Saving objects with Cross-reference

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) :)

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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.

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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)
)

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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.

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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?

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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.

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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.

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