在Mongoid中是否有内置的方法来进行upsert(如果不存在则插入)？或者我应该先检查一个项目是否存在,并且只有在那之后才能进行插入/更新？
解决方法
Mongoid中已经有一个内置的upsert方法
Model#upsert Performs a MongoDB upsert on the document. If the
document exists in the database,it will get overwritten with the
current attributes of the document in memory. If the document does not
exist in the database,it will be inserted. Note that this only runs
the {before|after|around}_upsert callbacks.