C# .NET Core Identity with Mongo DB GUID Representation Mode issue

Question

I am trying to use .NET's Core Identity, but via MongoDB instead SQL Server. I found a NuGet package that seems to fit the bill, but when I attempt to use it I get the following error:

System.MissingMethodException
  HResult=0x80131513
  Message=Method not found: 'Void MongoDB.Bson.BsonDefaults.set_GuidRepresentationMode(MongoDB.Bson.GuidRepresentationMode)'.
  Source=MongoDbGenericRepository
  StackTrace:
   at MongoDbGenericRepository.MongoDbContext.SetGuidRepresentation(GuidRepresentation guidRepresentation)
   at MongoDbGenericRepository.MongoDbContext.InitializeGuidRepresentation()
   at MongoDbGenericRepository.MongoDbContext..ctor(String connectionString, String databaseName)
   at Microsoft.Extensions.DependencyInjection.MongoDbIdentityBuilderExtensions.AddMongoDbStores[TUser,TRole,TKey](IdentityBuilder builder, String connectionString, String databaseName)
   at AspNetCore.Identity.MongoDbCore.Extensions.ServiceCollectionExtension.ConfigureMongoDbIdentity[TUser,TRole,TKey](IServiceCollection services, MongoDbIdentityConfiguration mongoDbIdentityConfiguration, IMongoDbContext mongoDbContext)

The NuGet package is:

I registered the GUID Representation Mode in the Program.cs as follows (I needed this for the other MongoDB operations requiring a GUID to be stored as the _id:

BsonSerializer.RegisterSerializer(new GuidSerializer(GuidRepresentation.Standard)); // For MongoDB Guis

And in the later part of the Program.cs I have the following registration of the MongoDbIdentity service as follows:

var mongoDbSettings = builder.Configuration.GetSection(nameof(MongoDBSettings)).Get<MongoDBSettings>();

var mongoDbIdentityConfiguration = new MongoDbIdentityConfiguration
{
    MongoDbSettings = new MongoDbSettings
    {
        ConnectionString = mongoDbSettings?.ConnectionString,
        DatabaseName = mongoDbSettings?.DatabaseName,
        
    },
    IdentityOptionsAction = options =>
    {
        options.Password.RequireDigit = true;
        options.Password.RequiredLength = 8;
        options.Password.RequireNonAlphanumeric = true;
        options.Password.RequireUppercase = true;
        options.Password.RequireLowercase = true;

        // Lockout settings
        options.Lockout.DefaultLockoutTimeSpan = TimeSpan.FromMinutes(30);
        options.Lockout.MaxFailedAccessAttempts = 20;

        // ApplicationUser settings
        options.User.RequireUniqueEmail = false;
        options.User.AllowedUserNameCharacters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789@.-_";
    }
};
builder.Services.ConfigureMongoDbIdentity<ApplicationUser, ApplicationRole, Guid>(mongoDbIdentityConfiguration);

The exception is triggered by this line:

builder.Services.ConfigureMongoDbIdentity<ApplicationUser, ApplicationRole, Guid>(mongoDbIdentityConfiguration);

I followed the following example:

https://www.yogihosting.com/aspnet-core-identity-mongodb/

My questions are:

Is there something I need to do to help the package recognize the BSON GUID?
The package seems fairly new (2024 last updated) but is anyone else using it?
Is there a better way to do this? I wanted to be somewhat standard, but I could implement my own Identity service, I just wanted to be somewhat standard to use the Authorization/Authentication annotations.

Markus · Accepted Answer · 2025-04-25 06:45:36Z

2

The problem is that you are using AspNetCore.Identity.MongoDB while referencing MongoDB.Driver version 3+. The property that is accessed has been removed in driver version 3 hence the exception.

How to solve this:

Best, but slowest: try to get an updated version of the package, maybe by creating a PR or filing an issue in the project
Quick fix: downgrade your MongoDB driver to version 2.x which is not optimal, but should fix the issue.
I have seen that there are various projects that implement ASP.NET Core Identity with MongoDB, maybe there is an alternative package that works with driver version 3.x

answered Apr 25 at 6:45

Markus

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Thalys · Accepted Answer · 2025-05-30 13:57:24Z

1

Ensure that all your model classes that use Guid properties (like Id, UserId, etc.) are annotated with [BsonRepresentation(BsonType.'Type')].

This tells the MongoDB driver to store the Guid as a string in the database and to correctly convert it when reading from or writing to MongoDB. MongoDB does not have a native data type for Guid.

[BsonRepresentation(BsonType.String)]
public Guid Id { get; set; }

edited May 30 at 13:57

answered May 30 at 13:54

Thalys

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