8 files changed, 116 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..67a084f2cd
--- /dev/null
+++ b/lib/arel/engines/memory/engine.rb
@@ -0,0 +1,12 @@
+module Arel
+  module Memory
+    class Engine
+      module CRUD
+        def read(relation)
+          relation.eval
+        end
+      end
+      include CRUD
+    end
+  end
+end
+\ No newline at end of file
diff --git a/lib/arel/engines/memory/predicates.rb b/lib/arel/engines/memory/predicates.rb
new file mode 100644
index 0000000000..3522ea3ffa
--- /dev/null
+++ b/lib/arel/engines/memory/predicates.rb
@@ -0,0 +1,58 @@
+module Arel
+  class Predicate
+    def or(other_predicate)
+      Or.new(self, other_predicate)
+    end
+
+    def and(other_predicate)
+      And.new(self, other_predicate)
+    end
+  end
+
+  class Binary < Predicate
+    def eval(row)
+      operand1.eval(row).send(operator, operand2.eval(row))
+    end
+  end
+
+  class CompoundPredicate < Binary
+    def to_sql(formatter = nil)
+      "(#{operand1.to_sql(formatter)} #{predicate_sql} #{operand2.to_sql(formatter)})"
+    end
+  end
+
+  class Or < CompoundPredicate
+    def predicate_sql; "OR" end
+  end
+
+  class And < CompoundPredicate
+    def predicate_sql; "AND" end
+  end
+
+  class Equality < Binary
+    def ==(other)
+      Equality === other and
+        ((operand1 == other.operand1 and operand2 == other.operand2) or
+         (operand1 == other.operand2 and operand2 == other.operand1))
+    end
+  end
+
+  class GreaterThanOrEqualTo < Binary
+  end
+
+  class GreaterThan < Binary
+  end
+
+  class LessThanOrEqualTo < Binary
+  end
+
+  class LessThan < Binary
+    def operator; :< end
+  end
+
+  class Match < Binary
+  end
+
+  class In < Binary
+  end
+end
diff --git a/lib/arel/engines/memory/primitives.rb b/lib/arel/engines/memory/primitives.rb
new file mode 100644
index 0000000000..4d5c76e956
--- /dev/null
+++ b/lib/arel/engines/memory/primitives.rb
@@ -0,0 +1,2 @@
+require 'arel/engines/memory/primitives/attribute'
+require 'arel/engines/memory/primitives/value'
diff --git a/lib/arel/engines/memory/primitives/attribute.rb b/lib/arel/engines/memory/primitives/attribute.rb
new file mode 100644
index 0000000000..9864feadc2
--- /dev/null
+++ b/lib/arel/engines/memory/primitives/attribute.rb
@@ -0,0 +1,7 @@
+module Arel
+  class Attribute
+    def eval(row)
+      row[self]
+    end
+  end
+end
+\ No newline at end of file
diff --git a/lib/arel/engines/memory/primitives/value.rb b/lib/arel/engines/memory/primitives/value.rb
new file mode 100644
index 0000000000..b83cd02e57
--- /dev/null
+++ b/lib/arel/engines/memory/primitives/value.rb
@@ -0,0 +1,7 @@
+module Arel
+  class Value
+    def eval(row)
+      value
+    end
+  end
+end
+\ No newline at end of file
diff --git a/lib/arel/engines/memory/relations.rb b/lib/arel/engines/memory/relations.rb
new file mode 100644
index 0000000000..6361d7c9d7
--- /dev/null
+++ b/lib/arel/engines/memory/relations.rb
@@ -0,0 +1,2 @@
+require 'arel/engines/memory/relations/array'
+require 'arel/engines/memory/relations/operations/where'
diff --git a/lib/arel/engines/memory/relations/array.rb b/lib/arel/engines/memory/relations/array.rb
new file mode 100644
index 0000000000..c02c62891b
--- /dev/null
+++ b/lib/arel/engines/memory/relations/array.rb
@@ -0,0 +1,21 @@
+module Arel
+  class Array < Relation
+    attributes :array,  :attribute_names
+    deriving :initialize
+    include Recursion::BaseCase
+    
+    def engine
+      @engine ||= Memory::Engine.new
+    end
+
+    def attributes
+      @attributes ||= @attribute_names.collect do |name|
+        Attribute.new(self, name.to_sym)
+      end
+    end
+
+    def eval
+      @array.collect { |row| attributes.zip(row).to_hash }
+    end
+  end
+end
+\ No newline at end of file
diff --git a/lib/arel/engines/memory/relations/operations/where.rb b/lib/arel/engines/memory/relations/operations/where.rb
new file mode 100644
index 0000000000..eb11fb55fd
--- /dev/null
+++ b/lib/arel/engines/memory/relations/operations/where.rb
@@ -0,0 +1,7 @@
+module Arel
+  class Where < Compound
+    def eval
+      relation.eval.select { |row| predicate.eval(row) }
+    end
+  end
+end
+\ No newline at end of file