relation's engine" do
+        Join.new("INNER JOIN", @relation1, @relation2, @predicate).engine.should == @relation1.engine
+      end
+    end
+    
+    describe 'when joining simple relations' do
+      describe '#attributes' do
+        it 'combines the attributes of the two relations' do
+          join = Join.new("INNER JOIN", @relation1, @relation2, @predicate)
+          join.attributes.should ==
+            (@relation1.attributes + @relation2.attributes).collect { |a| a.bind(join) }
+        end
+      end
+      
+      describe '#to_sql' do
+        it 'manufactures sql joining the two tables on the predicate' do
+          Join.new("INNER JOIN", @relation1, @relation2, @predicate).to_sql.should be_like("
+            SELECT `users`.`id`, `users`.`name`, `photos`.`id`, `photos`.`user_id`, `photos`.`camera_id`
+            FROM `users`
+              INNER JOIN `photos` ON `users`.`id` = `photos`.`user_id`
+          ")
+        end
+
+        it 'manufactures sql joining the two tables, merging any selects' do
+          Join.new("INNER JOIN", @relation1.select(@relation1[:id].eq(1)),
+                                 @relation2.select(@relation2[:id].eq(2)), @predicate).to_sql.should be_like("
+            SELECT `users`.`id`, `users`.`name`, `photos`.`id`, `photos`.`user_id`, `photos`.`camera_id`
+            FROM `users`
+              INNER JOIN `photos` ON `users`.`id` = `photos`.`user_id`
+            WHERE `users`.`id` = 1
+              AND `photos`.`id` = 2
+          ")          
+        end
+      end
+    end
+    
+    describe 'when joining aggregated relations' do
+      before do
+        @aggregation = @relation2                                           \
+          .group(@relation2[:user_id])                                      \
+          .project(@relation2[:user_id], @relation2[:id].count.as(:cnt))    \
+          .as('photo_count')
+      end
+      
+      describe '#attributes' do
+        it 'it transforms aggregate expressions into attributes' do
+          join_with_aggregation = Join.new("INNER JOIN", @relation1, @aggregation, @predicate)
+          join_with_aggregation.attributes.should ==
+            (@relation1.attributes + @aggregation.attributes).collect(&:to_attribute).collect { |a| a.bind(join_with_aggregation) }
+        end
+      end
+      
+      describe '#to_sql' do
+        describe 'with the aggregation on the right' do
+          it 'manufactures sql joining the left table to a derived table' do
+            Join.new("INNER JOIN", @relation1, @aggregation, @predicate).to_sql.should be_like("
+              SELECT `users`.`id`, `users`.`name`, `photo_count`.`user_id`, `photo_count`.`cnt`
+              FROM `users`
+                INNER JOIN (SELECT `photos`.`user_id`, COUNT(`photos`.`id`) AS `cnt` FROM `photos` GROUP BY `photos`.`user_id`) AS `photo_count`
+                  ON `users`.`id` = `photo_count`.`user_id`
+            ")
+          end
+        end
+
+        describe 'with the aggregation on the left' do
+          it 'manufactures sql joining the right table to a derived table' do
+            Join.new("INNER JOIN", @aggregation, @relation1, @predicate).to_sql.should be_like("
+              SELECT `photo_count`.`user_id`, `photo_count`.`cnt`, `users`.`id`, `users`.`name`
+              FROM (SELECT `photos`.`user_id`, COUNT(`photos`.`id`) AS `cnt` FROM `photos` GROUP BY `photos`.`user_id`) AS `photo_count`
+                INNER JOIN `users`
+                  ON `users`.`id` = `photo_count`.`user_id`
+            ")
+          end
+        end
+
+        it "keeps selects on the aggregation within the derived table" do
+          Join.new("INNER JOIN", @relation1, @aggregation.select(@aggregation[:user_id].eq(1)), @predicate).to_sql.should be_like("
+            SELECT `users`.`id`, `users`.`name`, `photo_count`.`user_id`, `photo_count`.`cnt`
+            FROM `users`
+              INNER JOIN (SELECT `photos`.`user_id`, COUNT(`photos`.`id`) AS `cnt` FROM `photos` WHERE `photos`.`user_id` = 1 GROUP BY `photos`.`user_id`) AS `photo_count`
+                ON `users`.`id` = `photo_count`.`user_id`
+          ")
+        end
+      end
+    end
+    
+    describe 'when joining aliased relations' do
+      it 'aliases the table and attributes properly' do
+        aliased_relation = @relation1.as(:alias)
+        @relation1.join(aliased_relation).on(@relation1[:id].eq(aliased_relation[:id])).to_sql.should be_like("
+          SELECT `users`.`id`, `users`.`name`, `alias`.`id`, `alias`.`name`
+          FROM `users`
+            INNER JOIN `users` AS `alias`
+              ON `users`.`id` = `alias`.`id`
+        ")
+      end
+    end
+    
+    describe 'when joining with a string' do
+      it "passes the string through to the where clause" do
+        Join.new("INNER JOIN asdf ON fdsa", @relation1).to_sql.should be_like("
+          SELECT `users`.`id`, `users`.`name`
+          FROM `users`
+            INNER JOIN asdf ON fdsa
+        ")        
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/spec/arel/unit/relations/order_spec.rb b/spec/arel/unit/relations/order_spec.rb
new file mode 100644
index 0000000000..838a2f141e
--- /dev/null
+++ b/spec/arel/unit/relations/order_spec.rb
@@ -0,0 +1,77 @@
+require File.join(File.dirname(__FILE__), '..', '..', '..', 'spec_helper')
+
+module Arel
+  describe Order do
+    before do
+      @relation = Table.new(:users)
+      @attribute = @relation[:id]
+    end
+
+    describe '#initialize' do
+      before do
+        @another_attribtue = @relation[:name]
+      end
+      
+      it "manufactures nested Order relations if multiple predicates are provided" do
+        Order.new(@relation, @predicate, @another_attribute). \
+          should == Order.new(Order.new(@relation, @another_attribute), @predicate)
+      end
+    end
+    
+    describe '#to_sql' do
+      describe "when given an attribute" do
+        it "manufactures sql with an order clause populated by the attribute" do
+          Order.new(@relation, @attribute).to_sql.should be_like("
+            SELECT `users`.`id`, `users`.`name`
+            FROM `users`
+            ORDER BY `users`.`id`
+          ")
+        end
+      end
+      
+      describe "when given multiple attributes" do
+        before do
+          @another_attribute = @relation[:name]
+        end
+        
+        it "manufactures sql with an order clause populated by comma-separated attributes" do
+          Order.new(@relation, @attribute, @another_attribute).to_sql.should be_like("
+            SELECT `users`.`id`, `users`.`name`
+            FROM `users`
+            ORDER BY `users`.`id`, `users`.`name`
+          ")
+        end
+      end
+      
+      describe "when given a string" do
+        before do
+          @string = "asdf"
+        end
+        
+        it "passes the string through to the order clause" do
+          Order.new(@relation, @string).to_sql.should be_like("
+            SELECT `users`.`id`, `users`.`name`
+            FROM `users`
+            ORDER BY asdf
+          ")
+        end
+      end
+      
+      describe "when ordering an ordered relation" do
+        before do
+          @ordered_relation = Order.new(@relation, @attribute)
+          @another_attribute = @relation[:name]
+        end
+        
+        it "manufactures sql with an order clause populated by comma-separated attributes" do
+          Order.new(@ordered_relation, @another_attribute).to_sql.should be_like("
+            SELECT `users`.`id`, `users`.`name`
+            FROM `users`
+            ORDER BY `users`.`id`, `users`.`name`
+          ")
+        end
+      end
+    end
+  end
+end
+  
\ No newline at end of file
diff --git a/spec/arel/unit/relations/projection_spec.rb b/spec/arel/unit/relations/projection_spec.rb
new file mode 100644
index 0000000000..cd59d6c383
--- /dev/null
+++ b/spec/arel/unit/relations/projection_spec.rb
@@ -0,0 +1,81 @@
+require File.join(File.dirname(__FILE__), '..', '..', '..', 'spec_helper')
+
+module Arel
+  describe Projection do
+    before do
+      @relation = Table.new(:users)
+      @attribute = @relation[:id]
+    end
+    
+    describe '#attributes' do
+      before do
+        @projection = Projection.new(@relation, @attribute)
+      end
+      
+      it "manufactures attributes associated with the projection relation" do
+        @projection.attributes.should == [@attribute].collect { |a| a.bind(@projection) }
+      end
+    end
+    
+    describe '==' do
+      before do
+        @another_relation = Table.new(:photos)
+        @another_attribute = @relation[:name]
+      end
+      
+      it "obtains if the relations and attributes are identical" do
+        Projection.new(@relation, @attribute).should == Projection.new(@relation, @attribute)
+        Projection.new(@relation, @attribute).should_not == Projection.new(@another_relation, @attribute)
+        Projection.new(@relation, @attribute).should_not == Projection.new(@relation, @another_attribute)
+      end
+    end
+  
+    describe '#to_sql' do
+      describe 'when given an attribute' do
+        it "manufactures sql with a limited select clause" do
+          Projection.new(@relation, @attribute).to_sql.should be_like("
+            SELECT `users`.`id`
+            FROM `users`
+          ")
+        end
+      end
+      
+      describe 'when given a relation' do
+        before do
+          @scalar_relation = Projection.new(@relation, @relation[:name])
+        end
+        
+        it "manufactures sql with scalar selects" do
+          Projection.new(@relation, @scalar_relation).to_sql.should be_like("
+            SELECT (SELECT `users`.`name` FROM `users`) FROM `users`
+          ")
+        end
+      end
+      
+      describe 'when given a string' do
+        it "passes the string through to the select clause" do
+          Projection.new(@relation, 'asdf').to_sql.should be_like("
+            SELECT asdf FROM `users`
+          ")
+        end
+      end
+    end
+    
+    describe Projection::Externalizable do
+      describe '#aggregation?' do
+        describe 'when the projections are attributes' do
+          it 'returns false' do
+            Projection.new(@relation, @attribute).should_not be_aggregation
+          end
+        end
+        
+        describe 'when the projections include an aggregation' do
+          it "obtains" do
+            Projection.new(@relation, @attribute.sum).should be_aggregation
+          end
+        end
+      end
+
+    end
+  end
+end
\ No newline at end of file
diff --git a/spec/arel/unit/relations/relation_spec.rb b/spec/arel/unit/relations/relation_spec.rb
new file mode 100644
index 0000000000..46c3ee250d
--- /dev/null
+++ b/spec/arel/unit/relations/relation_spec.rb
@@ -0,0 +1,215 @@
+require File.join(File.dirname(__FILE__), '..', '..', '..', 'spec_helper')
+
+module Arel
+  describe Relation do
+    before do
+      @relation = Table.new(:users)
+      @attribute1 = @relation[:id]
+      @attribute2 = @relation[:name]
+    end
+  
+    describe '[]' do
+      describe 'when given an', Attribute do
+        it "return the attribute congruent to the provided attribute" do
+          @relation[@attribute1].should == @attribute1
+        end
+      end
+      
+      describe 'when given a', Symbol, String do
+        it "returns the attribute with the same name, if it exists" do
+          @relation[:id].should == @attribute1
+          @relation['id'].should == @attribute1
+          @relation[:does_not_exist].should be_nil
+        end
+      end
+    end
+  
+    describe Relation::Externalizable do
+      describe '#aggregation?' do
+        it "returns false" do
+          @relation.should_not be_aggregation
+        end
+      end
+
+      describe '#alias?' do
+        it "returns false" do
+          @relation.should_not be_alias
+        end
+      end
+    end
+    
+    describe Relation::Operations do
+      describe 'joins' do
+        before do
+          @predicate = @relation[:id].eq(@relation[:id])
+        end
+      
+        describe '#join' do
+          describe 'when given a relation' do
+            it "manufactures an inner join operation between those two relations" do
+              @relation.join(@relation).on(@predicate). \
+                should == Join.new("INNER JOIN", @relation, @relation, @predicate)
+            end
+          end
+          
+          describe "when given a string" do
+            it "manufactures a join operation with the string passed through" do
+              @relation.join(arbitrary_string = "ASDF").should == Join.new(arbitrary_string, @relation) 
+            end
+          end
+          
+          describe "when given something blank" do
+            it "returns self" do
+              @relation.join.should == @relation
+            end
+          end
+        end
+
+        describe '#outer_join' do
+          it "manufactures a left outer join operation between those two relations" do
+            @relation.outer_join(@relation).on(@predicate). \
+              should == Join.new("LEFT OUTER JOIN", @relation, @relation, @predicate)
+          end
+        end
+      end
+
+      describe '#project' do
+        it "manufactures a projection relation" do
+          @relation.project(@attribute1, @attribute2). \
+            should == Projection.new(@relation, @attribute1, @attribute2)
+        end
+        
+        describe "when given blank attributes" do
+          it "returns self" do
+            @relation.project.should == @relation
+          end
+        end
+      end
+
+      describe '#as' do
+        it "manufactures an alias relation" do
+          @relation.as(:paul).should == Alias.new(@relation, :paul)
+        end
+        
+        describe 'when given a blank alias' do
+          it 'returns self' do
+            @relation.as.should == @relation
+          end
+        end
+      end
+  
+      describe '#select' do
+        before do
+          @predicate = Equality.new(@attribute1, @attribute2)
+        end
+    
+        it "manufactures a selection relation" do
+          @relation.select(@predicate).should == Selection.new(@relation, @predicate)
+        end
+    
+        it "accepts arbitrary strings" do
+          @relation.select("arbitrary").should == Selection.new(@relation, "arbitrary")
+        end
+        
+        describe 'when given a blank predicate' do
+          it 'returns self' do
+            @relation.select.should == @relation
+          end
+        end
+      end
+  
+      describe '#order' do
+        it "manufactures an order relation" do
+          @relation.order(@attribute1, @attribute2).should == Order.new(@relation, @attribute1, @attribute2)
+        end
+        
+        describe 'when given a blank ordering' do
+          it 'returns self' do
+            @relation.order.should == @relation
+          end
+        end
+      end
+      
+      describe '#take' do
+        it "manufactures a take relation" do
+          @relation.take(5).should == Take.new(@relation, 5)
+        end
+        
+        describe 'when given a blank number of items' do
+          it 'returns self' do
+            @relation.take.should == @relation
+          end
+        end
+      end
+      
+      describe '#skip' do
+        it "manufactures a skip relation" do
+          @relation.skip(4).should == Skip.new(@relation, 4)
+        end
+        
+        describe 'when given a blank number of items' do
+          it 'returns self' do
+            @relation.skip.should == @relation
+          end
+        end
+      end
+
+      describe '#group' do
+        it 'manufactures a group relation' do
+          @relation.group(@attribute1, @attribute2).should == Grouping.new(@relation, @attribute1, @attribute2)
+        end
+        
+        describe 'when given blank groupings' do
+          it 'returns self' do
+            @relation.group.should == @relation
+          end
+        end
+      end
+      
+      describe Relation::Operations::Writes do
+        describe '#delete' do
+          it 'manufactures a deletion relation' do
+            Session.start do
+              mock(Session.new).delete(Deletion.new(@relation))
+              @relation.delete.should == @relation
+            end
+          end
+        end
+
+        describe '#insert' do
+          it 'manufactures an insertion relation' do
+            Session.start do
+              record = {@relation[:name] => 'carl'}
+              mock(Session.new).create(Insertion.new(@relation, record))
+              @relation.insert(record).should == @relation
+            end
+          end
+        end
+
+        describe '#update' do
+          it 'manufactures an update relation' do
+            Session.start do
+              assignments = {@relation[:name] => Value.new('bob', @relation)}
+              mock(Session.new).update(Update.new(@relation, assignments))
+              @relation.update(assignments).should == @relation
+            end
+          end
+        end
+      end
+    end
+      
+    describe Relation::Enumerable do
+      it "implements enumerable" do
+        @relation.collect.should == @relation.session.read(@relation)
+        @relation.first.should == @relation.session.read(@relation).first
+      end
+    end
+    
+    describe '#call' do
+      it 'executes a select_all on the connection' do
+        mock(connection = Object.new).select_all(@relation.to_sql)
+        @relation.call(connection)
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/spec/arel/unit/relations/selection_spec.rb b/spec/arel/unit/relations/selection_spec.rb
new file mode 100644
index 0000000000..61d9787df2
--- /dev/null
+++ b/spec/arel/unit/relations/selection_spec.rb
@@ -0,0 +1,43 @@
+require File.join(File.dirname(__FILE__), '..', '..', '..', 'spec_helper')
+
+module Arel
+  describe Selection do
+    before do
+      @relation = Table.new(:users)
+      @predicate = @relation[:id].eq(1)
+    end
+  
+    describe '#initialize' do
+      before do
+        @another_predicate = @relation[:name].lt(2)
+      end
+      
+      it "manufactures nested selection relations if multiple predicates are provided" do
+        Selection.new(@relation, @predicate, @another_predicate). \
+          should == Selection.new(Selection.new(@relation, @another_predicate), @predicate)
+      end
+    end
+    
+    describe '#to_sql' do
+      describe 'when given a predicate' do
+        it "manufactures sql with where clause conditions" do
+          Selection.new(@relation, @predicate).to_sql.should be_like("
+            SELECT `users`.`id`, `users`.`name`
+            FROM `users`
+            WHERE `users`.`id` = 1
+          ")
+        end
+      end
+      
+      describe 'when given a string' do
+        it "passes the string through to the where clause" do
+          Selection.new(@relation, 'asdf').to_sql.should be_like("
+            SELECT `users`.`id`, `users`.`name`
+            FROM `users`
+            WHERE asdf
+          ")
+        end
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/spec/arel/unit/relations/skip_spec.rb b/spec/arel/unit/relations/skip_spec.rb
new file mode 100644
index 0000000000..d83c969aa8
--- /dev/null
+++ b/spec/arel/unit/relations/skip_spec.rb
@@ -0,0 +1,20 @@
+require File.join(File.dirname(__FILE__), '..', '..', '..', 'spec_helper')
+
+module Arel
+  describe Skip do
+    before do
+      @relation = Table.new(:users)
+      @skipped = 4
+    end
+
+    describe '#to_sql' do
+      it "manufactures sql with limit and offset" do
+        Skip.new(@relation, @skipped).to_s.should be_like("
+          SELECT `users`.`id`, `users`.`name`
+          FROM `users`
+          OFFSET #{@skipped}
+        ")
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/spec/arel/unit/relations/table_spec.rb b/spec/arel/unit/relations/table_spec.rb
new file mode 100644
index 0000000000..eb765ce777
--- /dev/null
+++ b/spec/arel/unit/relations/table_spec.rb
@@ -0,0 +1,95 @@
+require File.join(File.dirname(__FILE__), '..', '..', '..', 'spec_helper')
+
+module Arel
+  describe Table do
+    before do
+      @relation = Table.new(:users)
+    end
+  
+    describe '[]' do
+      describe 'when given a', Symbol do
+        it "manufactures an attribute if the symbol names an attribute within the relation" do
+          @relation[:id].should == Attribute.new(@relation, :id)
+          @relation[:does_not_exist].should be_nil
+        end
+      end
+
+      describe 'when given an', Attribute do
+        it "returns the attribute if the attribute is within the relation" do
+          @relation[@relation[:id]].should == @relation[:id]
+        end
+        
+        it "returns nil if the attribtue is not within the relation" do
+          another_relation = Table.new(:photos)
+          @relation[another_relation[:id]].should be_nil
+        end
+      end
+      
+      describe 'when given an', Expression do
+        before do
+          @expression = @relation[:id].count
+        end
+        
+        it "returns the Expression if the Expression is within the relation" do
+          @relation[@expression].should be_nil
+        end
+      end
+    end
+    
+    describe '#to_sql' do
+      it "manufactures a simple select query" do
+        @relation.to_sql.should be_like("
+          SELECT `users`.`id`, `users`.`name`
+          FROM `users`
+        ")
+      end
+    end
+    
+    describe '#column_for' do
+      it "returns the column corresponding to the attribute" do
+        @relation.column_for(@relation[:id]).should == @relation.columns.detect { |c| c.name == 'id' }
+      end
+    end
+    
+    describe '#prefix_for' do
+      it "returns the table name if the relation contains the attribute" do
+        @relation.prefix_for(@relation[:id]).should == 'users'
+        @relation.prefix_for(:does_not_exist).should be_nil
+      end
+    end
+    
+    describe '#attributes' do
+      it 'manufactures attributes corresponding to columns in the table' do
+        @relation.attributes.should == [
+          Attribute.new(@relation, :id),
+          Attribute.new(@relation, :name)
+        ]
+      end
+      
+      describe '#reset' do
+        it "reloads columns from the database" do
+          lambda { stub(@relation.engine).columns { [] } }.should_not change { @relation.attributes }
+          lambda { @relation.reset }.should change { @relation.attributes }
+        end
+      end
+    end
+  
+    describe 'hashing' do
+      it "implements hash equality" do
+        Table.new(:users).should hash_the_same_as(Table.new(:users))
+        Table.new(:users).should_not hash_the_same_as(Table.new(:photos))
+      end
+    end
+    
+    describe '#engine' do
+      it "defaults to global engine" do
+        Table.engine = engine = Engine.new
+        Table.new(:users).engine.should == engine
+      end
+      
+      it "can be specified" do
+        Table.new(:users, engine = Engine.new).engine.should == engine
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/spec/arel/unit/relations/take_spec.rb b/spec/arel/unit/relations/take_spec.rb
new file mode 100644
index 0000000000..dca7806057
--- /dev/null
+++ b/spec/arel/unit/relations/take_spec.rb
@@ -0,0 +1,20 @@
+require File.join(File.dirname(__FILE__), '..', '..', '..', 'spec_helper')
+
+module Arel
+  describe Take do
+    before do
+      @relation = Table.new(:users)
+      @taken = 4
+    end
+
+    describe '#to_sql' do
+      it "manufactures sql with limit and offset" do
+        Take.new(@relation, @taken).to_s.should be_like("
+          SELECT `users`.`id`, `users`.`name`
+          FROM `users`
+          LIMIT #{@taken}
+        ")
+      end
+    end
+  end
+end
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diff --git a/spec/arel/unit/relations/update_spec.rb b/spec/arel/unit/relations/update_spec.rb
new file mode 100644
index 0000000000..f411781392
--- /dev/null
+++ b/spec/arel/unit/relations/update_spec.rb
@@ -0,0 +1,81 @@
+require File.join(File.dirname(__FILE__), '..', '..', '..', 'spec_helper')
+
+module Arel
+  describe Update do
+    before do
+      @relation = Table.new(:users)
+    end
+    
+    describe '#to_sql' do
+      it "manufactures sql updating attributes when given multiple attributes" do
+        Update.new(@relation, @relation[:id] => 1, @relation[:name] => "nick").to_sql.should be_like("
+          UPDATE `users`
+          SET `users`.`id` = 1, `users`.`name` = 'nick'
+        ")
+      end
+      
+      it "manufactures sql updating attributes when given a ranged relation" do
+        Update.new(@relation.take(1), @relation[:name] => "nick").to_sql.should be_like("
+          UPDATE `users`
+          SET `users`.`name` = 'nick'
+          LIMIT 1
+        ")
+      end
+      
+      describe 'when given values whose types correspond to the types of the attributes' do
+        before do
+          @update = Update.new(@relation, @relation[:name] => "nick")
+        end
+        
+        it 'manufactures sql updating attributes' do
+          @update.to_sql.should be_like("
+            UPDATE `users`
+            SET `users`.`name` = 'nick'
+          ")
+        end
+      end
+
+      describe 'when given values whose types differ from from the types of the attributes' do
+        before do
+          @update = Update.new(@relation, @relation[:id] => '1-asdf')
+        end
+        
+        it 'manufactures sql updating attributes' do
+          @update.to_sql.should be_like("
+            UPDATE `users`
+            SET `users`.`id` = 1
+          ")
+        end
+      end
+            
+      describe 'when the relation is a selection' do
+        before do
+          @update = Update.new(
+            @relation.select(@relation[:id].eq(1)),
+            @relation[:name] => "nick"
+          )
+        end
+        
+        it 'manufactures sql updating a selection relation' do
+          @update.to_sql.should be_like("
+            UPDATE `users`
+            SET `users`.`name` = 'nick'
+            WHERE `users`.`id` = 1
+          ")
+        end
+      end
+    end
+    
+    describe '#call' do
+      before do
+        @update = Update.new(@relation, @relation[:name] => "nick")
+      end
+      
+      it 'executes an update on the connection' do
+        mock(connection = Object.new).update(@update.to_sql)
+        @update.call(connection)
+      end
+    end
+    
+  end
+end
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diff --git a/spec/arel/unit/session/session_spec.rb b/spec/arel/unit/session/session_spec.rb
new file mode 100644
index 0000000000..c2eb9a4555
--- /dev/null
+++ b/spec/arel/unit/session/session_spec.rb
@@ -0,0 +1,92 @@
+require File.join(File.dirname(__FILE__), '..', '..', '..', 'spec_helper')
+
+module Arel
+  describe Session do
+    before do
+      @relation = Table.new(:users)
+      @session = Session.new
+    end
+    
+    describe '::start' do
+      describe '::instance' do
+        it "it is a singleton within the started session" do
+          Session.start do
+            Session.new.should == Session.new
+          end
+        end
+
+        it "is a singleton across nested sessions" do
+          Session.start do
+            outside = Session.new
+            Session.start do
+              Session.new.should == outside
+            end
+          end
+        end
+      
+        it "manufactures new sessions outside of the started session" do
+          Session.new.should_not == Session.new
+        end
+      end
+    end
+    
+    describe Session::CRUD do
+      before do
+        @insert = Insertion.new(@relation, @relation[:name] => 'nick')
+        @update = Update.new(@relation, @relation[:name] => 'nick')
+        @delete = Deletion.new(@relation)
+        @read = @relation
+      end
+      
+      describe '#create' do
+        it "executes an insertion on the connection" do
+          mock(@insert).call(@insert.engine.connection)
+          @session.create(@insert)
+        end
+      end
+      
+      describe '#read' do
+        it "executes an selection on the connection" do
+          mock(@read).call(@read.engine.connection)
+          @session.read(@read)
+        end
+        
+        it "is memoized" do
+          mock(@read).call(@read.engine.connection).once
+          @session.read(@read)
+          @session.read(@read)
+        end
+      end
+      
+      describe '#update' do
+        it "executes an update on the connection" do
+          mock(@update).call(@update.engine.connection)
+          @session.update(@update)
+        end
+      end
+      
+      describe '#delete' do
+        it "executes a delete on the connection" do
+          mock(@delete).call(@delete.engine.connection)
+          @session.delete(@delete)
+        end
+      end
+    end
+    
+    describe Session::Transactions do
+      describe '#begin' do
+      end
+    
+      describe '#end' do
+      end
+    end
+    
+    describe Session::UnitOfWork do
+      describe '#flush' do
+      end
+      
+      describe '#clear' do
+      end
+    end
+  end
+end
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