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data matrix barcode generator java Object-relational mapping in Java
Object-relational mapping Draw Data Matrix 2d Barcode In Java Using Barcode generation for Java Control to generate, create Data Matrix 2d barcode image in Java applications. www.OnBarcode.comScanning Data Matrix In Java Using Barcode decoder for Java Control to read, scan read, scan image in Java applications. www.OnBarcode.com@Id @GeneratedValue(strategy=GenerationType.TABLE, generator="USER_TABLE_GENERATOR") @Column(name="USER_ID") protected Long userId; Create PDF-417 2d Barcode In Java Using Barcode creator for Java Control to generate, create PDF417 image in Java applications. www.OnBarcode.comUPC Symbol Printer In Java Using Barcode encoder for Java Control to generate, create GS1 - 12 image in Java applications. www.OnBarcode.comDefault primary key generation strategy The last option for key generation is to let the provider decide the best strategy for the underlying database by using the AUTO specification as follows: Draw ECC200 In Java Using Barcode drawer for Java Control to generate, create Data Matrix 2d barcode image in Java applications. www.OnBarcode.comEncoding Code-128 In Java Using Barcode creation for Java Control to generate, create ANSI/AIM Code 128 image in Java applications. www.OnBarcode.com@Id @GeneratedValue(strategy=GenerationType.AUTO) @Column(name="USER_ID") protected Long userId; Printing UPC Code In Java Using Barcode creator for Java Control to generate, create UCC - 12 image in Java applications. www.OnBarcode.comCreating UPC - E0 In Java Using Barcode printer for Java Control to generate, create UPC-E Supplement 2 image in Java applications. www.OnBarcode.comThis is a perfect match for automatic table creation because the underlying database objects required will be created by the JPA provider. Data Matrix 2d Barcode Drawer In VB.NET Using Barcode creator for .NET Control to generate, create Data Matrix 2d barcode image in .NET applications. www.OnBarcode.comGenerate Data Matrix ECC200 In Java Using Barcode drawer for Java Control to generate, create Data Matrix image in Java applications. www.OnBarcode.comNOTE
QR Code JIS X 0510 Maker In Java Using Barcode generation for BIRT reports Control to generate, create QR Code image in BIRT applications. www.OnBarcode.comPrinting PDF-417 2d Barcode In VB.NET Using Barcode drawer for .NET framework Control to generate, create PDF 417 image in .NET applications. www.OnBarcode.comYou d assume that if Oracle were the underlying database, the persistence provider probably would choose SEQUENCE as the strategy; if SQL Server were the underlying database, IDENTITY would likely be chosen on your behalf. However, this may not be true, and we recommend that you check the documentation of your persistence provider. For example, TopLink Essentials uses a table generator as the default autogenerator for all databases. Decoding Barcode In Visual Studio .NET Using Barcode Control SDK for ASP.NET Control to generate, create, read, scan barcode image in ASP.NET applications. www.OnBarcode.comBarcode Scanner In Visual C#.NET Using Barcode recognizer for VS .NET Control to read, scan read, scan image in .NET applications. www.OnBarcode.comKeep in mind that although generated values are often used for surrogate keys, you could use the feature for any persistence field or property. Before we move on to discussing entity relations, we ll tackle the most complicated case of mapping basic entity data next mapping embeddable objects. PDF-417 2d Barcode Maker In None Using Barcode drawer for Office Word Control to generate, create PDF417 image in Word applications. www.OnBarcode.comCode-39 Creator In None Using Barcode drawer for Microsoft Excel Control to generate, create Code 39 Full ASCII image in Office Excel applications. www.OnBarcode.comStandardization of key generation
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When discussing embeddable objects in chapter 7, we explained that an embeddable object acts primarily as a convenient data holder for entities and has no Mapping entities
Figure 8.3 Embeddable objects act as convenient data holders for entities and have no identity of their own. Address is an embeddable object that is stored as a part of the User entity that is mapped to the USERS table. identity of its own. Rather, it shares the identity of the entity class it belongs to. Let s now discuss how embeddable objects are mapped to the database (figure 8.3). In listing 8.4, we included the Address embedded object introduced in chapter 7 in the User entity as a data field. The relevant parts of listing 8.4 are repeated in listing 8.6 for easy reference. Listing 8.6 Using embeddable objects
@Table(name="USERS") Table stores both entity and embeddable object ... public class User implements Serializable { Shared identity
@Id @Column(name="USER_ID", nullable=false) protected Long userId; ... Embedded field @Embedded protected Address address; ... } ... Object-relational mapping
@Embeddable public class Address implements Serializable { @Column(name="STREET", nullable=false) protected String street; ... @Column(name="ZIP_CODE", nullable=false) protected String zipCode; ... } Embeddable object
Embeddable object field mappings
The User entity defines the address field as an embedded object D. Notice that unlike the User entity, the embeddable Address object E is missing an @Table annotation. This is because EJB 3 does not allow embedded objects to be mapped to a table different from the enclosing entity, at least not directly through the @Table annotation. Instead, the Address object s data is stored in the USERS table that stores the enclosing entity b. Therefore, the @Column mappings applied to the fields of the Address object F really refer to the columns in the USERS table. For example, the street field is mapped to the USERS.STREET column, the zipCode field is mapped to the USERS.ZIP_CODE column, and so on. This also means that the Address data is stored in the same database row as the User data, and both objects share the USER_ID identity column C. Other than this minor nuance, all data mapping annotations used in entities are available for you in embedded objects and behave in exactly the same manner. In general, this is the norm and embedded objects are often stored in the same table as the enclosing entity. However, if this does not suit you, it is possible to store the embeddable object s data in a separate table and use the @SecondaryTable annotation to retrieve its data into the main entity using a join. We won t detail this solution, as it is fairly easy to figure out and we ll leave it for you to experiment with instead.
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