StrEnum.EntityFrameworkCore

Allows to use StrEnum string enums with Entity Framework Core.

Supports EF Core 3.1–7.0

Installation

You can install StrEnum.EntityFrameworkCore using the .NET CLI:

dotnet add package StrEnum.EntityFrameworkCore

Usage

Define a string enum and an entity that uses it:

public class Sport: StringEnum<Sport>
{
    public static readonly Sport RoadCycling = Define("ROAD_CYCLING");
    public static readonly Sport MountainBiking = Define("MTB");
    public static readonly Sport TrailRunning = Define("TRAIL_RUNNING");
}

public class Race
{
    public Guid Id { get; private set; }
    public string Name { get; private set; }
    public Sport Sport { get; private set; }

    private Race()
    {
    }

    public Race(string name, Sport sport)
    {
        Id = Guid.NewGuid();
        Name = name;
        Sport = sport;
    }
}

And call the UseStringEnums() method when configuring your DB context:

public class RaceContext: DbContext
{
    public DbSet<Race> Races { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer(@"Server=.;Database=BestRaces;user id=*;pwd=*;")
            .UseStringEnums();
    }
}

That's it! EF Core is now able to deal with string enums.

Migrations

EF Core will store string enums in non-nullable string columns (NVARCHAR(MAX) in SQL Server, TEXT in Postgres).

Running dotnet ef migrations add Init will produce the following migration:

migrationBuilder.CreateTable(
        name: "Races",
        columns: table => new
        {
            Id = table.Column<Guid>(type: "uniqueidentifier", nullable: false),
            Name = table.Column<string>(type: "nvarchar(max)", nullable: false),
            Sport = table.Column<string>(type: "nvarchar(max)", nullable: false)
        },
        constraints: table =>
        {
            table.PrimaryKey("PK_Races", x => x.Id);
        });

In order to store a nullable string enum, mark the property is non-required when configuring your entity:

var race = builder.Entity<Race>();

race.Property(p => p.Sport).IsRequired(false);

Querying

EF Core will translate LINQ operations on string enums into SQL.

Let's add some races first:

var context = new RaceContext();

await context.Database.EnsureDeletedAsync();
await context.Database.EnsureCreatedAsync();

var races = new[]
{
    new Race("Chornohora Sky Marathon", Sport.TrailRunning),
    new Race("Cape Town Cycle Tour", Sport.RoadCycling),
    new Race("Cape Epic", Sport.MountainBiking)
};

await context.Races.AddRangeAsync(races);

await context.SaveChangesAsync();

And filter by a single Sport:

var trailRuns = await context.Races.Where(o => o.Sport == Sport.TrailRunning).ToArrayAsync();

That will produce the following SQL:

SELECT [r].[Id], [r].[Name], [r].[Sport]
FROM [Races] AS [r]
WHERE [r].[Sport] = N'TRAIL_RUNNING'

You can also query by multiple Sport values:

var cyclingSport = new[] { Sport.MountainBiking, Sport.RoadCycling };

var racesThatRequireABicycle = await context.Races.Where(o => cyclingSport.Contains(o.Sport)).ToArrayAsync();

Which will translate to the following SQL:

SELECT [r].[Id], [r].[Name], [r].[Sport]
FROM [Races] AS [r]
WHERE [r].[Sport] IN (N'MTB', N'ROAD_CYCLING')

Acknowledgements

Thanks to Andrew Lock for his research on using custom ValueConverterSelector.

License

Copyright © 2022 Dmitry Khmara.

StrEnum is licensed under the MIT license.