Mingo.many method for declaring one-to-many

lib/mingo.rb

@@ -14,6 +14,7 @@ class Mingo < Hashie::Dash
   extend ActiveModel::Translation
 
   autoload :Cursor, 'mingo/cursor'
+  autoload :ManyProxy, 'mingo/many_proxy'
 
   class << self
     attr_writer :db, :collection
@@ -56,6 +57,16 @@ def find(selector = {}, options = {}, &block)
     def create(obj = nil)
       new(obj).tap { |doc| doc.save }
     end
+
+    def many(property, model, &block)
+      proxy_class = block_given?? Class.new(ManyProxy, &block) : ManyProxy
+      ivar = "@#{property}"
+
+      define_method(property) {
+        (instance_variable_defined?(ivar) && instance_variable_get(ivar)) ||
+          instance_variable_set(ivar, proxy_class.new(self, property, model))
+      }
+    end
   end
 
   attr_reader :changes

lib/mingo/many_proxy.rb

@@ -0,0 +1,88 @@
+class Mingo
+  class ManyProxy
+    def self.decorate_with(mod = nil, &block)
+      if mod or block_given?
+        @decorate_with = mod || Module.new(&block)
+      else
+        @decorate_with
+      end
+    end
+
+    def self.decorate_each(&block)
+      if block_given?
+        @decorate_each = block
+      else
+        @decorate_each
+      end
+    end
+
+    def initialize(parent, property, model)
+      @parent = parent
+      @property = property
+      @model = model
+      @collection = nil
+      @embedded = (@parent[@property] ||= [])
+      @parent.changes.delete(@property)
+    end
+
+    def find_options
+      @find_options ||= begin
+        decorator = self.class.decorate_with
+        decorate_block = self.class.decorate_each
+
+        if decorator or decorate_block
+          {:convert => lambda { |doc|
+            @model.new(doc).tap do |obj|
+              obj.extend decorator if decorator
+              decorate_block.call(obj, @embedded) if decorate_block
+            end
+          }}
+        else
+          {}
+        end
+      end
+    end
+
+    undef :to_a, :inspect
+
+    def object_ids
+      @embedded
+    end
+
+    def convert(doc)
+      doc.id
+    end
+
+    def <<(doc)
+      doc = convert(doc)
+      @parent.update '$addToSet' => { @property => doc }
+      unload_collection
+      @embedded << doc
+      self
+    end
+
+    def delete(doc)
+      doc = convert(doc)
+      @parent.update '$pull' => { @property => doc }
+      unload_collection
+      @embedded.delete doc
+    end
+
+    private
+
+    def method_missing(method, *args, &block)
+      load_collection
+      @collection.send(method, *args, &block)
+    end
+
+    def unload_collection
+      @collection = nil
+    end
+
+    def load_collection
+      @collection ||= if @embedded.empty? then []
+      else @model.find({:_id => {'$in' => self.object_ids}}, find_options)
+      end
+    end
+  end
+end