JPA Not Loading Child Objects Via One To Many Relationship
Jun 22, 2014
package com.mkyong.persistence;
import java.util.Date;
import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
[Code] ....
Everything is working fine but in my case One customer has Many orders but when i do customer.getOrders() the child objects are not loading . I dont know why.am i missing something here im using MYSQL database
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Aug 27, 2014
I want to make an application and must use strategy pattern my idea is to create a super class in this case Movie Player and three sub classer and they'll komminesera with each other using strattegy pattern, one of the sub classes is Button Panel and I want to add it to Movie Player and it was to be its child,so how can I add the butt panel to Movie Player and it shall be its children?
MoviePlayer:
import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import com.github.sarxos.webcam.WebcamPanel;
[code]....
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Oct 27, 2014
I have an assignment where I need to add an interface to an already-created program. I have an array of objects, where each object has a name, price, and priority.
In my original program (which worked), I had all of the objects in 1 class. The professor said that I should split up the name/price/priority into 3 different classes. So what I have is an array that belongs to an interface, and name/price/priority implements. But I am having trouble loading the data into the array (from another class) once I am done with loading name.
Here is what I have so far.
public class Main {
public static void main (String[] args){
Interface[] arr = new Interface[7];
Scanner keyboard = new Scanner(System.in);
System.out.println
[code]....
Line 18 in the ItemName class is giving me an error, and I know it is because arr is of type Interface, and I am trying to assign is a String. But I don't know how to do this. In my original program I was able to do arr[x].getName(); but when I do that in Main, I get errors.
how to assign to an interface array from multiple classes.
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Apr 21, 2014
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
PrintWriter pw = response.getWriter();
String connectionURL = "jdbc:mysql://localhost:3306/userdb";// userdb is the database
Connection connection;
[Code] .....
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Aug 9, 2014
I'm trying to understand the relationship between JAAS and JDBC..In WebSphere, when setting up a Dynamic cluster I have to first define the JAAS..Then, the datasource..The JAAS has one account/password and the datasource another..I'm not getting the relationship between needing both JAAS and JDBC docs.oracle.com/cd/E19225-01/820-5594/ahteo/index.html
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Mar 28, 2014
I am having difficulty with a sorting routine. I believe that the concept is valid (although not necessarily the most efficient), but I keep running into a problem. I am trying to use the compareTo function to identify the relationship between two values in an array, but it seems to have an issue with it being a comparison of two float values.
Java Code:
for (int x = 0; x < 430; x++) {
for (int y = 0; y < 430; y++) {
if (dataArray[y].compareTo(dataArray[y + 1]) > 0); {
tempOpen = dataArray[y];
[Code] ....
It gives the compile error as follows:
File: C:UsersBradDownloadsAssignment 3Calculations.java [line: 157]
Error: Cannot invoke compareTo(float[]) on the array type float[]
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May 8, 2012
I am implementing JPA hibernate simple application using one to many relationship.
Relation ship is Comapny (1)----------- Department(*)
Company.java is as follow :
package com.web.pojo;
import java.util.ArrayList;
import java.util.List;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
[Code] .....
What I am doing is , I am adding new department to existing company. After execution above code
Table created are :
1. Company table with id and name
2. Department table with deptId , deptName , compId.
so at the time adding department , it does not threw any exception but updates records in department as
1(Id),Development(DeptName),null(compId) .
I am not getting why it is not updating compId column.
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Apr 15, 2014
For example I create an object like this:
BankAccount b = new SavingsAccount();
Now lets say that I want to access a method 'addInterest()' that is in the 'SavingsAccount' class I would have to do: '((SavingsAccount)s).addInterest();'
The question I have is why do I have to cast 'b' to SavingsAccount? Isn't the actual object reference of 'b' already an instance of 'SavingsAccount' class? How does the 'BankAccount' affect the object itself? I'm really confused as to what class is truly getting instantiated and how BankAccount and SavingsAccount are both functioning to make the object 'b'.
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Jan 1, 2015
I have the following objects:
User Object:
public class User implements Serializable {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(unique = true, nullable = false)
private int id;
@OneToMany(fetch = FetchType.EAGER, mappedBy = "user", cascade = CascadeType.ALL)
private List<UserReason> userReasons;
....
Code :
public List<UserReason> getUserReasons() {
return userReasons;
}
public void setUserReasons(List<UserReason> userReasons) {
this.userReasons = userReasons;
}
public UserReason addUserReason(UserReason userReason) {
if (userReasons == null) {
userReasons = new ArrayList<UserReason>();
[Code] ....
I want to be able to add userReason to the list, and that Hibernate will automatically update the reference between the parent & child object.
When using the above code, when trying to start the server, i'm getting the error message:
Repeated column in mapping for entity: com.commit.safebeyond.model.UserReason column: userId (should be mapped with insert="false" update="false")
Please notice that i mapped the userId in UserReasonPK with insertable = false, updatable = false.
If i change it, and add this on the User property in UserReason object, server is up, but when trying to insert new User I'm getting the following error:
Hibernate: insert into UserReasons (reasonId, userId) values (?, ?)
WARN 2015-01-01 13:25:17,488 [http-nio-8080-exec-2] org.hibernate.engine.jdbc.spi.SqlExceptionHelper - SQL Error: 1452, SQLState: 23000
ERROR 2015-01-01 13:25:17,488 [http-nio-8080-exec-2] org.hibernate.engine.jdbc.spi.SqlExceptionHelper - Cannot add or update a child row: a foreign key constraint fails (`SafeBeyond`.`UserReasons`, CONSTRAINT `FK_UserReasons_Users` FOREIGN KEY (`userId`) REFERENCES `Users` (`id`))
[Code] ....
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Aug 11, 2014
I keep hearing these two term when it comes to painting in Swing, however, I'm not sure which is which. To my understanding is that the child components are the ones that already exist on screen (could be a JButton, JFrame, or custom painting) . and the parent components are the one to be added/drawn next. (hence, if we override the paintChildren() method when painting, the components that were already on the screen don't appear any more).
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May 7, 2015
I can call a child method from a main method. If I have a parent called "Assessment", a child called "Quiz", and another child called "test". Can I instantiate an object like Assessment a = new test(); and call a method in test.
I know the method can be called if I instantiate the test t = new test() but that defeats the purpose of inheritance...
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Apr 4, 2014
i have created two(displaypanel & buttonpanel) main panels in a JFrame and many child panels,one of the panel is for holding buttons and displaypanel mainly swap child panel as directed from buttonpanel, but the problem arises i cannot navigate from child panel to another child panel,
as i have made a button on one of a child panel and from button panel i add the childpanel to displaypanel.it is working but when i tried to navigate from the button which is on child panel nothing happened. "i have made a function in main form which swap the content of mainpanel (displaypanel) and in childpanel i have acces the function through object of mainform"
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May 7, 2015
I can call a child method from a main method. If I have a parent called "Assessment", a child called "Quiz", and another child called "test". Can I instinate an object like Assessment a = new test(); and call a method in test.I know the method can be called if I instinate the test t = new test() but that defeats the purpose of inheritance which I'm learning in class.
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Jan 25, 2014
I have been working on a simple problem, but I am stuck. I am trying to learn parent and child classes and how they work. The program in broken into three classes; the DemoBook class that runs the various methods, the Book class that gathers information and displays it, and finally a child class of Book (called TextBook) that just gets one piece of data and then is suppossed to return that data back to Book. However, this is not working and I know I am missing something; I believe it has to do with Set and Get methods, but I am confused with how these work.
Java Code:
public class DemoBook
{
public static void main (String[] args)
{
Book aBook = new Book();
Textbook aText = new Textbook();
[Code] .....
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Apr 19, 2015
I understand how to write a child object. I know what can access what and the order of execution of each statement, including fields, initialization blocks, and constructors. I know what will be inherited by the child and how private fields and methods are not inherited. I also know that private fields and methods in Parent are still accessible indirectly through constructors, and non-private methods. I know how to use super() and this() with or without parameters. I know when super() will be automatically inserted by the compiler and how the Object class will always be the ultimate parent class. However, I have not been able to find an explanation of exactly (or even approximately) how all this is actually put together into an actual object in memory.
For instance, if Parent.field is private and Parent.fieldGetter() is public then Child inherits fieldGetter() and can call it directly as if it is a member of Child. In fact other classes can call Child.fieldGetter() with no clue that it is not an actual member of Child. But, if fieldGetter() is now part of Child and Parent was never actually instantiated, then how is Parent.field available for Child.fieldGetter() to read? In fact, how does Parent.field exist at all? Where is it stored? (OK, I know, "on the heap.") But I want to know what it is associated with in memory. Is it treated like part of Child? Is there really a Parent object on the heap and Child simply contains references to the parts of Parent that it inherited? What?
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Sep 11, 2014
I am creating a commenting system for a side project of mine I'm building using AnuglarJS for the front-end and Spring MVC for the backend.
I am having difficulty coming up with an algorithm that will populate each comment object with a list of the comments that are responses/children of it.
The below code is what I have so far. The problem is is that it duplicates comments.
public List<Comment> getComments(int id)
{
MapSqlParameterSource params = new MapSqlParameterSource();
params.addValue("id", id);
List<Comment> allComments = jdbc.query("select * from comments where debate_id=:id", params, new RowMapper<Comment>()
[Code] ....
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Sep 29, 2014
Below mentioned classes, create object system accept in both way so what is it significant.
============
ABC obj = new Test();
Test obj = new Test();
==================
--file ABC class
class ABC{ public void disp() { System.out.println("disp() method of parent class"); }
public void abc() { System.out.println("abc() method of parent class"); } }
--file Test class
class Test extends ABC{ public void disp(){ System.out.println("disp() method of Child class"); }
public void xyz(){ System.out.println("xyz() method of Child class"); }
public static void main( String args[]) { //Parent class reference to child class object
ABC obj = new Test(); obj.disp(); obj.abc(); }}
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May 10, 2014
Is there a way to forward the text child of an anchor tag to its hyper reference?
For example, suppose I have an HTML file:
<a href = "ABC.jsp">SomeText</a>
Is there a way to send text 'SomeText' to ABC.jsp so it can be processed?
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Mar 23, 2014
sale s = new sale();
jDesktopPane1.add(s);
s.show();
says not a suitable method?
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Feb 4, 2014
I am working with a program where I am required to use a JFrame in a child class. The only way that I know how to access a JFrame is to do, example (public class Example extends JFrame), but since it is already extending the parent class, I am kind of stuck. I do not think that you can extend two separate classes, so..... I am stuck.
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Nov 29, 2014
If I lets say have an interface Animal, and I create a lot of classes with a different animal name that implement the interface Animal. Then I create an ArrayList of Animal. Then I would put in lets say Dog class into the ArrayList, which has custom methods and data that the Animal Interface doesn't have, is this data ripped away except for the methods that are put in the Animal interface? So if I would cast the Animal back to Dog, would it retain all the data that existed before it was placed in the ArrayList?
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Aug 11, 2014
I keep hearing these two term when it comes to painting in Swing, however, I'm not sure which is which. To my understanding is that the child components are the ones that already exist on screen (could be a JButton, JFrame, or custom painting) . and the parent components are the one to be added/drawn next. (hence, if we override the paintChildren() method when painting, the components that were already on the screen don't appear any more) ....
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Jul 27, 2014
I am currently working on a project where I need to return data from a database over RMI to a client who requests it. Some of the fields in the Data Object can not be seen by the client so I need to create another object to send over the network instead. The method I use is this...
public static SerializableObject createSerializableObjectFromDataObject(DataObject dataObject){
SerializableObject serializableObject = new SerializableObject();
serializableObject.setField(dataObject.getField());
serializableObject.setAnotherField(dataObject.getAnotherField());
return serializableObject;
}
Is there a better way of doing this? I am creating many subclasses DataObject which all require this static method to be implemented and I can't push it into the superclass because each one needs custom behaviour.
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Oct 31, 2014
The company entity contains companyName, Sector and Segment columns. The mapping is 3 entities (Company, Sector, Segment) where Sector and Segment are used to create a company record. Sector has a OneToMany relationship with Segment and with Company. I put the Sector and Segment values into two select menus as use these to create a Sector and Segment reference for the Company table. I'm getting the following exception:
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cannot add or update a child row:
a foreign key constraint fails (`testdummy`.`company`, CONSTRAINT `FK_COMPANY_FK_COMPANY_SECTORID` FOREIGN KEY
(`FK_COMPANY_SECTORID`) REFERENCES `sectors` (`SECTORID`))
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
I'm thinking that the problem is that since the Segment entity is a child of Sector it must be entered through an instance of Sector. Because it's being entered as a separate value I'm getting this error. The problem is Segment is defined as a Set in the Sector entity and I can't figure out how to declare Segment as an instance using its parent entity (Sector).
My code is as follows, starting with the Sector entity:
@Entity
@Table(name = "SECTORSNEW")
public class SectorsNew {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private int sectorId;
private String sectorName;
@OneToMany(cascade = CascadeType.PERSIST)
[code]....
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Jun 7, 2013
I found the following inheritance and encapsulation issue . Suppose you have a parent class with a non-static protected attribute.
package package1;
public class Parent{
protected int a = 10; // this is the non-static protected attribute in question
public static void main(String args[]){
// whatever logic
}// end Parent class
}// end main()
Now suppose you have a child class in another package and you have imported in the parent class.
package package2;
import package1.Parent;
public class Child extends Parent{
public static void main(String[] args){
Parent p = new Parent();
Child c = new Child();
System.out.println(p.a); //should print out 10 BUT DOES NOT
System.out.println(c.a); //should print out 10
}// end main()
}// end Child class
My observation is that p.a produces an error even though, to the best of my knowledge, it should not. I believe the statement "System.out.println(p.a);" should print out a 10.
Am I misunderstanding something about inheritance and encapsulation?
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Nov 15, 2011
I usually code in PHP, C++ and ActionScript.I'm trying to follow an example of how to add images to a full screen application. What he does is that he adds a JPG background image, and then 4 PNG images. I tried to do it like I always do, by writing the code by myself looking at the book. It didn't work. I searched for errors in the code, changed some things, tried different things, but it didn't work. Then I tried to use his own code, that I downloaded from his website. That didn't work either.. I tried to find another way to add an image, and I can't seem to figure out a way to implement images in any other way into this class that's written in this book.. My Java programming level isn't just high enough.
Here's the code for the file where the images load, downloaded from the authors website (I've modified the brackets and some spaces so that it becomes easier to read):
Java Code:
import java.awt.*;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
public class ImageTest extends JFrame {
public static void main(String[] args) {
DisplayMode displayMode;
[code]....
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