C# Net.Core Object.Equals() 返回 false 即使两个对象相同

Question

I am trying to return a list of recommended movies based on a client's favorite movies genres without including those that are already his favorites.

So, here is my Movie object

 public class Movie
{
    /// <summary>
    /// Movie's title
    /// </summary>
    public string Title { get; set; }
    
    /// <summary>
    /// Movie's gengres list
    /// </summary>
    public List<string> Genres { get; set; }

    private int HashCode 
    {
        get
        {
            return this.Title.GetHashCode();
        }
    }

    /// <summary>
    /// Public default constructor. Initializes an empty Movie object
    /// </summary>
    public Movie()
    {
        Genres = new List<string>();
    }

    /// <summary>
    /// Initializes a Movie object with a given title
    /// </summary>
    /// <param name="title">Movie title</param>
    public Movie(string title)
    {
        Title = title;
        Genres = new List<string>();
    }

    /// <summary>
    /// Override ToString function
    /// </summary>
    /// <returns>Movie's title</returns>
    public override string ToString()
    {
        return Title;
    }

    public override int GetHashCode()
    {
        return HashCode;
    }

    public override bool Equals(object obj)
    {
        if ((obj == null) || !this.GetType().Equals(obj.GetType()))
        {
            return false;
        }
        else
        {
            Movie movie = (Movie)obj;
            return (HashCode == movie.HashCode);
        }
    }
}

And here is my Client object

public class Client
{
    /// <summary>
    /// Client's First Name
    /// </summary>
    public string FirstName { get; set; }

    /// <summary>
    /// Client's Last Name
    /// </summary>
    public string LastName { get; set; }

    /// <summary>
    /// Client's full name
    /// </summary>
    public string FullName 
    {
        get
        {
            return $"{FirstName} {LastName}";
        }
    }

    /// <summary>
    /// Client's favorite movies
    /// </summary>
    public List<Movie> FavoriteMovies { get; set; }

    /// <summary>
    /// Public default constructor. Initializes an empty client
    /// </summary>
    public Client()
    {
        FavoriteMovies = new List<Movie>();
    }

    /// <summary>
    /// Initializes a client object with a given name
    /// </summary>
    /// <param name="firstName">Client's first name</param>
    /// <param name="lastName">Client's last name</param>
    public Client(string firstName, string lastName)
    {
        FirstName = firstName;
        FavoriteMovies = new List<Movie>();
    }

    /// <summary>
    /// Initializes a client object with given name and list of favorite movies
    /// </summary>
    /// <param name="firstName">Client's first name</param>
    /// <param name="lastName">Client's last name</param>
    /// <param name="favoriteMovies">Client's list of favorite movies</param>
    public Client(string firstName, string lastName, List<Movie> favoriteMovies)
    {
        FirstName = firstName;
        LastName = lastName;
        FavoriteMovies = favoriteMovies;
    }

    /// <summary>
    /// Override ToString function that will return Client's full name
    /// </summary>
    /// <returns>Client's full name</returns>
    public override string ToString()
    {
        return FullName;
    }

Here's my movie list

        Movies = new List<Movie>();

        Movie movie1 = new Movie("Untitled Screenplay, adapted from the book, the Price of Fame, the biography of Dennis Price. Written by Eliane Parker and Gareth Owen.");
        movie1.Genres.Add("Action");
        Movies.Add(movie1);

        Movie movie2 = new Movie("Cannery Row");
        movie2.Genres.Add("Comedy");
        movie2.Genres.Add("Drama");
        movie2.Genres.Add("Romance");
        Movies.Add(movie2);

        Movie movie3 = new Movie("Body Melt");
        movie3.Genres.Add("Comedy");
        movie3.Genres.Add("Horror");
        movie3.Genres.Add("Sci-Fi");
        Movies.Add(movie3);

        Movie movie4 = new Movie("Ghost Lab");
        movie4.Genres.Add("Drama");
        movie4.Genres.Add("Horror");
        movie4.Genres.Add("Thriller");
        Movies.Add(movie4);

        Movie movie5 = new Movie("Biography: WWE Legends Biography: Booker T");
        movie5.Genres.Add("Action");
        Movies.Add(movie5);

        Movie movie6 = new Movie("Zombie Wars");
        movie6.Genres.Add("Action");
        Movies.Add(movie6);

        Movie movie7 = new Movie("Delitto in Formula Uno");
        movie7.Genres.Add("Comedy");
        movie7.Genres.Add("Crime");
        movie7.Genres.Add("Thriller");
        Movies.Add(movie7);

        Movie movie8 = new Movie("The Long and Winding Road");
        movie8.Genres.Add("Comedy");
        movie8.Genres.Add("Drama");
        Movies.Add(movie8);

And my client would be like this

        Client client2 = new Client("Belinda", "Reed");
        client2.FavoriteMovies.Add(movie2);
        client2.FavoriteMovies.Add(movie7);
        Clients.Add(client2);

That mean that client2 favorite movies titles Cannery Row (which is movie2 ) and Delitto in Formula Uno (which is movie7 ). Favorite genres list would be

"Comedy"
"Drama"
"Romance"
"Crime"
"Thriller"

And the function that will return the movie recommendations is

    public static List<Movie> MovieRecommendationsByClient(Client client, List<Movie> moviesCatalog)
    {
        var recommendations = moviesCatalog
            .Where(movie => client.FavoriteMovies
                                    .Any(cm => (!cm.Equals(movie)
                                        && cm.Genres.Intersect(movie.Genres).Any()))).ToList();


        return recommendations;
    }

In theory, movie recommendations based on client's favorite movies genres list without including those that he already likes should be

"Body Melt"
"Ghost Lab"
"The Long and Winding Road"

But the assertion is failing because the return list is also including "Cannery Row" and "Delitto in Formula Uno"

I also tried in this way with the same results:

            var recommendations = from movie in moviesCatalog
                              from clientMovie in client.FavoriteMovies
                              where !clientMovie.Equals(movie) && movie.Genres.Intersect(clientMovie.Genres).Any()
                              group movie by movie into moviesGroup
                              select moviesGroup.Key;

I've also tried comparing Movie Title properties or GetHashCode() function without any success.

When I am debugging the test, I can see that Equals(movie) returns the result that I am expecting, so I am thinking I am doing something wrong at the LINQ query.

Any help would be really appreciated

Answer 1

First you could to exclude movies you alread have in the client list and then filter by genres combination

It works:

   var recommendations = moviesCatalog.Except(client.FavoriteMovies)
            .Where(movie => client.FavoriteMovies
            .Any(cm => cm.Genres.Intersect(movie.Genres).Any())).ToList();