allow [] on DB, Collection instances to get collections/sub-collections

lib/mongo/collection.rb

@@ -48,6 +48,17 @@ module XGen
           @hint = nil
         end
 
+        # Get a sub-collection of this collection by name.
+        #
+        # Raises InvalidName if an invalid collection name is used.
+        #
+        # :name :: the name of the collection to get
+        def [](name)
+          name = "#{self.name}.#{name}"
+          return Collection.new(self, name) if !db.strict? || db.collection_names.include?(name)
+          raise "Collection #{name} doesn't exist. Currently in strict mode."
+        end
+
         # Set hint fields to use and return +self+. hint may be a single field
         # name, array of field names, or a hash (preferably an OrderedHash).
         # May be +nil+.

lib/mongo/db.rb

@@ -246,6 +246,7 @@ module XGen
           return Collection.new(self, name) if !strict? || collection_names.include?(name)
           raise "Collection #{name} doesn't exist. Currently in strict mode."
         end
+        alias_method :[], :collection
 
         # Drop collection +name+. Returns +true+ on success or if the
         # collection does not exist, +false+ otherwise.

tests/test_collection.rb

@@ -31,6 +31,20 @@ class TestCollection < Test::Unit::TestCase
     @@test.drop()
   end
 
+  def test_collection
+    assert_raise InvalidName do
+      @@db["te$t"]
+    end
+
+    assert_kind_of Collection, @@db["test"]
+    assert_equal @@db["test"].name(), @@db.collection("test").name()
+    assert_equal @@db["test"].name(), @@db[:test].name()
+
+    assert_kind_of Collection, @@db["test"]["foo"]
+    assert_equal @@db["test"]["foo"].name(), @@db.collection("test.foo").name()
+    assert_equal @@db["test"]["foo"].name(), @@db["test.foo"].name()
+  end
+
   def test_safe_insert
     a = {"hello" => "world"}
     @@test.insert(a)