EntityFrameworkCore - Store all enums as string even if they are defined as nullable

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1

I’m looking for an easy way to set a global configuration in my DbContext to store as string any nullable or non-nullable Enumerations.

I’ve already tried with this:

configurationBuilder.Properties<Enum>().HaveConversion<string>();

Unfortunately if the Enum is defined as Enum? the code above throws the following:

System.NullReferenceException: 'Object reference not set to an instance of an object.'
at MongoDB.EntityFrameworkCore.Serializers.ValueConverterSerializer`2.MongoDB.Bson.Serialization.IBsonSerializer.Serialize(BsonSerializationContext context, BsonSerializationArgs args, Object value)
at MongoDB.Bson.Serialization.IBsonSerializerExtensions.Serialize(IBsonSerializer serializer, BsonSerializationContext context, Object value)
at MongoDB.EntityFrameworkCore.Storage.MongoUpdate.WriteNonKeyProperties(IBsonWriter writer, IUpdateEntry entry, Func`2 propertyFilter)
at MongoDB.EntityFrameworkCore.Storage.MongoUpdate.WriteEntity(IBsonWriter writer, IUpdateEntry entry, Func`2 propertyFilter)
at MongoDB.EntityFrameworkCore.Storage.MongoUpdate.ConvertAdded(IUpdateEntry entry)
at MongoDB.EntityFrameworkCore.Storage.MongoUpdate.Create(IUpdateEntry entry)
at System.Linq.Enumerable.SelectEnumerableIterator`2.MoveNext()
at System.Linq.Enumerable.<OfTypeIterator>d__66`1.MoveNext()
at MongoDB.EntityFrameworkCore.Storage.MongoUpdateBatch.<CreateBatches>d__7.MoveNext()
at MongoDB.EntityFrameworkCore.Storage.MongoClientWrapper.<SaveUpdatesAsync>d__10.MoveNext()
at MongoDB.EntityFrameworkCore.Storage.MongoDatabaseWrapper.<SaveChangesAsync>d__3.MoveNext()
at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.<SaveChangesAsync>d__111.MoveNext()
at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.<SaveChangesAsync>d__115.MoveNext()
at Microsoft.EntityFrameworkCore.DbContext.<SaveChangesAsync>d__63.MoveNext()
at Microsoft.EntityFrameworkCore.DbContext.<SaveChangesAsync>d__63.MoveNext()
at Program.<<Main>$>d__0.MoveNext() in C:\Repos\CustomersApp\Program.cs:line 29

Code used to reproduce the issue:

<Project Sdk="Microsoft.NET.Sdk">

    <PropertyGroup>
        <OutputType>Exe</OutputType>
        <TargetFramework>net8.0</TargetFramework>
        <ImplicitUsings>enable</ImplicitUsings>
        <Nullable>enable</Nullable>
        <RootNamespace />
    </PropertyGroup>

    <ItemGroup>
        <PackageReference Include="Testcontainers.MongoDB" Version="3.9.0" />
        <PackageReference Include="MongoDB.EntityFrameworkCore" Version="8.0.3" />
    </ItemGroup>

</Project>

Program.cs

using Microsoft.EntityFrameworkCore;
using MongoDB.Bson;
using MongoDB.Driver;
using Testcontainers.MongoDb;

Console.WriteLine("Starting the test container:");

await using var mongoContainer = new MongoDbBuilder()
    .WithImage("mongo:6.0")
    .Build();

await mongoContainer.StartAsync();

Console.WriteLine("Inserting some documents:");
Console.WriteLine(mongoContainer.GetConnectionString());

var mongoClient = new MongoClient(mongoContainer.GetConnectionString());

await using (var context = new CustomersContext(mongoClient))
{
    var willow = new Customer
    {
        Id = ObjectId.GenerateNewId(),
        Name = "Willow",
        Species = null
    };

    context.Add(willow);
    await context.SaveChangesAsync();
}

Console.ReadKey();

public class CustomersContext : DbContext
{
    private readonly MongoClient _client;

    public CustomersContext(MongoClient client)
    {
        _client = client;
    }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        => optionsBuilder.UseMongoDB(_client, "efsample");

    public DbSet<Customer> Customers => Set<Customer>();
    
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
    }

    protected override void ConfigureConventions(ModelConfigurationBuilder configurationBuilder)
    {
        configurationBuilder.Properties<Enum>().HaveConversion<string>();
    }
}

public class Customer
{
    public required ObjectId Id { get; set; }
    public required string Name { get; set; }
    public Species? Species { get; set; }
}

public enum Species
{
    Human,
    Dog,
    Cat
}

EF Core version: Microsoft.EntityFrameworkCore 8.0.6
Database provider: MongoDB.EntityFrameworkCore 8.0.3
MongoDB: MongoDb.Driver 2.27.0
Target framework: .NET 8
Operating system: Visual Studio 2022 17.10.4

2

Have you found a workaround for that? I’ve stumbled the same issue