أسئلة القسم

Question 1

Implement the singleton, strategy, and command patterns. متوسط

Answer

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();
}

Question 2

What’s the difference between Repository and Query Object patterns? متوسط

Answer

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.

Question 3

What are the advantages and disadvantages of using a Repository pattern? متوسط

Answer

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.