Implement logging and exception handling mechanism in .Net core, use well known concepts and design patterns.

Using Entity Framework Core in a .NET Core application, Consider the following scenario where you have two entities, Product and Category, with a many-to-many relationship. Each product can belong to multiple categories, and each category can have multiple products. The code below represents a simplified version:

public class Product

{

public int Id { get; set; }

public string Name { get; set; }

public ICollection<Category> Categories { get; set; }

}

public class Category

{

public int Id { get; set; }

public string Name { get; set; }

public ICollection<Product> Products { get; set; }

}

public class AppDbContext : DbContext

{

public DbSet<Product> Products { get; set; }

public DbSet<Category> Categories { get; set; }

protected override void OnModelCreating(ModelBuilder modelBuilder)

{

modelBuilder.Entity<Product>()

.HasMany(p => p.Categories)

.WithMany(c => c.Products)

.Map(pc =>

{

pc.MapLeftKey("ProductId");

pc.MapRightKey("CategoryId");

pc.ToTable("ProductCategory");

});

}

}

a. Identify potential issues in the provided code and explain them.

b. Propose improvements to address the identified issues and optimize the code.

Section 2: Angular

               Create a custom attribute directive in Angular that changes the background color of an element when hovered over. Also, implement a button in a component that, when clicked, triggers a specific action (like hiding/showing an element) using event binding.

  Given the code below, QA reports slowness in showing the user feed after deployment.

a.               Explain the possible reasons for the slowness.

b.               Introduce code improvements to improve performance.

public class FeedsBL : BaseBL

{

    public DataContext DataContext { get; set; }

    public FeedsBL(DataContext dataContext)

    {

        DataContext = dataContext;

    }

    public IEnumerable<FeedDto> GetUserFeed(int userId)

    {

        List<FeedDto> returnFeeds = new List<FeedDto>();

        var posts = GetPosts();

        var comments = GetComments();

        var likes = GetLikes();

        var userPosts = posts.Where(p => p.UserId == userId);

        foreach (var post in userPosts)

        {

            var postComments = comments.Where(c => c.Postid == post.Id);

            var postLikes = likes.Where(c => c.Postid == post.Id);

            returnFeeds.Add(new FeedDto

            {

                UserId = userId,

                Post = post,

                Comments = postComments,

                Likes = postLikes

            });

            return returnFeeds;

        }

    }

    public IEnumerable<Post> GetPosts()

    {

        return DataContext.Posts().ToList();

    }

    public IEnumerable<Comment> GetComments()

    {

        return DataContext.Comments().ToList();

    }

    public IEnumerable<Like> GetLikes()

    {

        return DataContext.Likes().ToList();

    }

}

Section 2: Angular

               Develop an Angular service that performs HTTP requests to a public API (like a weather API or a public JSON placeholder API). Then, create a component that uses this service to fetch data and display it in a formatted way.

Section 2: Angular

  Implement a simple Observable that emits values over time (like a counter). Then, create a component that subscribes to this Observable and displays its values in real-time. Additionally, include a way to unsubscribe from the Observable to demonstrate good practice in managing subscriptions.

Section 3: General Development

    Write a function in (in any code) that finds the factorial of a given integer using recursion.

Write a SQL query to retrieve all unique customers who have made purchases in the last month from a "Customers" table and an "Orders" table.

Assume you have a "Customers" table with a unique "CustomerID" and an "Orders" table with a "CustomerID" and a "OrderDate" column