ef-core

Entity Framework Core Patterns

DbContext Configuration

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

    public DbSet<User> Users => Set<User>();

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.ApplyConfigurationsFromAssembly(typeof(AppDbContext).Assembly);
    }
}

Entity Configuration

public sealed class UserConfiguration : IEntityTypeConfiguration<User>
{
    public void Configure(EntityTypeBuilder<User> builder)
    {
        builder.ToTable("Users");
        builder.HasKey(x => x.Id);
        builder.Property(x => x.Email).HasMaxLength(256).IsRequired();
        builder.HasIndex(x => x.Email).IsUnique();
    }
}

Repository Pattern

public interface IUserRepository
{
    Task<User?> GetByIdAsync(Guid id, CancellationToken ct = default);
    Task<User?> GetByEmailAsync(string email, CancellationToken ct = default);
    void Add(User user);
    void Remove(User user);
}

Query Best Practices

Scenario	Approach
Read-only queries	.AsNoTracking()
Single item	.FirstOrDefaultAsync() (not .SingleOrDefaultAsync() unless uniqueness matters)
Exists check	.AnyAsync()
Count	.CountAsync()
Projections	.Select(x => new Dto { ... }) — avoid loading full entities
Pagination	.Skip(n).Take(m) after ordering

Anti-Patterns to Avoid

• NEVER use .ToList() then LINQ — query in database
• NEVER load navigation properties you don't need
• NEVER use Include() for read-only projections — use Select()
• NEVER call SaveChangesAsync() multiple times per operation

Migrations

dotnet ef migrations add MigrationName --project src/Infrastructure --startup-project src/Api
dotnet ef database update --project src/Infrastructure --startup-project src/Api

• ALWAYS review generated migrations before applying
• NEVER modify existing migrations after they're applied