C#•2y ago

❔ I'm trying to implement a search function using LINQ

https://paste.mod.gg/gctsykkoclwi/3

public void SearchBook() // Defining a method and use it to access the property list and search for books
        {
            Console.WriteLine("Choose from meny: "); // Dispaly a meny for a book type
            Console.WriteLine("\n\n\t [1] Search title"
                              + "\n\t [2] Search author");
            if (int.TryParse(Console.ReadLine(), out int meny))
            switch (meny)
            {
                case 1:
                    Console.WriteLine("Search by title: ");
                    var bookTitle = Console.ReadLine();
                    var searchTitle = bookShelf.Where(x => x.Title.Contains(bookTitle));

                        if (bookTitle != null)
                        {
                            foreach (var book in searchTitle)
                            {
                                Console.WriteLine(book);
                            }
                        }
                        break;
                case 2:
                    Console.WriteLine("Search by author: ");
                    var bookAuthor = Console.ReadLine();
                        var searchAuthor = bookShelf.Where(x => x.Author.Contains(bookAuthor));

                        if (bookAuthor != null)
                        {
                            foreach (var book in searchAuthor)
                            {
                                Console.WriteLine(book);
                            }
                        }
                        break;
            }
        }

public void SearchBook() // Defining a method and use it to access the property list and search for books
        {
            Console.WriteLine("Choose from meny: "); // Dispaly a meny for a book type
            Console.WriteLine("\n\n\t [1] Search title"
                              + "\n\t [2] Search author");
            if (int.TryParse(Console.ReadLine(), out int meny))
            switch (meny)
            {
                case 1:
                    Console.WriteLine("Search by title: ");
                    var bookTitle = Console.ReadLine();
                    var searchTitle = bookShelf.Where(x => x.Title.Contains(bookTitle));

                        if (bookTitle != null)
                        {
                            foreach (var book in searchTitle)
                            {
                                Console.WriteLine(book);
                            }
                        }
                        break;
                case 2:
                    Console.WriteLine("Search by author: ");
                    var bookAuthor = Console.ReadLine();
                        var searchAuthor = bookShelf.Where(x => x.Author.Contains(bookAuthor));

                        if (bookAuthor != null)
                        {
                            foreach (var book in searchAuthor)
                            {
                                Console.WriteLine(book);
                            }
                        }
                        break;
            }
        }

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39 Replies

Pobiega•2y ago

What is the question? also, bookShelf.Where(...) will never return null, so the nullcheck isn't needed

ero•2y ago

it's not checking the returned ienumerable for null

Pobiega•2y ago

the returned ienumerable will never be null .Where cant return null

ero•2y ago

it is not checking that!

Pobiega•2y ago

you're right, what they wrote makes even less sense you are checking it for null AFTER using it

var bookTitle = Console.ReadLine();
var searchTitle = bookShelf.Where(x => x.Title.Contains(bookTitle)); // can be null here

if (bookTitle != null)
{
    // cant be null here
}

var bookTitle = Console.ReadLine();
var searchTitle = bookShelf.Where(x => x.Title.Contains(bookTitle)); // can be null here

if (bookTitle != null)
{
    // cant be null here
}

so you've already done the search before you check for null

The king of kingsOP•2y ago

Sorry! I wasn't able to search by title neither by author, because I keep miss adding the Console.ReadLine(); but now it's working.

Pobiega•2y ago

ugh not a big fan of that

The king of kingsOP•2y ago

Oh! Really. Interesting to know. Ok! I should modify the code then.

Pobiega•2y ago

yes

The king of kingsOP•2y ago

I find it a bit hard to understand these extension functions like Where() firstOrDefault() Contains()

Pobiega•2y ago

how so? Where returns all results that matched the "filter" in an IEnumerable (0..n) FirstOrDefault returns the first result that matches, or null if no item matched (null or 1)

The king of kingsOP•2y ago

I mean the docs provides too much dame informations which leads to be confused what to use and what not to use.

The king of kingsOP•2y ago

https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.firstordefault?view=net-7.0

Enumerable.FirstOrDefault Method (System.Linq)

Returns the first element of a sequence, or a default value if no element is found.

Pobiega•2y ago

there are multiple ways of calling it.

Pobiega•2y ago

https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.firstordefault?view=net-7.0#system-linq-enumerable-firstordefault-1(system-collections-generic-ienumerable((-0))-system-func((-0-system-boolean))) this one is the one that takes a predicate

Enumerable.FirstOrDefault Method (System.Linq)

Returns the first element of a sequence, or a default value if no element is found.

The king of kingsOP•2y ago

Wow, you just summarized these methods in a short and understandable way.

friedice•2y ago

Is it a requirement to search by specific type? Why not search for both? Since searchtitle is an ienum of books, when you're writing the book to the console, isn't it an object, don't you want book.Title?

Jimmacle•2y ago

iirc the assignment made him override ToString instead

The king of kingsOP•2y ago

Though the output looks a bit awkward, I mean when the user search, the output should be something like The book Harry Potter is in the Novel section

The king of kingsOP•2y ago

Didn't quite get your point? Yes, I'm trying to search either by title or author.

friedice•2y ago

why not just implement the linq to handle title or author in 1 search? is that part of the requirement

The king of kingsOP•2y ago

Nope, according to the requirements actually it's not required to search separately. But these are extra where they want me to implement for practicing sake

Enables your search to search by publication year, i.e. integer (int).
Work with access levels other than Public and Private.
Enables your program to delete all saved books.

Enables your search to search by publication year, i.e. integer (int).
Work with access levels other than Public and Private.
Enables your program to delete all saved books.

The king of kingsOP•2y ago

friedice•2y ago

it would probably be easier to implement a search that searches for all of those criterias together as an OR instead of searching seperately then

The king of kingsOP•2y ago

Ok! You're right. I can do that too. Should I just delete the author function? I think it's useless to search by publishing year too, what d y think? They have mentioned in the above that the project should be .NET Framework the problem is I use MacBook so I will need to purchase a Windows device tomorrow and configure this code in the project.

friedice•2y ago

i mean it shouldnt be too difficult to add the search for publishing year, and whatever else the book as for the prop just convert everything to string

The king of kingsOP•2y ago

Ok! You mean when the user inputs like 1999 I should convert it from int to string?

friedice•2y ago

unless you're doing maths no point to use them as raw numbers makes everything easier

The king of kingsOP•2y ago

Jimmacle•2y ago

you can probably ignore the .NET framework requirement unless this code is expected to run on a specific device

The king of kingsOP•2y ago

Ok! I totally agree with you. Other wise I'm not even intended to build apps for only Windows platform. My goal is to build cross-platform apps using .NET Maui that work on Windows & iOS and I could use my work Mac to accomplish this goal, why would I spend hundreds bucks on a new device just to finish my assignments in this course 🤷🏻‍♂️

Jimmacle•2y ago

idk, why would you

The king of kingsOP•2y ago

Yeah! Although, the online course that I'm taking currently belongs to one of the official schools in my district, so it's not just a payed local course, so I might not be granted any certificate or any validation at the end if I don't meet the course's conditions or requirements 🤔 What do you think?

Jimmacle•2y ago

i think you need to ask your teacher

The king of kingsOP•2y ago

Yep, this is the best thing I can do. Thanks a lot for your advice 🤗 I got this message from my teacher

.Net exists for several generations, if you run the .net framework, it is 4.8 which is the newest, 7 works well for most things, but on mac there is no support for windows forms in any version because it is a component connected to windows and it is this is what the course, sample assignments and the book are based on. For programming 2, it is strongly recommended that you run Windows. Unfortunately, there is no support for all alternative solutions, and then you have to Google your way. Alternatively, install virtual box or dualboot on your mac so you can run windows.

.Net exists for several generations, if you run the .net framework, it is 4.8 which is the newest, 7 works well for most things, but on mac there is no support for windows forms in any version because it is a component connected to windows and it is this is what the course, sample assignments and the book are based on. For programming 2, it is strongly recommended that you run Windows. Unfortunately, there is no support for all alternative solutions, and then you have to Google your way. Alternatively, install virtual box or dualboot on your mac so you can run windows.

@Jimmaclewhat do you think from your experience?

The king of kingsOP•2y ago

Jimmacle•2y ago

i think you should be able to figure it out at this point and if your teacher says you will need winforms then you need to run windows

The king of kingsOP•2y ago

Ok! I solved the both issues so far. I had a wrong order in the sub-class parameters that's all Regarding the Windows forms, I solved the issue by the virtualbox.

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ I'm trying to implement a search function using LINQ