[MongoDB .NET Driver] Upsert & SetOnInsert sample ref: http://qiita.com/SHUAI/items/e1f9bde6eb118de0fb88

file0.cs

public class Member 
{
    public ObjectId Id { get; set; }

    public string PersonId { get; set; }

    public string Name { get; set; }

    public int Gender { get; set; }

    public string Phone { get; set; }

    public int ZipCode { get; set; }

    public string Address { get; set; }

    public DateTime CreatedDate { get; set; }

    public DateTime ModifiedDate { get; set; }
}

file1.cs

var filter = Builders<Member>.Filter.Eq<string>(m => m.PersonId, id);
var updates = new List<UpdateDefinition<Member>>();
updates.Add(Builders<Member>.Update.Set(m => m.Phone, phone));
updates.Add(Builders<Member>.Update.Set(m => m.ModifiedDate, DateTime.Now));
// SetOnInsert: 只有新增時才會寫入其值
updates.Add(Builders<Member>.Update.SetOnInsert(m => m.CreatedDate, DateTime.Now));
// Upsert: UpdateOptions -> IsUpsert = true
var result = db.GetCollection<Member>(colName).UpdateOneAsync(filter, Builders<Member>.Update.Combine(updates), new UpdateOptions() { IsUpsert = true }).ConfigureAwait(continueOnCapturedContext: false);