SPS101 SPS101 - 10 days ago 7
C# Question

Mongo DB 2.0 Driver C# - Upsert - Generate Object Id

I am able to update a Document if the Document Exists using the Following

var filter = Builders<Neighborhood>.Filter.Eq(x => x.Id, neighborhood.Id);

var result = await collection.ReplaceOneAsync(filter,
neighborhood,new UpdateOptions { IsUpsert = true });


[CollectionName("neighborhoods")]
[BsonIgnoreExtraElements(true)]
public class Neighborhood : IEntity<string>
{
[BsonId(IdGenerator = typeof(GuidGenerator))]
[BsonRepresentation(BsonType.ObjectId)]
public string Id { get; set; }

[BsonElement("name")]
public string Name { get; set; }
}


How do Insert a Document if the Id = NULL and I want to return the updated result.

When Inserting a New Document NULL ID, A Record is created with a NULL Id, I added [BsonId(IdGenerator = typeof(GuidGenerator))] without any luck.

What am I doing wrong so a ObjectId can be generated for new records.

Answer

C# Driver thinks that Id is already filled. You need to add settings for Id field which allows driver to generate new Id.
There are two approaches:

  1. Add attribute [BsonIgnoreIfDefault] in your Neighborhood model.
  2. Setup in code

    BsonClassMap.RegisterClassMap<Neighborhood>(x =>
    {
        x.AutoMap();
        x.GetMemberMap(m => m.Id).SetIgnoreIfDefault(true);
    });
    

I prefer the second approach because you don't need to add reference to MongoDB.

MongoDB API proposes two methods:
1) ReplaceOneAsync returns ReplaceOneResult which has UpsertedId property

var filter = Builders<Neighborhood>.Filter.Where(x => x.Name == "somthing");
var replaceResult = await collection.ReplaceOneAsync(filter, entity, new UpdateOptions { IsUpsert = true });
return replaceResult.UpsertedId;

2) FindOneAndReplaceAsync allows you to select what you want - entity before changes or after. For our task we need after

var filter = Builders<Neighborhood>.Filter.Where(x => x.Name == "somthing");
var options = new FindOneAndReplaceOptions<Neighborhood, Neighborhood>
  {
     IsUpsert = true,
     ReturnDocument = ReturnDocument.After
  };
var updatedEntity = await collection.FindOneAndReplaceAsync(filter, entity, options);