如何查找列表中的所有项目 <T> 符合多个条件

Question

I have a list with products. I would like to filter the list based on multiple string objects that can contain multiple keywords.

I tried several options as you can see below:

List<Product> products = new List<Product>();
        products.Add(new Product() { Id = 1, Title = "Dit is product 1", Genre = "genre 1, genre 2, genre 4", Artist = "artist 1, artist 3"});
        products.Add(new Product() { Id = 2, Title = "Johan Bach", Genre = "genre 3, genre 4, genre 6", Artist = "artist 3, artist 4" });
        products.Add(new Product() { Id = 3, Title = "Straus is klaus", Genre = "genre 8, genre 7", Artist = "artist 9" });
        products.Add(new Product() { Id = 4, Title = "Sebastiaan buch", Genre = "genre 9, genre 2, genre 3", Artist = "artist 5, artist 6" });
        products.Add(new Product() { Id = 5, Title = "Beethoven rocks", Genre = "genre 5, genre 8, genre 11", Artist = "artist 1, artist 8" });

        string querystring = "dit buch beethove";
        string genre = "";
        string artist = "artist 9";

        var keys = querystring.Split(' ');

        Console.WriteLine("");
        Console.WriteLine("optie 1:");
        List<Product> result = products.FindAll(s => 
            s.Title.ContainsAny(keys) ||
            s.Genre.ContainsAny(genre.Split(',')) ||
            s.Artist.ContainsAny(artist.Split(','))
            );

        foreach (var product in result)
        {
            Console.WriteLine(product.Title);
        }

        Console.WriteLine("");
        Console.WriteLine("optie 2:");
        List<Product> option2 = products;
        if (querystring.Length > 0 && querystring.Split(' ').Any())
            option2 = option2.Where(s => s.Title.ContainsAny(querystring.Split(' '))).ToList();
        if (genre.Length > 0 && genre.Split(',').Any())
            option2 = option2.Where(s => s.Genre.ContainsAny(genre.Split(','))).ToList();
        if (artist.Length > 0 && artist.Split(',').Any())
            option2 = option2.Where(s => s.Artist.ContainsAny(artist.Split(','))).ToList();

        foreach (var product in option2)
        {
            Console.WriteLine(product.Title);
        }

        Console.WriteLine("");
        Console.WriteLine("optie 3:");
        List<Product> results = new List<Product>();
        if (querystring.Length > 0 && querystring.Split(' ').Any())
        {
            results = results = products.FindAll(s => s.Title.ContainsAny(keys));
        }
        if (genre.Length > 0 && genre.Split(',').Any())
        {
            results = results.Union(products.FindAll(s => s.Genre.ContainsAny(genre.Split(',')))).ToList();
        }
        if (artist.Length > 0 && artist.Split(',').Any())
        {
            results = results.Union(products.FindAll(s => s.Artist.ContainsAny(artist.Split(',')))).ToList();
        }

        foreach (var product in results)
        {
            Console.WriteLine(product.Title);
        }


        Console.ReadLine();

The result set that would be expected is the resultset of option 3: product ids 1,3,4,and 5

Is there a better way of doing what I would like to do ?

Answer 1

Since the linq statement you have there will eventually run though each item and call ContainsAny on each item you will also end up executing the split function per item.

You could however use the let keyword to let the split function been called once.

Here is a link to let keyword.

http://msdn.microsoft.com/en-us/library/bb383976.aspx

Futhermore since you are using those split functions in the bottom part of your code I would suggest you to create a variable of array type and do the split once in the top part of your code so that your linq statement and the bottom part do not need to call split various times.

If you pick this approach you will not need to use the ley keyword in linq.