Unable to save entities with enum with a special string converter

[Kampfmoehre]

I am trying to migrate a project to Npgsql (and EF Core) v9, however I cannot get our enums to work.

The enum looks like this:

public enum MyEnum
{
  [Description("VALUE_1")]
  Value1,

  [Description("VALUE_2")]
  Value2,
}

Previously we had this:

NpgsqlDataSourceBuilder dataSourceBuilder = new(connectionString);
dataSourceBuilder.MapEnum<MyEnum>();
NpgsqlDataSource dataSource = dataSourceBuilder.Build();

services.AddDbContextFactory<MyContext>(o =>
  {
    o.UseNpgsql(datasource);
    o.UseSnakeCaseNamingConvention();
  });

and in the Context we used this:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    ValueConverter<MyEnum, string> myEnumConverter = new(
      v => v.GetEnumDescription(),
      v => GetEnumFromDescriptionString<MyEnum>(v)); // takes the value form the Description attribute

    modelBuilder.Entity<MyEntity>(entity =>
    {
      // ...
      entity.Property(e => e.SomeThing).HasConversion(myEnumConverter);
    });
}

Following the docs I was trying to set up the following:

services.AddDbContextFactory<MyContext>(options =>
{
   options.UseNpgsql(connectionString, o => o.MapEnum<MyEnum>("my_enum"));
   options.UseSnakeCaseNamingConvention();
});

Loading entities works, but adding a new one (or changing the enum property of an existing one) fails with the following error:

---> Npgsql.PostgresException (0x80004005): 42804: column "someThing" is of type my_entity_my_enum but expression is of type text

  Exception data:
    Severity: ERROR
    SqlState: 42804
    MessageText: column "someThing" is of type my_entity_my_enum but expression is of type text
    Hint: You will need to rewrite or cast the expression.
    Position: 176
    File: parse_target.c
    Line: 584
    Routine: transformAssignedExpr

I tried different things, using DataSource, withtout Datasource, also with adding

modelBuilder.HasPostgresEnum<MyEnum>(name: "my_entity_my_enum");

but to no avail. What am I missing? I tried some things I saw in other issues around Enum mapping but failed to resolve this somehow.

My Versions are:

<PackageReference Include="EFCore.NamingConventions" Version="9.0.0" />
<PackageReference Include="Microsoft.EntityFrameworkCore" Version="9.0.2" />
<PackageReference Include="NetTopologySuite" Version="2.5.0" />
<PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL" Version="9.0.3" />
<PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL.NetTopologySuite" Version="9.0.3" />

[roji]

services.AddDbContextFactory<MyContext>(options =>
{
   options.UseNpgsql(connectionString, o => o.MapEnum<MyEnum>("my_enum");
   options.UseSnakeCaseNamingConvention();
});

The above should work, and has been tested successfully in various scenarios; can you please make sure that you're always doing that (for example, when running design-time tools, you may need have different DbContext configuration than in regular operations). Also, the code you posted above is missing a closing parentheses, so it may not be the actual code you're using.

If you can't find any issue, please try putting together a minimal, runnable repro; this will likely work, and the difference between that and your real project should help you understand where the problem is in your code. Otherwise, if you get to a minimal repro which shows the problem, you can post it here and I'll investigate.

[Kampfmoehre]

Hi @roji, thanks for the quick reply. Sorry I copied parts of the code to simplify it, sorry for the missing brace.

I am using database first approach and scaffolded the code years ago, however due to an oversight of me the write to database part was never used, instead the API of a different application that talks with the database was used to create entities. The database belongs to this other application which is using NodeJS. The column is an actual Postges Enum. I tested scaffolding again with dotnet-ef 9.0.2 and the column is just missing after that like the enum docs state.

When debugging I can see the entity instance has the enum correctly assigned to the property and the logs show it tries to insert the correct value the converter is giving: @p1='VALUE_1'

The full relevant code is

public enum MyEnum
{
  [Description("VALUE_1")]
  Value1,

  [Description("VALUE_2")]
  Value2,
}

public partial class MyEntity
{
  // ...  
  [Column("someThing", TypeName = "enum")]
  public MyEnum SomeThing { get; set; }
}

public static class EnumDescriptionExtensions
{
  public static string? GetEnumDescription(this Enum value)
  {
    Type type = value.GetType();
    string name = Enum.GetName(type, value);
    if (name != null)
    {
      FieldInfo field = type.GetField(name);
      if (field != null && Attribute.GetCustomAttribute(field, typeof(DescriptionAttribute)) is DescriptionAttribute descriptionAttribute)
      {
        return descriptionAttribute.Description;
      }
    }

    return null;
  }
}

public partial class MyContext : DbContext
{
  public MyContext(DbContextOptions<MyContext(> options)
    : base(options)
  {}

  protected override void OnModelCreating(ModelBuilder modelBuilder)
  {
    modelBuilder
      .HasPostgresEnum<MyEnum>(name: "my_entity_my_enum", new[] { "VALUE_1", "VALUE_2" })
      .HasPostgresExtension("uuid-ossp");

    ValueConverter<MyEnum, string> myEnumTypeConverter = new(
      v => v.GetEnumDescription(),
      v => GetEnumFromDescriptionString<MyEnum>(v));

    modelBuilder.Entity<MyEntity>(entity =>
    {
      entity.Property(e => e.SomeThing).HasConversion(myEnumTypeConverter);
    });
  }

  private TEnum GetEnumFromDescriptionString<TEnum>(string value)
    where TEnum : Enum
  {
    foreach (TEnum enumValue in Enum.GetValues(typeof(TEnum)))
    {
      var description = enumValue.GetEnumDescription();
      if (description == value)
      {
        return (TEnum)enumValue;
      }
    }

    throw new InvalidOperationException($"Unable to resolve enum value for string \"{value}\".");
  }
}

// DI Setup

  public static IServiceCollection ConfigureDatabases(
    this IServiceCollection services,
    IConfiguration configuration,
    IHostEnvironment environment)
  {
    bool isDev = environment.IsDevelopment();

    ConfigureDbContext<MyContext>(
      services,
      configuration,
      "MyContext",
      isDev,
      (o) => o.MapEnum<MyEnum>("my_entity_my_enum"));

    // ...

    return services;
  }

  private static void ConfigureDbContext<TContext>(
    IServiceCollection services,
    IConfiguration configuration,
    string name,
    bool enableSensitiveDataLogging = false,
    Action<NpgsqlDbContextOptionsBuilder>? npgsqlOptionsAction = null)
    where TContext : DbContext
  {
    string? connectionString = configuration.GetConnectionString(name);

    if (string.IsNullOrEmpty(connectionString))
    {
      throw new InvalidOperationException($"Unable to create a datasource: Connection string '{name}' not found.");
    }

    services.AddDbContextFactory<TContext>(options =>
    {
      options.UseNpgsql(connectionString, npgsqlOptionsAction);
      options.EnableSensitiveDataLogging(enableSensitiveDataLogging);
      options.UseSnakeCaseNamingConvention();
    });
  }

The enum was created with

CREATE TYPE "public"."my_entity_my_enum" AS ENUM('VALUE_1', 'VALUE_2');
ALTER TABLE "my_entity"
ADD "someThing" "public"."my_entity_my_enum" NOT NULL DEFAULT 'VALUE_1';

Could you guide me on how to set this up properly? Am I missing something or is this scenario not supported at all?

Edit: If I add the following line to the Context I can save the entity when I don't change the enum propertie's value without an error. But when switching to any nnon default value it fails.

      entity
        .Property(e => e.SomeThing)
        .HasColumnType("enum")
        .HasDefaultValue(MyEnum.Value1)
        .HasConversion(myEnumTypeConverter);

That's probably because Postgres is then filling in the default value, I guess?