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Editorial Team
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Asked: 2026-06-11T18:29:29+00:00

I am using MongoDB to deserialise a document into a C# object and am

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I am using MongoDB to deserialise a document into a C# object and am having issues with ObjectID fields. This is the error I am getting:

Required element ‘LayoutId’ for property ‘LayoutId’ of class MyProject.Data.MyDocument is missing.

Which (if it doesn’t look odd anyways) does make sense because the LayoutId field IS specified:

using System;
using MongoDB.Bson;
using MongoDB.Bson.Serialization.Attributes;

namespace MyProject.Data
{
  public class MyDocument
  {

    public override ObjectId Id { get; set; }

    [BsonRequired]
    public String Name { get; set; }

    [BsonRequired]
    public ObjectId LayoutId { get; set; }

  }
}

And its populated in the database:

enter image description here

So what other aspects of the serialisation process could prevent this element from being populated? Is there a bug in a particular version of the driver? Am I using the right data type?

It should also be noted that:

  • this document was used to populate that value in the database, so it appears that only deserialisation is an issue and serialisation is fine.
  • there are other documents in the same library which have the same issue.
  • there are mongo documents/contracts in the same solution but in a different library which do NOT seem to have the same prolem,
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1 Answer

  1. Editorial Team

    Thank you Craig for attempting to solve this problem. It turns out that I had not written the question properly.

    The problem was that I was calling “SetFields()” on the result, and the fields I was requesting did not include “LayoutId”. I would have expected a more descriptive error from the driver though.

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