Add equality to ALL THE THINGS (that matter)

People are often trying to use ARel nodes inside ActiveRecord, and when
they do so, lots of things can break, because ActiveRecord relies on
Array#uniq and sometimes hash key equality to handle values that end up
in wheres, havings, etc. By implementing equality for all the nodes, we
should hopefully be able to prevent any nodes (even nodes containing
other nodes) from failing an equality check they should otherwise pass,
and alleviate many of these errors.

Fixes #130

lib/arel/nodes/and.rb

@@ -18,6 +18,16 @@ def left
       def right
         children[1]
       end
+
+      def hash
+        children.hash
+      end
+
+      def eql? other
+        self.class == other.class &&
+          self.children == other.children
+      end
+      alias :== :eql?
     end
   end
 end

lib/arel/nodes/binary.rb

@@ -13,6 +13,17 @@ def initialize_copy other
         @left  = @left.clone if @left
         @right = @right.clone if @right
       end
+
+      def hash
+        [@left, @right].hash
+      end
+
+      def eql? other
+        self.class == other.class &&
+          self.left == other.left &&
+          self.right == other.right
+      end
+      alias :== :eql?
     end
 
     %w{

lib/arel/nodes/extract.rb

@@ -18,6 +18,17 @@ def as aliaz
         self.alias = SqlLiteral.new(aliaz)
         self
       end
+
+      def hash
+        super ^ [@field, @alias].hash
+      end
+
+      def eql? other
+        super &&
+          self.field == other.field &&
+          self.alias == other.alias
+      end
+      alias :== :eql?
     end
   end
 end

lib/arel/nodes/false.rb

@@ -1,6 +1,13 @@
 module Arel
   module Nodes
     class False < Arel::Nodes::Node
+      def hash
+        self.class.hash
+      end
+
+      def eql? other
+        self.class == other.class
+      end
     end
   end
 end

lib/arel/nodes/function.rb

@@ -16,6 +16,17 @@ def as aliaz
         self.alias = SqlLiteral.new(aliaz)
         self
       end
+
+      def hash
+        [@expressions, @alias, @distinct].hash
+      end
+
+      def eql? other
+        self.class == other.class &&
+          self.expressions == other.expressions &&
+          self.alias == other.alias &&
+          self.distinct == other.distinct
+      end
     end
 
     %w{

lib/arel/nodes/insert_statement.rb

@@ -14,6 +14,18 @@ def initialize_copy other
         @columns = @columns.clone
         @values =  @values.clone if @values
       end
+
+      def hash
+        [@relation, @columns, @values].hash
+      end
+
+      def eql? other
+        self.class == other.class &&
+          self.relation == other.relation &&
+          self.columns == other.columns &&
+          self.values == other.values
+      end
+      alias :== :eql?
     end
   end
 end

lib/arel/nodes/named_function.rb

@@ -7,6 +7,15 @@ def initialize name, expr, aliaz = nil
         super(expr, aliaz)
         @name = name
       end
+
+      def hash
+        super ^ @name.hash
+      end
+
+      def eql? other
+        super && self.name == other.name
+      end
+      alias :== :eql?
     end
   end
 end

lib/arel/nodes/select_core.rb

@@ -37,6 +37,26 @@ def initialize_copy other
         @having      = @having.clone if @having
         @windows     = @windows.clone
       end
+
+      def hash
+        [
+          @source, @top, @set_quantifier, @projections,
+          @wheres, @groups, @having, @windows
+        ].hash
+      end
+
+      def eql? other
+        self.class == other.class &&
+          self.source == other.source &&
+          self.top == other.top &&
+          self.set_quantifier == other.set_quantifier &&
+          self.projections == other.projections &&
+          self.wheres == other.wheres &&
+          self.groups == other.groups &&
+          self.having == other.having &&
+          self.windows == other.windows
+      end
+      alias :== :eql?
     end
   end
 end

lib/arel/nodes/select_statement.rb

@@ -5,7 +5,6 @@ class SelectStatement < Arel::Nodes::Node
       attr_accessor :limit, :orders, :lock, :offset, :with
 
       def initialize cores = [SelectCore.new]
-        #puts caller
         @cores          = cores
         @orders         = []
         @limit          = nil
@@ -19,6 +18,21 @@ def initialize_copy other
         @cores  = @cores.map { |x| x.clone }
         @orders = @orders.map { |x| x.clone }
       end
+
+      def hash
+        [@cores, @orders, @limit, @lock, @offset, @with].hash
+      end
+
+      def eql? other
+        self.class == other.class &&
+          self.cores == other.cores &&
+          self.orders == other.orders &&
+          self.limit == other.limit &&
+          self.lock == other.lock &&
+          self.offset == other.offset &&
+          self.with == other.with
+      end
+      alias :== :eql?
     end
   end
 end

lib/arel/nodes/terminal.rb

@@ -1,6 +1,13 @@
 module Arel
   module Nodes
     class Distinct < Arel::Nodes::Node
+      def hash
+        self.class.hash
+      end
+
+      def eql? other
+        self.class == other.class
+      end
     end
   end
 end

lib/arel/nodes/true.rb

@@ -1,6 +1,13 @@
 module Arel
   module Nodes
     class True < Arel::Nodes::Node
+      def hash
+        self.class.hash
+      end
+
+      def eql? other
+        self.class == other.class
+      end
     end
   end
 end

lib/arel/nodes/unary.rb

@@ -7,6 +7,16 @@ class Unary < Arel::Nodes::Node
       def initialize expr
         @expr = expr
       end
+
+      def hash
+        @expr.hash
+      end
+
+      def eql? other
+        self.class == other.class &&
+          self.expr == other.expr
+      end
+      alias :== :eql?
     end
 
     %w{

lib/arel/nodes/update_statement.rb

@@ -18,6 +18,21 @@ def initialize_copy other
         @wheres = @wheres.clone
         @values = @values.clone
       end
+
+      def hash
+        [@relation, @wheres, @values, @orders, @limit, @key].hash
+      end
+
+      def eql? other
+        self.class == other.class &&
+          self.relation == other.relation &&
+          self.wheres == other.wheres &&
+          self.values == other.values &&
+          self.orders == other.orders &&
+          self.limit == other.limit &&
+          self.key == other.key
+      end
+      alias :== :eql?
     end
   end
 end

lib/arel/nodes/window.rb

@@ -32,6 +32,17 @@ def initialize_copy other
         super
         @orders = @orders.map { |x| x.clone }
       end
+
+      def hash
+        [@orders, @framing].hash
+      end
+
+      def eql? other
+        self.class == other.class &&
+          self.orders == other.orders &&
+          self.framing == other.framing
+      end
+      alias :== :eql?
     end
 
     class NamedWindow < Window
@@ -46,6 +57,15 @@ def initialize_copy other
         super
         @name = other.name.clone
       end
+
+      def hash
+        super ^ @name.hash
+      end
+
+      def eql? other
+        super && self.name == other.name
+      end
+      alias :== :eql?
     end
 
     class Rows < Unary
@@ -60,7 +80,15 @@ def initialize(expr = nil)
       end
     end
 
-    class CurrentRow < Arel::Nodes::Node; end
+    class CurrentRow < Node
+      def hash
+        self.class.hash
+      end
+
+      def eql? other
+        self.class == other.class
+      end
+    end
 
     class Preceding < Unary
       def initialize(expr = nil)

lib/arel/table.rb

@@ -123,6 +123,19 @@ def insert_manager
       InsertManager.new(@engine)
     end
 
+    def hash
+      [@name, @engine, @aliases, @table_alias].hash
+    end
+
+    def eql? other
+      self.class == other.class &&
+        self.name == other.name &&
+        self.engine == other.engine &&
+        self.aliases == other.aliases &&
+        self.table_alias == other.table_alias
+    end
+    alias :== :eql?
+
     private
 
     def attributes_for columns

test/nodes/test_and.rb

@@ -0,0 +1,20 @@
+require 'helper'
+
+module Arel
+  module Nodes
+    describe 'And' do
+      describe 'equality' do
+        it 'is equal with equal ivars' do
+          array = [And.new(['foo', 'bar']), And.new(['foo', 'bar'])]
+          assert_equal 1, array.uniq.size
+        end
+
+        it 'is not equal with different ivars' do
+          array = [And.new(['foo', 'bar']), And.new(['foo', 'baz'])]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+  end
+end
+

test/nodes/test_as.rb

@@ -17,6 +17,18 @@ module Nodes
           assert_kind_of Arel::Nodes::SqlLiteral, as.right
         end
       end
+
+      describe 'equality' do
+        it 'is equal with equal ivars' do
+          array = [As.new('foo', 'bar'), As.new('foo', 'bar')]
+          assert_equal 1, array.uniq.size
+        end
+
+        it 'is not equal with different ivars' do
+          array = [As.new('foo', 'bar'), As.new('foo', 'baz')]
+          assert_equal 2, array.uniq.size
+        end
+      end
     end
   end
 end

test/nodes/test_ascending.rb

@@ -29,6 +29,16 @@ def test_descending?
         ascending = Ascending.new 'zomg'
         assert !ascending.descending?
       end
+
+      def test_equality_with_same_ivars
+        array = [Ascending.new('zomg'), Ascending.new('zomg')]
+        assert_equal 1, array.uniq.size
+      end
+
+      def test_inequality_with_different_ivars
+        array = [Ascending.new('zomg'), Ascending.new('zomg!')]
+        assert_equal 2, array.uniq.size
+      end
     end
   end
 end

test/nodes/test_bin.rb

@@ -18,6 +18,16 @@ def test_mysql_to_sql
         node = Arel::Nodes::Bin.new(Arel.sql('zomg'))
         assert_equal 'BINARY zomg', viz.accept(node)
       end
+
+      def test_equality_with_same_ivars
+        array = [Bin.new('zomg'), Bin.new('zomg')]
+        assert_equal 1, array.uniq.size
+      end
+
+      def test_inequality_with_different_ivars
+        array = [Bin.new('zomg'), Bin.new('zomg!')]
+        assert_equal 2, array.uniq.size
+      end
     end
   end
 end