efcore-patterns

EF Core Patterns

DbContext design

public sealed class AppDbContext : DbContext
{
    public AppDbContext(DbContextOptions<AppDbContext> options) : base(options) { }

    public DbSet<User> Users => Set<User>();
    public DbSet<Order> Orders => Set<Order>();
    public DbSet<OrderLine> OrderLines => Set<OrderLine>();

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        // Discover all IEntityTypeConfiguration<T> in the assembly automatically
        modelBuilder.ApplyConfigurationsFromAssembly(typeof(AppDbContext).Assembly);
    }
}

Use ApplyConfigurationsFromAssembly — it discovers all IEntityTypeConfiguration<T> implementations automatically, avoiding the need to register each entity manually in OnModelCreating.

Use DbSet<T> expression-bodied properties (=> Set<T>()) to avoid null warnings and simplify the class.

Entity configuration — Fluent API

public sealed class OrderConfiguration : IEntityTypeConfiguration<Order>
{
    public void Configure(EntityTypeBuilder<Order> builder)
    {
        builder.ToTable("orders");
        builder.HasKey(o => o.Id);

        builder.Property(o => o.Status)
               .HasConversion<string>()   // store enum as string for readability
               .HasMaxLength(50)
               .IsRequired();

        builder.Property(o => o.Total)
               .HasPrecision(18, 2)
               .IsRequired();

        builder.Property(o => o.CreatedAt)
               .IsRequired();

        builder.Property(o => o.Notes)
               .HasMaxLength(1000)
               .IsRequired(false);

        builder.HasIndex(o => o.CustomerId);
        builder.HasIndex(o => new { o.Status, o.CreatedAt });

        builder.HasOne(o => o.Customer)
               .WithMany(c => c.Orders)
               .HasForeignKey(o => o.CustomerId)
               .OnDelete(DeleteBehavior.Restrict);   // don't cascade-delete orders with customer

        builder.HasMany(o => o.Lines)
               .WithOne(l => l.Order)
               .HasForeignKey(l => l.OrderId)
               .OnDelete(DeleteBehavior.Cascade);   // deleting an order removes its lines
    }
}