I have a .NET application written in C#, and use Mongo for my database backend. One of my collections, UserSearchTerms, repeatedly (and unintentionally) has duplicate documents created.
I've teased out the problem to an update function that gets called asynchronously, and can be called multiple times simultaneously. In order to avoid problems with concurrent runs, I've implemented this code using an update which I trigger on any documents that match a specific query (unique on user and program), upserting if no documents are found.
Initially, I can guarantee that no duplicates exist and so expect that only the following two cases can occur:
- No matching documents exist, triggering an upsert to add a new document
- One matching document exists, and so an update is triggered only on that one document
Given these two cases, I expect that there would be no way for duplicate documents to be inserted through this function - the only time a new document should be inserted is if there are none to begin with. Yet over an hour or so, I've found that even though documents for a particular user/program pair exist, new documents for them are created.
Am I implementing this update correctly to guarantee that duplicate documents will not be created? If not, what is the proper way to implement an update in order to assure this?
This is the function in question:
public int UpdateSearchTerm(UserSearchTerm item)
{
_userSearches = _uow.Db.GetCollection<UserSearchTerm>("UserSearchTerms");
var query = Query.And(Query<UserSearchTerm>.EQ(ust => ust.UserId, item.UserId), Query<UserSearchTerm>.EQ(ust => ust.ProgramId, item.ProgramId));
_userSearches.Update(query, Update<UserSearchTerm>.Replace(item), new MongoUpdateOptions { Flags = UpdateFlags.Upsert });
return (int)_userSearches.Count(query);
}
Additional Information:
- I'm using mongod version 2.6.5
- The mongocsharpdriver version I'm using is 1.9.2
- I'm running .NET 4.5
- UserSearchTerms is the collection I store these documents in.
- The query is intended to match users on both userId AND programId - my definition of a 'unique' document.
- I return a count after the fact for debugging purposes.
