EF Core FirstOrDefault returns null even if entity exists

December 9, 2024

I am facing an issue where I cant fetch an entity when using .FirstOrDefaultAsync() with a GUID as the primary key.
If I fetch all entries first and then run .FirstOrDefault it works.

The entity in question also exists when inspecting the DbContext.

Using .NET 8.0 with Entity Framework 9.0.0 and Sqlite

public async Task AddClaim(User user, Guid claimId)
{    
    // returns null
    var claim = await context.Claims.FirstOrDefaultAsync(x => x.Id == claimId);

    // this works
    var claims = await context.Claims.ToListAsync();
    var localClaim = claims.FirstOrDefault(x => x.Id == claimId);
    
    // this throws UniqueContrain exception
    context.Claims.Add(new Domain.Entities.Claim() { Id = claimId });

    // ...
}

public class Claim
{
    public Guid Id { get; set; }
    public string Name { get; set; } = null!;
    public string Value { get; set; } = null!;
    public ICollection<User> Users { get; set; } = null!;
}

>Solution :

SQLite can store Guid values as TEXT or BLOB

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Claim>()
        .Property(c => c.Id)
        .HasConversion(v => v.ToString(), v => Guid.Parse(v));
}

This should work.