1 files changed, 61 insertions, 0 deletions
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