C# MongoDB BsonDocument not getting serialized to custom class using BsonSerializer

Question

I am having an issue with serializing BsonDocuments using BsonSerializer.

I am using var bsonDoc = collection.Find(...) to pull a single document from a MongoDB database. I then try to serialize it using var strongTypedDocument = BsonSerializer.Deserialize<MainSDocument>(bsonDoc);

Here is the BsonDocument

   { 
      "MainSPayload" : 
        { 
           "GDeets" : { "Id" : 0, "GSerial" : "XX123XX123" }
        }
   }

Here are the C# classes

[JsonObject(MemberSerialization.OptIn)]
[BsonIgnoreExtraElements]
public class MainSDocument
{
    [JsonProperty(Required = Required.Always)]
    public MainState MainSPayload
    {
        get; set;
    }
}

[JsonObject(MemberSerialization.OptIn)]
public class MainState 
{
    [JsonProperty(Required = Required.Always)]
    public GDetails GDeets
    {
        get; set;
    }
}

public class GDetails 
{
    public int Id
    {
        get; set;
    }

    public string GSerial
    {
        get; set;
    }
}

The error I am getting is: FormatException: An error occurred while deserializing the GDetails property of class MainState : Element 'Id' does not match any field or property of class GDetails .'

Why is this happening? Why doesn't the element Id match the int element Id in the GDetails class?

please show us the class `GroupInfo` – jazb Dec 01 '21 at 07:16 — jazb, Dec 01 '21 at 07:16
@Jazb oops! that was a typo :) corrected it. – user20358 Dec 01 '21 at 07:22 — user20358, Dec 01 '21 at 07:22

dododo · Accepted Answer · 2021-12-07T12:06:46.087

Serialization for Id field has a special workflow that effectively converts this value into how the server side represents it: _id. To workaround it you can use:

        BsonClassMap.RegisterClassMap<GDetails>(c =>
        {
            c.AutoMap();
            c.UnmapField(u => u.Id); // remove default _id workflow 
            c.MapField(u => u.Id); // add a simple Id field
        });

or simpler:

        BsonClassMap.RegisterClassMap<GDetails>(c =>
        {
            c.AutoMap();
            c.SetIdMember(null);
        });

UPDATE: There is a bit more flexible way. You can configure a new convention and set for what types you will need using it:

        var customPack = new ConventionPack();
        customPack.Add(new NoIdMemberConvention());
        ConventionRegistry.Register("NoIdConvention", customPack, t => t == typeof(GDetails));

also instead the above, you can just add BsonNoId attribute to your class:

    [BsonNoId]
    public class GDetails
    {
        public int Id
        {
            get; set;
        }

        public string GSerial
        {
            get; set;
        }
    }

Thanks. Is there a more generic way to set this for all Id fields without having to put those 5 lines of code for each class? — user20358, Dec 06 '21 at 23:43
I don't think so, and it's required not for each class, only for cases where `Id` means not server side `_id` — dododo, Dec 06 '21 at 23:56

C# MongoDB BsonDocument not getting serialized to custom class using BsonSerializer

1 Answers1