I have the following classes representing that one Account can have multiple Profiles (simplified for easier understanding):

public record ProfileId(string Value);
public record AccountId(string Value);
public record UserId(string Value);

public class Profile
{
    private Profile() { }
    private Profile(ProfileId id, UserId userId, Account account)
    {
        Id = id;
        UserId = userId;
        Account = account;
    }

    public ProfileId Id { get; private set; }
    public UserId UserId { get; private set; }
    public Account Account { get; private set; }
}

public class Account
{
    private Account() { }
    private Account(AccountId id, string name)
    {
        Id = id;
        Name = name;
    }

    public AccountId Id { get; private set; }
    public string Name { get; private set; }
    private readonly List<Profile> _profiles = new();
    public IReadOnlyCollection<Profile> Profiles =>_profiles.AsReadOnly();
}

This is the code for the Profile entity type configuration:

        builder.ToTable("profiles");
        builder.HasOne(profile => profile.Account)
            .WithMany(account => account.Members)
            .HasForeignKey("account_id")
            .IsRequired();
        builder.Property(profile => profile.UserId)
            .HasColumnName("user_id")
            .IsRequired();
        builder.HasKey("user_id", "account_id");

… and this is the one for Account:

        builder.ToTable("accounts");
        builder.HasKey(account => account.Id);

I want a composite key for the table Profile on “user_id” and “account_id”, but EF gives me this error.

Unable to create a ‘DbContext’ of type ‘AppDbContext’. The exception ‘The property ‘user_id’ cannot be added to the type ‘Profile’ because no property type was specified, and there is no corresponding CLR property or field. To add a shadow state property, the property type must be specified.’ was thrown while attempting to create an instance.

How can you configure the Profile entity with EF to achieve this goal?