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الكل سهل متوسط صعب
What is SOLID? Can you elaborate on each SOLID acronym? سهل

A set of 5 object-oriented design principles:

Acronym Principle Meaning (simple)
S Single Responsibility Principle A class should have only one reason to change.
O Open/Closed Principle Open for extension, closed for modification.
L Liskov Substitution Principle Subclasses should be substitutable for base classes.
I Interface Segregation Principle Many small, specific interfaces are better than one large one.
D Dependency Inversion Principle Depend on abstractions, not on concrete implementations.
Name design patterns and principles you know and how they are utilized in .NET Framework. سهل
  • Creational Patterns:
    • Singleton: IConfiguration or IHttpClientFactory as singleton in DI.
    • Factory: DbContextFactory creates EF Core contexts.
  • Structural Patterns:
    • Adapter: Wrapping a third-party API in your own interface.
    • Decorator: Adding behavior to services without changing them (middleware).
  • Behavioral Patterns:
    • Strategy: PasswordHasher implementations or ILoggerProvider.
    • Command: MediatR library in .NET implements Command pattern for CQRS.
  • Principles:
    • SOLID, DRY, KISS, YAGNI
Implement the singleton, strategy, and command patterns. متوسط

Singleton:

public sealed class AppSettings {
    private static readonly Lazy<AppSettings> _instance =
        new Lazy<AppSettings>(() => new AppSettings());
    public static AppSettings Instance => _instance.Value;
    private AppSettings() {}
}

Strategy:

public interface IDiscountStrategy { decimal Apply(decimal price); }
public class NoDiscount : IDiscountStrategy { public decimal Apply(decimal p) => p; }
public class ChristmasDiscount : IDiscountStrategy { public decimal Apply(decimal p) => p * 0.8m; }

public class PriceCalculator {
    private readonly IDiscountStrategy _strategy;
    public PriceCalculator(IDiscountStrategy strategy) { _strategy = strategy; }
    public decimal Calculate(decimal price) => _strategy.Apply(price);
}

Command:

public interface ICommand { void Execute(); }
public class SaveOrderCommand : ICommand {
    public void Execute() { /* save order */ }
}
public class Invoker {
    public void Run(ICommand command) => command.Execute();
}
What’s the difference between Repository and Query Object patterns? متوسط
Aspect Repository Pattern Query Object Pattern
Purpose Abstracts persistence and CRUD operations. Encapsulates a single complex query.
Scope Whole aggregate or entity set. One-off or reusable query logic.
Usage IRepository<User> handles Add, Update, Delete, Get. UserByRoleQuery returns users by role.
What are the advantages and disadvantages of using a Repository pattern? متوسط

Advantages:

  • Centralized data access logic.
  • Easier to mock/test.
  • Decouples app from EF Core or other ORMs.

Disadvantages:

  • Can become bloated with many methods.
  • Sometimes duplicates EF Core features (extra layer).
  • Harder to optimize queries if overly generic.
What is CQRS, and in which scenarios may it be beneficial? صعب

CQRS = Command Query Responsibility Segregation. Separate write (commands) from read (queries) models.

Benefits:

  • Scalability (read and write can scale independently).
  • Clearer design when business rules differ between reads/writes.

Scenarios:

  • Complex domains with heavy read/write asymmetry.
  • Event sourcing or high performance read models.
What is the difference between an event and a command (like in CQRS)? صعب
Aspect Command Event
Intent Ask to do something (imperative). Notification something happened (past tense).
Responsibility Has a handler; expects action. May have multiple subscribers; no action guaranteed.
Timing Future action Already occurred
What is the Saga pattern? صعب

Orchestration for long-running or distributed transactions. Breaks a business process into a series of steps (local transactions) coordinated via messages. Handles compensating actions if a step fails.

What is Clean Architecture in .NET Core? صعب

An approach where business logic is independent of frameworks and UI.

Layers:

  • Domain (entities, core logic)
  • Application (use cases, interfaces)
  • Infrastructure (EF Core, external services)
  • Presentation (Web API, UI)

Dependency rule: outer layers depend inward.

Explain Monolithic vs Microservices architecture. صعب
Aspect Monolith Microservices
Deployment Single unit Independent services
Scaling Entire app scales Scale each service individually
Boundaries Shared database/code Each service has own DB, clear boundaries
Complexity Simple to start Higher operational complexity

When to choose:

  • Monolith for simple apps, low team size.
  • Microservices for large apps needing independent scaling/deployment.