Moving aggregation into Criteria API

lib/mongoid/criteria.rb

@@ -14,8 +14,23 @@ module Mongoid #:nodoc:
   #
   # <tt>criteria.execute</tt>
   class Criteria
+    attr_accessor :klass
     attr_reader :selector, :options, :type
 
+    AGGREGATE_REDUCE = "function(obj, prev) { prev.count++; }"
+    # Aggregate the criteria. This will take the internally built selector and options
+    # and pass them on to the Ruby driver's +group()+ method on the collection. The
+    # collection itself will be retrieved from the class provided, and once the
+    # query has returned it will provided a grouping of keys with counts.
+    #
+    # Example:
+    # 
+    # <tt>criteria.select(:field1).where(:field1 => "Title").aggregate(Person)</tt>
+    def aggregate(klass = nil)
+      @klass = klass if klass
+      @klass.collection.group(@options[:fields], @selector, { :count => 0 }, AGGREGATE_REDUCE)
+    end
+
     # Adds a criterion to the +Criteria+ that specifies values that must all
     # be matched in order to return results. Similar to an "in" clause but the
     # underlying conditional logic is an "AND" and not an "OR". The MongoDB
@@ -67,9 +82,10 @@ def excludes(exclusions = {})
     #
     # If this is a +Criteria+ to find multiple results, will return an +Array+ of
     # objects of the type of class provided.
-    def execute(klass)
-      return klass.new(klass.collection.find_one(@selector, @options)) if type == :first
-      return klass.collection.find(@selector, @options).collect { |doc| klass.new(doc) }
+    def execute(klass = nil)
+      @klass = klass if klass
+      return @klass.new(klass.collection.find_one(@selector, @options)) if type == :first
+      return @klass.collection.find(@selector, @options).collect { |doc| klass.new(doc) }
     end
 
     # Adds a criterion to the +Criteria+ that specifies additional options
@@ -129,8 +145,9 @@ def id(object_id)
     # Options:
     #
     # type: One of :all, :first:, or :last
-    def initialize(type)
-      @selector, @options, @type = {}, {}, type
+    # klass: The class to execute on.
+    def initialize(type, klass = nil)
+      @selector, @options, @type, @klass = {}, {}, type, klass
     end
 
     # Adds a criterion to the +Criteria+ that specifies the maximum number of

lib/mongoid/document.rb

@@ -4,7 +4,6 @@ class Document
     include Commands, Observable, Validatable
     extend Associations
 
-    AGGREGATE_REDUCE = "function(obj, prev) { prev.count++; }"
     GROUP_BY_REDUCE = "function(obj, prev) { prev.group.push(obj); }"
 
     attr_accessor :parent
@@ -20,13 +19,6 @@ class Document
 
     class << self
 
-      # Get an aggregate count for the supplied group of fields and the
-      # selector that is provided.
-      def aggregate(fields, params = {})
-        selector = params[:conditions]
-        collection.group(fields, selector, { :count => 0 }, AGGREGATE_REDUCE)
-      end
-
       # Returns the collection associated with this +Document+. If the
       # document is embedded, there will be no collection associated
       # with it.
@@ -159,7 +151,7 @@ def paginate(params = {})
       #
       # Returns: <tt>Criteria</tt>
       def select(*args)
-        Criteria.new(:all).select(*args)
+        Criteria.new(:all, self).select(*args)
       end
 
     end

spec/unit/mongoid/criteria_spec.rb

@@ -6,6 +6,41 @@
     @criteria = Mongoid::Criteria.new(:all)
   end
 
+  describe "#aggregate" do
+
+    context "when klass provided" do
+
+      before do
+        @reduce = "function(obj, prev) { prev.count++; }"
+        @criteria = Mongoid::Criteria.new(:all, Person)
+        @collection = mock
+        Person.expects(:collection).returns(@collection)
+      end
+
+      it "calls group on the collection with the aggregate js" do
+        @collection.expects(:group).with([:field1], {}, {:count => 0}, @reduce)
+        @criteria.select(:field1).aggregate
+      end
+
+    end
+
+    context "when klass not provided" do
+
+      before do
+        @reduce = "function(obj, prev) { prev.count++; }"
+        @collection = mock
+        Person.expects(:collection).returns(@collection)
+      end
+
+      it "calls group on the collection with the aggregate js" do
+        @collection.expects(:group).with([:field1], {}, {:count => 0}, @reduce)
+        @criteria.select(:field1).aggregate(Person)
+      end
+
+    end
+
+  end
+
   describe "#all" do
 
     it "adds the $all query to the selector" do

spec/unit/mongoid/document_spec.rb

@@ -14,21 +14,6 @@
     @collection = nil
   end
 
-  describe "#aggregate" do
-
-    before do
-      @reduce = "function(obj, prev) { prev.count++; }"
-    end
-
-    it "returns documents grouped by the supplied fields" do
-      results = [{ "title" => "Sir", "count" => 30 }]
-      @collection.expects(:group).with([:title], nil, {:count => 0}, @reduce).returns(results)
-      grouped = Person.aggregate([:title], {})
-      grouped.first["count"].should == 30
-    end
-
-  end
-
   describe "#all" do
 
     before do