Add bulk upsert method.

bulk.go

@@ -137,6 +137,30 @@ func (b *Bulk) UpdateAll(pairs ...interface{}) {
 	}
 }
 
+// Upsert queues up the provided pairs of upserting instructions.
+// The first element of each pair selects which documents must be
+// updated, and the second element defines how to update it.
+// Each pair matches exactly one document for updating at most.
+func (b *Bulk) Upsert(pairs ...interface{}) {
+	if len(pairs)%2 != 0 {
+		panic("Bulk.Update requires an even number of parameters")
+	}
+	action := b.action(bulkUpdate)
+	for i := 0; i < len(pairs); i += 2 {
+		selector := pairs[i]
+		if selector == nil {
+			selector = bson.D{}
+		}
+		action.docs = append(action.docs, &updateOp{
+			Collection: b.c.FullName,
+			Selector: selector,
+			Update: pairs[i+1],
+			Flags: 1,
+			Upsert: true,
+		})
+	}
+}
+
 // Run runs all the operations queued up.
 func (b *Bulk) Run() (*BulkResult, error) {
 	var result BulkResult

bulk_test.go

@@ -260,3 +260,26 @@ func (s *S) TestBulkMixedUnordered(c *C) {
 	c.Assert(res, DeepEquals, []doc{{2}, {3}, {4}})
 }
 
+func (s *S) TestBulkUpsert(c *C) {
+	session, err := mgo.Dial("localhost:40001")
+	c.Assert(err, IsNil)
+	defer session.Close()
+
+	coll := session.DB("mydb").C("mycoll")
+
+	err = coll.Insert(M{"n": 1}, M{"n": 2}, M{"n": 3})
+	c.Assert(err, IsNil)
+
+	bulk := coll.Bulk()
+	bulk.Upsert(M{"n": 2}, M{"$set": M{"n": 20}})
+	bulk.Upsert(M{"n": 4}, M{"$set": M{"n": 40}}, M{"n": 3}, M{"$set": M{"n": 30}})
+	r, err := bulk.Run()
+	c.Assert(err, IsNil)
+	c.Assert(r, FitsTypeOf, &mgo.BulkResult{})
+
+	type doc struct{ N int }
+	var res []doc
+	err = coll.Find(nil).Sort("n").All(&res)
+	c.Assert(err, IsNil)
+	c.Assert(res, DeepEquals, []doc{{1}, {20}, {30}, {40}})
+}