As reported in this StackOverflow question: MongoDB.Bson.BsonSerializationException after C# driver update to 3.5.0(https://stackoverflow.com/q/79780239/8017690),

I believe this bug happened after the introduction of [Serialization ignores discriminator field when checking for duplicate field names](http://jira.mongodb.org/browse/CSHARP-4040).

 

Here is how the Post owner code looks:

 
public record IdentifierSheet
{
public required string Identifier

{ get; init; }
public Security SecurityType { get; init; }
public required string Symbol { get; init; }
public Exchange Exchange { get; init; }
public string? Name { get; init; }
}

public record FutureIdentifierSheet : IdentifierSheet
{
public string Underlying { get; init; }

= string.Empty;

public required DateTime ExpirationDate { get; init; }

public required string ProductCode { get; init; }

public required DateTime YearMonth { get; init; }
}
private class SecurityTypeDiscriminatorConvention : IDiscriminatorConvention
{
public string ElementName => nameof(IdentifierSheet.SecurityType);

public Type GetActualType(IBsonReader bsonReader, Type nominalType)
{
var bookmark = bsonReader.GetBookmark();

bsonReader.ReadStartDocument();
var actualType = typeof(IdentifierSheet);

while (bsonReader.ReadBsonType() != BsonType.EndOfDocument)
{
string? name = bsonReader.ReadName();
if (name == ElementName)
{
var enumValue = (SecurityType.Security)(object)bsonReader.ReadInt32();
actualType = enumValue switch

{ SecurityType.Security.Future => typeof(FutureIdentifierSheet), SecurityType.Security.Option => typeof(OptionIdentifierSheet), _ => actualType }

;
break;
}

bsonReader.SkipValue();
}

bsonReader.ReturnToBookmark(bookmark);
return actualType;
}

public BsonValue GetDiscriminator(Type nominalType, Type actualType)
{
if (actualType == typeof(FutureIdentifierSheet))
return (int)SecurityType.Security.Future;
if (actualType == typeof(OptionIdentifierSheet))
return (int)SecurityType.Security.Option;

return (int)SecurityType.Security.NoSecurity; // fallback or base
}
}
 

My question is:

1. Is it still possible to have the discriminator as a property in the class?
2. If yes, please provide the workaround example to achieve.

 

Thanks.