WriteConcernResult result null mongodb - mongodb

Question

When trying to update with mongodb by using the below code my result is getting null: in C#
public bool UpdateContact(string id, Contact item)
{
IMongoQuery query = Query.EQ("_id", id);
item.LastModified = DateTime.UtcNow;
IMongoUpdate update = Update
.Set("Email", item.Email)
.Set("LastModified", DateTime.UtcNow)
.Set("Name", item.Name)
.Set("Phone", item.Phone);
WriteConcernResult result = _contacts.Update(query, update);
return result.UpdatedExisting;
}

Answer 1

If you're not using the new connection style for the C# driver (and likely other drivers), your connection may be configured to not have a WriteConcern by default.
If there's no WriteConcern configured, the C# API will return a null as the result for the code you provided (see Update for more info)
For example, if your connection is like this:
var connectionString = "mongodb://localhost";
var server = MongoServer.Create(connectionString); // deprecated
var database = server.GetDatabase("test"); // WriteConcern defaulted to Unacknowledged
That would be configured to for no write concern.
You should be using this style (as of the C# 1.7 driver):
var connectionString = "mongodb://localhost";
var client = new MongoClient(connectionString);
var server = client.GetServer();
var database = server.GetDatabase("test"); // WriteConcern defaulted to Acknowledged
The difference is that you need to use the MongoClient class (and get the MongoServer and the MongoDatabase from that object instance).