barcode font vb.net Implementing domain objects with JPA in Java

Creator Data Matrix 2d barcode in Java Implementing domain objects with JPA

Implementing domain objects with JPA
Data Matrix 2d Barcode Creation In Java
Using Barcode creator for Java Control to generate, create Data Matrix 2d barcode image in Java applications.
www.OnBarcode.com
Scanning DataMatrix In Java
Using Barcode decoder for Java Control to read, scan read, scan image in Java applications.
www.OnBarcode.com
We ll discuss the @Embeddable annotation after we discuss entity identities. For now, think of an embeddable object as a custom data type for an entity that encapsulates persisted data. We have already touched on the issue of identity when we talked about uniquely identifying the Category domain object through the id property. Let s now take up the topic of entity identity in greater detail.
Make Barcode In Java
Using Barcode creator for Java Control to generate, create Barcode image in Java applications.
www.OnBarcode.com
Painting DataMatrix In Java
Using Barcode printer for Java Control to generate, create Data Matrix image in Java applications.
www.OnBarcode.com
7.2.3 Specifying entity identity Every entity of the domain model must be uniquely identifiable. This requirement is due partly to the fact that at some point entities must be persisted into a uniquely identifiable row in a database table (or set of rows in multiple tables). If you are familiar with the concept of database table primary keys, this should come as no surprise. Without primary keys, you would never be able to uniquely identify and retrieve the data you put into a record since you would not know which row it went into after performing the save! The concept of being able to distinguish different instances of the same object holding a different set of data is not completely alien to object-oriented programming either. Consider the equals method in java.lang.Object, meant to be overridden by subclasses as necessary. This method is the OO equivalent of comparing the primary keys of two distinct database records. In most cases, the equals method is implemented by comparing the data that uniquely identifies instances of the same object from one another. In the case of the Category object, you might imagine that the equals method would look like this:
Paint Code 3 Of 9 In Java
Using Barcode printer for Java Control to generate, create Code 39 Extended image in Java applications.
www.OnBarcode.com
Draw GS1 - 12 In Java
Using Barcode creator for Java Control to generate, create UPC Symbol image in Java applications.
www.OnBarcode.com
public boolean equals (Object other) { if (other instanceof Category) { return this.name.equals(((Category)other).name) } else { return false; } }
Make QR Code In Java
Using Barcode generator for Java Control to generate, create QR Code image in Java applications.
www.OnBarcode.com
Universal Product Code Version E Maker In Java
Using Barcode encoder for Java Control to generate, create UPCE image in Java applications.
www.OnBarcode.com
In this case, we would be assuming that the name instance variable uniquely identifies a Category. The name field therefore is the identity for the Category object. In listing 7.1, however, we choose the id field as the identity for Category. This choice will be more obvious when we talk about mapping the Category object into a database table. As you ll see, in effect, we choose this instance variable because we get it free from the database as a unique Category identifier, and it is less resource intensive than comparing the java.lang.String name field since it is a numeric java. lang.Long. Another benefit of using the numeric type key is automatic generation. There are several ways of telling the persistence provider where
Drawing Data Matrix ECC200 In Java
Using Barcode generator for Android Control to generate, create Data Matrix ECC200 image in Android applications.
www.OnBarcode.com
Scanning Data Matrix 2d Barcode In Java
Using Barcode reader for Java Control to read, scan read, scan image in Java applications.
www.OnBarcode.com
Implementing domain models
Data Matrix ECC200 Generation In VB.NET
Using Barcode generation for .NET framework Control to generate, create Data Matrix 2d barcode image in .NET framework applications.
www.OnBarcode.com
Barcode Creation In None
Using Barcode creator for Microsoft Excel Control to generate, create Barcode image in Microsoft Excel applications.
www.OnBarcode.com
the identity of an entity is stored. Starting with the simplest and ending with the most complex, these are as follows:
Barcode Drawer In None
Using Barcode creation for Font Control to generate, create Barcode image in Font applications.
www.OnBarcode.com
Decode GS1 - 13 In .NET
Using Barcode reader for Visual Studio .NET Control to read, scan read, scan image in Visual Studio .NET applications.
www.OnBarcode.com
Using the @Id annotation Using the @IdClass annotation Using the @EmbeddedId annotation
QR Code ISO/IEC18004 Generator In None
Using Barcode printer for Software Control to generate, create QR-Code image in Software applications.
www.OnBarcode.com
UPC Symbol Encoder In VS .NET
Using Barcode generator for ASP.NET Control to generate, create GS1 - 12 image in ASP.NET applications.
www.OnBarcode.com
Let s look at each of these mechanisms next. The @Id annotation Using the javax.persistence.Id annotations is the simplest way of telling the persistence provider where the entity identity is stored. The @Id annotation marks a field or property as identity for an entity. Since we are using property-based persistence for the Category entity, we could let the API know that we are using the id property as the identity by applying the @Id annotation to the getId method as in the following code snippet. In the case of field-based persistence, the @Id annotation would have been applied directly to an instance variable instead.
Barcode Creator In .NET
Using Barcode creation for Visual Studio .NET Control to generate, create Barcode image in Visual Studio .NET applications.
www.OnBarcode.com
Generate DataMatrix In Objective-C
Using Barcode creation for iPhone Control to generate, create ECC200 image in iPhone applications.
www.OnBarcode.com
@Entity public class Category { ... protected Long id; ... @Id public Long getId() { return this.id; } public void setId(Long id) { this.id = id; } ... }
Barcode Recognizer In Java
Using Barcode Control SDK for Java Control to generate, create, read, scan barcode image in Java applications.
www.OnBarcode.com
Print EAN-13 In None
Using Barcode maker for Online Control to generate, create EAN-13 Supplement 5 image in Online applications.
www.OnBarcode.com
Because the identity we specify will end up in a database primary key column, there are limitations to what data types an identity might have. EJB 3 supports primitives, primitive wrappers, and Serializable types like java.lang.String, java. util.Date, and java.sql.Date as identities. In addition, when choosing numeric types you should avoid types such as float, Float, double, and so forth because of the indeterminate nature of type precision. For example, let s assume that we are using float data as the identity, and specify 103.789 and 103.787 as the identity values for two separate entity instances. If the database rounds these values to two-digit decimal precision before storing the record, both of these values would
Copyright © OnBarcode.com . All rights reserved.