qr code scanner java app Domain models and metadata in Java

Print QR Code in Java Domain models and metadata

Domain models and metadata
QR Code JIS X 0510 Generation In Java
Using Barcode maker for Java Control to generate, create QR Code JIS X 0510 image in Java applications.
www.OnBarcode.com
Denso QR Bar Code Recognizer In Java
Using Barcode reader for Java Control to read, scan read, scan image in Java applications.
www.OnBarcode.com
What are the requirements for JPA entity classes The good news is that so far, all the conventions we ve discussed for POJOs are also requirements for JPA entities. You have to apply some additional rules, but they re equally simple; we ll come back to them later. Now that we ve covered the basics of using POJO persistent classes as a programming model, let s see how to handle the associations between those classes.
Encoding DataMatrix In Java
Using Barcode creation for Java Control to generate, create Data Matrix image in Java applications.
www.OnBarcode.com
Barcode Generation In Java
Using Barcode creator for Java Control to generate, create Barcode image in Java applications.
www.OnBarcode.com
Implementing POJO associations
Drawing Linear In Java
Using Barcode generation for Java Control to generate, create 1D Barcode image in Java applications.
www.OnBarcode.com
Print Code-39 In Java
Using Barcode creation for Java Control to generate, create Code 3 of 9 image in Java applications.
www.OnBarcode.com
You use properties to express associations between POJO classes, and you use accessor methods to navigate from object to object at runtime. Let s consider the associations defined by the Category class, as shown in figure 3.3. As with all our diagrams, we left out the associationrelated attributes (let s call them parentCategory and Figure 3.3 Diagram of the Category childCategories) because they would clutter the illustra- class with associations tion. These attributes and the methods that manipulate their values are called scaffolding code. This is what the scaffolding code for the one-to-many self-association of Category looks like:
QR Code Drawer In Java
Using Barcode drawer for Java Control to generate, create QR Code image in Java applications.
www.OnBarcode.com
Generate ANSI/AIM I-2/5 In Java
Using Barcode generator for Java Control to generate, create Interleaved 2 of 5 image in Java applications.
www.OnBarcode.com
public class Category { private String name; private Category parentCategory; private Set childCategories = new HashSet(); public Category() { } ... }
Make QR Code ISO/IEC18004 In Java
Using Barcode printer for Java Control to generate, create QR image in Java applications.
www.OnBarcode.com
QR-Code Encoder In VS .NET
Using Barcode printer for ASP.NET Control to generate, create QR Code 2d barcode image in ASP.NET applications.
www.OnBarcode.com
To allow bidirectional navigation of the association, you require two attributes. The parentCategory field implements the single-valued end of the association and is declared to be of type Category. The many-valued end, implemented by the childCategories field, must be of collection type. You choose a Set, because duplicates are disallowed, and initialize the instance variable to a new instance of HashSet. Hibernate requires interfaces for collection-typed attributes, so you must use java.util.Set or java.util.List rather than HashSet, for example. This is consistent with the requirements of the JPA specification for collections in entities. At runtime, Hibernate wraps the HashSet instance with an instance of one of Hibernate s own classes. (This special class isn t visible to the application code.) It s
Making Barcode In None
Using Barcode drawer for Font Control to generate, create Barcode image in Font applications.
www.OnBarcode.com
UCC - 12 Generator In Visual Basic .NET
Using Barcode generator for Visual Studio .NET Control to generate, create UPC A image in .NET applications.
www.OnBarcode.com
Implementing the domain model
Code 39 Decoder In Java
Using Barcode scanner for Java Control to read, scan read, scan image in Java applications.
www.OnBarcode.com
Generate UCC - 12 In Objective-C
Using Barcode creator for iPad Control to generate, create UCC-128 image in iPad applications.
www.OnBarcode.com
good practice to program to collection interfaces anyway, rather than concrete implementations, so this restriction shouldn t bother you. You now have some private instance variables but no public interface to allow access from business code or property management by Hibernate (if it shouldn t access the fields directly). Let s add some accessor methods to the class:
Data Matrix ECC200 Reader In None
Using Barcode decoder for Software Control to read, scan read, scan image in Software applications.
www.OnBarcode.com
Barcode Generation In Objective-C
Using Barcode printer for iPhone Control to generate, create Barcode image in iPhone applications.
www.OnBarcode.com
public String getName() { return name; } public void setName(String name) { this.name = name; } public Set getChildCategories() { return childCategories; } public void setChildCategories(Set childCategories) { this.childCategories = childCategories; } public Category getParentCategory() { return parentCategory; } public void setParentCategory(Category parentCategory) { this.parentCategory = parentCategory; }
Barcode Creator In .NET Framework
Using Barcode generator for .NET framework Control to generate, create Barcode image in .NET framework applications.
www.OnBarcode.com
Matrix Barcode Creator In VB.NET
Using Barcode printer for .NET framework Control to generate, create 2D Barcode image in .NET framework applications.
www.OnBarcode.com
Again, these accessor methods need to be declared public only if they re part of the external interface of the persistent class used by the application logic to create a relationship between two objects. However, managing the link between two Category instances is more difficult than setting a foreign key value in a database field. In our experience, developers are often unaware of this complication that arises from a network object model with bidirectional references. Let s walk through the issue step by step. The basic procedure for adding a child Category to a parent Category looks like this:
DataMatrix Scanner In VB.NET
Using Barcode reader for Visual Studio .NET Control to read, scan read, scan image in .NET framework applications.
www.OnBarcode.com
PDF417 Creator In None
Using Barcode drawer for Font Control to generate, create PDF-417 2d barcode image in Font applications.
www.OnBarcode.com
Category aParent = new Category(); Category aChild = new Category(); aChild.setParentCategory(aParent); aParent.getChildCategories().add(aChild);
Whenever a link is created between a parent Category and a child Category, two actions are required:
Domain models and metadata
The parentCategory of the child must be set, effectively breaking the association between the child and its old parent (there can only be one parent for any child). The child must be added to the childCategories collection of the new parent Category.
Managed relationships in Hibernate Hibernate doesn t manage persistent associations. If you want to manipulate an association, you must write exactly the same code you would write without Hibernate. If an association is bidirectional, both sides of the relationship must be considered. Programming models like EJB 2.1 entity beans muddled this behavior by introducing container-managed relationships the container automatically changes the other side of a relationship if one side is modified by the application. This is one of the reasons why code that uses EJB 2.1 entity beans couldn t be reused outside the container. EJB 3.0 entity associations are transparent, just like in Hibernate. If you ever have problems understanding the behavior of associations in Hibernate, just ask yourself, What would I do without Hibernate Hibernate doesn t change the regular Java semantics.
Copyright © OnBarcode.com . All rights reserved.