8 files changed, 185 insertions, 0 deletions
diff --git a/lib/arel/engines/memory/engine.rb b/lib/arel/engines/memory/engine.rb
new file mode 100644
index 0000000000..c7ac9422d4
--- /dev/null
+++ b/lib/arel/engines/memory/engine.rb
@@ -0,0 +1,16 @@
+module Arel
+  module Memory
+    class Engine
+      module CRUD
+        def read(relation)
+          relation.eval
+        end
+
+        def create(relation)
+          relation.eval
+        end
+      end
+      include CRUD
+    end
+  end
+end
diff --git a/lib/arel/engines/memory/predicates.rb b/lib/arel/engines/memory/predicates.rb
new file mode 100644
index 0000000000..03d4f25b0a
--- /dev/null
+++ b/lib/arel/engines/memory/predicates.rb
@@ -0,0 +1,35 @@
+module Arel
+  class Binary < Predicate
+    def eval(row)
+      operand1.eval(row).send(operator, operand2.eval(row))
+    end
+  end
+
+  class Equality < Binary
+    def operator; :== end
+  end
+
+  class GreaterThanOrEqualTo < Binary
+    def operator; :>= end
+  end
+
+  class GreaterThan < Binary
+    def operator; :> end
+  end
+
+  class LessThanOrEqualTo < Binary
+    def operator; :<= end
+  end
+
+  class LessThan < Binary
+    def operator; :< end
+  end
+
+  class Match < Binary
+    def operator; :=~ end
+  end
+
+  class In < Binary
+    def operator; :include? end
+  end
+end
diff --git a/lib/arel/engines/memory/primitives.rb b/lib/arel/engines/memory/primitives.rb
new file mode 100644
index 0000000000..935b34f5ee
--- /dev/null
+++ b/lib/arel/engines/memory/primitives.rb
@@ -0,0 +1,27 @@
+module Arel
+  class Attribute
+    def eval(row)
+      row[self]
+    end
+  end
+
+  class Value
+    def eval(row)
+      value
+    end
+  end
+
+  class Ordering
+    def eval(row1, row2)
+      (attribute.eval(row1) <=> attribute.eval(row2)) * direction
+    end
+  end
+
+  class Descending < Ordering
+    def direction; -1 end
+  end
+
+  class Ascending < Ordering
+    def direction; 1 end
+  end
+end
diff --git a/lib/arel/engines/memory/relations.rb b/lib/arel/engines/memory/relations.rb
new file mode 100644
index 0000000000..c67af2d63b
--- /dev/null
+++ b/lib/arel/engines/memory/relations.rb
@@ -0,0 +1,5 @@
+require 'arel/engines/memory/relations/array'
+require 'arel/engines/memory/relations/operations'
+require 'arel/engines/memory/relations/writes'
+require 'arel/engines/memory/relations/compound'
+
diff --git a/lib/arel/engines/memory/relations/array.rb b/lib/arel/engines/memory/relations/array.rb
new file mode 100644
index 0000000000..5e7c0a4ab1
--- /dev/null
+++ b/lib/arel/engines/memory/relations/array.rb
@@ -0,0 +1,25 @@
+module Arel
+  class Array < Relation
+    attributes :array,  :attribute_names
+    include Recursion::BaseCase
+    deriving :==, :initialize
+
+    def engine
+      @engine ||= Memory::Engine.new
+    end
+
+    def attributes
+      @attributes ||= @attribute_names.collect do |name|
+        name.to_attribute(self)
+      end
+    end
+
+    def format(attribute, value)
+      value
+    end
+
+    def eval
+      @array.collect { |r| Row.new(self, r) }
+    end
+  end
+end
diff --git a/lib/arel/engines/memory/relations/compound.rb b/lib/arel/engines/memory/relations/compound.rb
new file mode 100644
index 0000000000..6dda92a6a1
--- /dev/null
+++ b/lib/arel/engines/memory/relations/compound.rb
@@ -0,0 +1,9 @@
+module Arel
+  class Compound < Relation
+    delegate :array, :to => :relation
+
+    def unoperated_rows
+      relation.call.collect { |row| row.bind(self) }
+    end
+  end
+end
diff --git a/lib/arel/engines/memory/relations/operations.rb b/lib/arel/engines/memory/relations/operations.rb
new file mode 100644
index 0000000000..8e01938360
--- /dev/null
+++ b/lib/arel/engines/memory/relations/operations.rb
@@ -0,0 +1,61 @@
+module Arel
+  class Where < Compound
+    def eval
+      unoperated_rows.select { |row| predicate.eval(row) }
+    end
+  end
+
+  class Order < Compound
+    def eval
+      unoperated_rows.sort do |row1, row2|
+        ordering = orderings.detect { |o| o.eval(row1, row2) != 0 } || orderings.last
+        ordering.eval(row1, row2)
+      end
+    end
+  end
+
+  class Project < Compound
+    def eval
+      unoperated_rows.collect { |r| r.slice(*projections) }
+    end
+  end
+
+  class Take < Compound
+    def eval
+      unoperated_rows[0, taken]
+    end
+  end
+
+  class Skip < Compound
+    def eval
+      unoperated_rows[skipped..-1]
+    end
+  end
+
+  class Group < Compound
+    def eval
+      raise NotImplementedError
+    end
+  end
+
+  class Alias < Compound
+    def eval
+      unoperated_rows
+    end
+  end
+
+  class Join < Relation
+    def eval
+      result = []
+      relation1.call.each do |row1|
+        relation2.call.each do |row2|
+          combined_row = row1.combine(row2, self)
+          if predicates.all? { |p| p.eval(combined_row) }
+            result << combined_row
+          end
+        end
+      end
+      result
+    end
+  end
+end
diff --git a/lib/arel/engines/memory/relations/writes.rb b/lib/arel/engines/memory/relations/writes.rb
new file mode 100644
index 0000000000..12c4f36c0d
--- /dev/null
+++ b/lib/arel/engines/memory/relations/writes.rb
@@ -0,0 +1,7 @@
+module Arel
+  class Insert < Compound
+    def eval
+      unoperated_rows + [Row.new(self, record.values.collect(&:value))]
+    end
+  end
+end