I capture null value when I make a select to the database

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I capture null value when I make a select to the database

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#1 by (1 votes)
#2 by (0 votes)

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Well, the problem is: I do not capture the value that exists in the database, especially in field codsubmenu , it is only capturing null values. I leave the code.

public class Menu implements Serializable{

    private int idMenu;
    private Menu codsubmenu;

    public int getIdMenu() {
        return idMenu;
    }

    public void setIdMenu(int idMenu) {
        this.idMenu = idMenu;
    }

    public Menu getCodsubmenu() {
        return codsubmenu;
    }

    public void setCodsubmenu(Menu codsubmenu) {
        this.codsubmenu = codsubmenu;
    }      

    while(rs.next()){
        Menu menu=new Menu(); 
        menu.setIdMenu(rs.getInt("idMenu")); //en esta línea si me captura el id del menu

        // me captura null 
        menu.setCodsubmenu(menu.getCodsubmenu());
    }  
}

However, when you change the last line to:

menu.setCodsubmenu(rs.getInt("codsubmenu"));

I underline the error in this way

incompatible types: int cannot be converted to Menu**

java java-ee

asked by Libra2880 19.01.2016 в 05:49

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2 answers

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score 1 · Answer 1

Although I think there is a lack of data, this may help:

you say you capture null, and that's because you do menu.getCodsubmenu() ,

    // me captura null 
    menu.setCodsubmenu(menu.getCodsubmenu());

and this returns null because

public Menu getCodsubmenu() {
    return codsubmenu;
}

public void setCodsubmenu(Menu codsubmenu) {
    this.codsubmenu = codsubmenu;
}

is assigned and returning the same object that has not been initialized or assigned to another that was previously initialized:

private Menu codsubmenu;

getCodsubmenu() -> devuelve codesubmenu y menu.setCodsubmenu asigna el mismo objeto, al mismo objeto que no esta inicializado, quizas quiera mirar eso.

this message types: int cannot be converted to Menu** is therefore incompatible

public void setCodsubmenu(Menu codsubmenu) {
    this.codsubmenu = codsubmenu;
}

this method expects a Menu but if its name in this method menu.setCodsubmenu(rs.getInt("codsubmenu")); follows some logical getInt it may be returning an int there the error, is that you can not assign an integer in setCodsubmenu wait a Menu to assign it to codsubmenu that is of type Menu ;

score 0 · Answer 2

You have the following: Menu codsubmenu . Your submenu code is an object of class Menu . Currently, you are setting it up as follows:

menu.setCodsubmenu(menu.getCodsubmenu());

But when you create an instance of Menu , the field codsubmenu since it does not have any initialization (at least because of what you present in your code) will have as default value null , therefore that line of code have no meaning.

Now, when you try to do this:

menu.setCodsubmenu(rs.getInt("codsubmenu"));

The compilation error is explicit: you are trying to assign a variable of type Menu the value of a int .

Perhaps your problem is of order when reading the data. Since you do not thoroughly explain your underlying problem, I believe that you should first read all the data, store Menu by Menu in a container such as a list or a map and then group them the way you want. By the way, as a personal note, you may also have a design problem in your data model, because a menu should not have the id of a child menu, but rather it should have the id of the parent menu, and the only menu that does not have father id is the root of all menus.