在Mongodb .Net驱动程序中应用upsert

Question

I need to perform atomic "if not exist add" logic, else do nothing, to do this I am using Upsert.

My model:

  public class Person
  {
    [BsonId]
    public Guid Id { get; set; }
    public string Name { get; set; }
    public string Title { get; set; }
    public DateTime ReceivedAt { get; set; }
    public List<Person> Children { get; set; }
  }

my code:

var person = new Person() { Id = Guid.NewGuid(), Name = "name", Title = "title", ReceivedAt = DateTime.Now };
var result = context.People.FindOneAndUpdateAsync<Person>(
           x => x.Title == person.Title && x.Name == person.Name && x.ReceivedAt <= person.ReceivedAt + TimeSpan.FromMinutes(1),
           Builders<Person>.Update.Combine(),
           new FindOneAndUpdateOptions<Person>() { IsUpsert = true });

The above is not inserting the document is not exist, what I am doing wrong? do I need to set something other than IsUpsert?

Answer 1

In your code result is of type Task<Person> and you miss await here and that's why you don't observe that Exception is thrown. When you change your code to:

var result = col.FindOneAndUpdateAsync<Person>(
                   x => x.Title == person.Title && x.Name == person.Name && x.ReceivedAt <= person.ReceivedAt + TimeSpan.FromMinutes(1),
                   Builders<Person>.Update.Combine(),
                   new FindOneAndUpdateOptions<Person>() { IsUpsert = true })
               .GetAwaiter().GetResult(); // or await in front of invocation

You'll get an ArgumentException with following message:

Additional information: Updates must have at least 1 update operator.

So you can't have empty update. To fix that you can for instance repeat Title property, which works exactly the same way as your code expects.

var result = col.FindOneAndUpdateAsync<Person>(
                   x => x.Title == person.Title && x.Name == person.Name && x.ReceivedAt <= person.ReceivedAt + TimeSpan.FromMinutes(1),
                   Builders<Person>.Update.Set(x => x.Title, person.Title),
                   new FindOneAndUpdateOptions<Person>() { IsUpsert = true }).GetAwaiter().GetResult();

ReceivedAt will not be added since your lambda expression translates to $lte which is not an equality comparison (check docs here ). You should explicitly define that value in update part.

The update creates a base document from the equality clauses in the parameter, and then applies the update expressions from the parameter. Comparison operations from the will not be included in the new document.