Saving objects with Cross-reference

larsp777

Well, you set the unique number when you register a book (Bok) or a customer (kund). It's not a Commercial application.

Book:

[Serializable()]
public class Bok : ISerializable

{
protected int isbn = 0;
protected string titel = null;
protected string author;
protected int price;
protected String isType = null;
protected Kund biblioteksKund = null;

    //egenskaper (properties). Används för att förhindra åtkomst till privata variabler.
    public int ISBN
    {
        get
        {
            return isbn;
        }
        set
        {
            isbn = value;
        }
    }

    public string Titel
    {
        get
        {
            return titel;
        }
        set
        {
            titel = value;
        }
    }

    public string Author
    {
        get
        {
            return author;
        }
        set
        {
            author = value;
        }
    }

    public int Price
    {
        get
        {
            return price;
        }
        set
        {
            price = value;
        }
    }

    public String IsType
    {
        get
        {
            return isType;
        }
        set
        {
            isType = value;
        }
    }
    
    public Kund BiblioteksKund
    {
        get
        {
            return biblioteksKund;
        }
        set
        {
            biblioteksKund = value;
        }
    }


    //Konstruktor (constructor) Metod som körs när objektet skapas. Denna körs om det inte finns parametrar.
    public Bok() 
    {
    }

    //Konstruktor med parametrar
    public Bok(int isbn, string titel, string author, int price, SerializationInfo info, StreamingContext ctxt)
    {
        ISBN = isbn;
        Author = author;
        Titel = titel;
        Price = price;
        biblioteksKund = new Kund();
        this.isbn = (int)info.GetValue("ISBN", typeof(int));
        this.author = (string)info.GetValue("Author", typeof(string));
        this.titel = (string)info.GetValue("Titel", typeof(string));
        this.price = (int)inf

Lost User

larsp777 wrote:

It's not a Commercial application.

That makes no difference.

larsp777 wrote:

Well, you set the unique number when you register a book (Bok) or a customer (kund).

What does 'skrivUt' mean? There's no list on "who" borrowed "wich" book. Remember that a ISBN-number doesn't idenitfy a specific book, but a "title". One could have multiple copies of the same title :)

Bastard Programmer from Hell :suss: If you can't read my code, try converting it here[^]

larsp777

Well, since it is run in a controlled environment I can make sure that there is only one copy with a specific ISBN. Otherwise you are right of course, ISBN identyfies a title, not a specific book. No, there is no list of who borrowed which book but each book-object "knows" who borrowed it with a reference to a customer object. protected Kund biblioteksKund = null; SkrivUt means "print" and is simply printing data about a customer but I don't think is is ever used here. (It was initially a assignment from my University made in Java.) The reason I mentioned that it is not a Commercial application was that I could made sure that no two objects are the same. But maybe that doesn't matter. Shold I use something like a GUID?

Lost User

larsp777 wrote:

The reason I mentioned that it is not a Commercial application was that I could made sure that no two objects are the same. But maybe that doesn't matter. Shold I use something like a GUID?

I dunno, and this is the place where things get complicated. Let's say I borrowed Pratchetts' book "Small Gods". You have three books of this story - how are you gonna track each book you lent? Answer; give every book a unique number (yeah, like a GUID) :)

Bastard Programmer from Hell :suss: If you can't read my code, try converting it here[^]

larsp777

Eddy Vluggen wrote:

dunno, and this is the place where things get complicated.

Let's say I borrowed Pratchetts' book "Small Gods". You have three books of this story - how are you gonna track each book you lent?

Answer; give every book a unique number (yeah, like a GUID) :)

Yes, but as I said it's a controlled environment where I make sure that there is only one copy of each book. The question is if this actually is the reason to why it doesn´t work? Or could it be that the list I am trying to save is a empty list even if I use the same name? This is the event for the button where I register the loan.

private void btnRegister_Click(object sender, EventArgs e)
{
Kund lender = null;
Bok bookToLend = null;

        //Search for chosen customer
        foreach (Kund K in CustomerList)
        {
            //Om rätt kund hittas
            if (txtPersonNr.Text.Equals(K.PersonNr.ToString()))
                lender = K; //Kunden som hittats läggs i ny variabel.
        }
        
        //If customer wasn't found.
        if (lender == null)
        {
            textBox7.Text = "Kund saknas!";
            return;
        }

        //Search for chosen book.
        foreach (Bok B in BookList)
        {
            //Om rätt bok hittas
            if (textBox6.Text.Equals(B.ISBN.ToString()))
                bookToLend = B;
        }

        //if book wasn´t found.
        if (bookToLend == null)
        {
            textBox7.Text = "Bok saknas!";
            return;
        }

                             

        if (bookToLend.BiblioteksKund == null) //If book doesn´t have its customer object set.
        {
            bookToLend.BiblioteksKund = lender; //Sets the customerobject of the book.

            lender.Loan.Add(bookToLend);    //Places the book to lend in the customers booklist.

            textBox7.Text = "Lån registrerat!";
        }

       


        
    }

Lost User

larsp777 wrote:

Or could it be that the list I am trying to save is a empty list even if I use the same name?

Looks that way; a Kund holds a list of books. When you serialize the Kund, you write the PersonNr and the Name - but not the list. Again, I'd recommend not saving a list of books, but numbers that are linked to a book.

Bastard Programmer from Hell :suss: If you can't read my code, try converting it here[^]

larsp777

Eddy Vluggen wrote:

Again, I'd recommend not saving a list of books, but numbers that are linked to a book.

Ok, Think I missunderstood you some. But I still have to save the objects somehow so I'm not really sure how that solves anything. Please explain. Edit: Realised that you probably ment the list saved in customer, not the list that holds all the books. That could be a way of avoiding cross-reference I guess.

Lost User

larsp777 wrote:

But I still have to save the objects somehow so I'm not really sure how that solves anything. Please explain.

It'd be a translation from a database-design. Right now, each book would be stored in a Kund? That means that you'd be "moving" the book-data when the book moves between different Kunds; it'd be saved in a different list. If you had three lists, life could become easier; one list to hold a collection of Kunds, one to hold the Books, and one to hold a pointer to Kund/Book combinations. In SQL, it'd be something like below;

CREATE TABLE Customer
(
Id INT IDENTITY(1,1)
PRIMARY KEY (Id)
)

CREATE TABLE Book
(
Id INT IDENTITY(1,1)
PRIMARY KEY (Id)
)

CREATE TABLE LentItems
(
CustomerId INT,
BookId INT
FOREIGN KEY (CustomerId) REFERENCES Book(Id),
FOREIGN KEY (BookId) REFERENCES Book(Id)
)

Bastard Programmer from Hell :suss: If you can't read my code, try converting it here[^]

larsp777

Eddy Vluggen wrote:

Right now, each book would be stored in a Kund? That means that you'd be "moving" the book-data when the book moves between different Kunds; it'd be saved in a different list.

This is how it works (as far as I know): Every book is stored in a list BookList and every customer is saved in CustomerList; Every customer (Kund) has it´s own list loan where references are saved to books that are borrowed by that customer. Again, this was a project I made in Java for a University-course a while back. Been trying to transfer it to C#. Every book (Bok in Swedish) has a reference to the customer who borrowed the book, so it "knows" who borrowed it. The savingpart worked fine in Java but maybe works differently in C#.

Lost User

larsp777 wrote:

Again, this was a project I made in Java for a University-course a while back. Been trying to transfer it to C#.
Every book (Bok in Swedish) has a reference to the customer who borrowed the book, so it "knows" who borrowed it. The savingpart worked fine in Java but maybe works differently in C#.

Those references are pointers; I don't think that the XmlSerializer is going to save the private loan-list on it's own.

Bastard Programmer from Hell :suss: If you can't read my code, try converting it here[^]

larsp777

Eddy Vluggen wrote:

Those references are pointers; I don't think that the XmlSerializer is going to save the private loan-list on it's own.

Yes, I know they are pointers. That is why you get cross-reference, isn´t it? Still, you could be right in that this is the problem. Edit: I think this was one thing I considered when I was trying to find the answer. Saving a list of books was no problem.

Lost User

Does the original Java-generated have it's loan-list in the XML?

Bastard Programmer from Hell :suss: If you can't read my code, try converting it here[^]

larsp777

No, I don't think I did it in XML. I saved the objects in a binary format.

Lost User

larsp777 wrote:

No, I don't think I did it in XML. I saved the objects in a binary format.

:) If you save a collection using the binary-formatter, then it'll also save the pointers. If you use XML, you'll have to save the relations yourself, or keep a list.

Bastard Programmer from Hell :suss: If you can't read my code, try converting it here[^]

larsp777

So...what do you suggest I do...

Lost User

Use the binaryformatter[^] to store it as binary data. It's that, or doing some extra work to have it correctly in XML.

Bastard Programmer from Hell :suss: If you can't read my code, try converting it here[^]