how to generate barcode in vb.net 2008 Find by primary key using composite keys in Java

Generator Data Matrix ECC200 in Java Find by primary key using composite keys

Listing 9.7 Find by primary key using composite keys
Create Data Matrix 2d Barcode In Java
Using Barcode printer for Java Control to generate, create Data Matrix ECC200 image in Java applications.
www.OnBarcode.com
Data Matrix Scanner In Java
Using Barcode reader for Java Control to read, scan read, scan image in Java applications.
www.OnBarcode.com
SellerPK sellerKey = new SellerPK(); sellerKey.setFirstName(firstName); sellerKey.setLastName(lastName); Seller seller = entityManager.find(Seller.class, sellerKey);
Data Matrix 2d Barcode Generation In Java
Using Barcode drawer for Java Control to generate, create ECC200 image in Java applications.
www.OnBarcode.com
Drawing USS Code 128 In Java
Using Barcode creator for Java Control to generate, create Code 128 Code Set B image in Java applications.
www.OnBarcode.com
The find method does what it does by inspecting the details of the entity class passed in as the first parameter and generating a SELECT statement to retrieve the entity data. This generated SELECT statement is populated with the primary key values specified in the second parameter of the find method. For example, the find method in listing 9.1 could generate a SELECT statement that looks something like this:
EAN13 Generation In Java
Using Barcode creation for Java Control to generate, create EAN-13 image in Java applications.
www.OnBarcode.com
GS1 RSS Generator In Java
Using Barcode generation for Java Control to generate, create GS1 DataBar-14 image in Java applications.
www.OnBarcode.com
SELECT * FROM SELLERS WHERE seller_id = 1
Making Code 128C In Java
Using Barcode creator for Java Control to generate, create Code 128C image in Java applications.
www.OnBarcode.com
USD-3 Generator In Java
Using Barcode creation for Java Control to generate, create Code 93 image in Java applications.
www.OnBarcode.com
Note that if an entity instance matching the specified key does not exist in the database, the find method will not throw any exceptions. Instead, the EntityManager will return null or an empty entity and your application must handle this situation. It is not strictly necessary to call the find method in a transactional context. However, the retrieved entity is detached unless a transaction context is available, so it is generally advisable to call the find method inside a transaction. One of the most important features of the find method is that it utilizes EntityManager caching. If your persistence provider supports caching and the entity already exists in the cache, then the EntityManager returns a cached instance of the entity instead of retrieving it from the database. Most persistence providers like Hibernate and Oracle TopLink support caching, so you can more or less count on this extremely valuable optimization. There is one more important JPA feature geared toward application optimization lazy and eager loading. The generated SELECT statement in our example attempts to retrieve all of the entity field data when the find method is invoked. In general, this is exactly what will happen for entity retrieval since it is the default behavior for JPA. However, in some cases, this is not desirable behavior.
Drawing ECC200 In Visual Basic .NET
Using Barcode creator for Visual Studio .NET Control to generate, create ECC200 image in Visual Studio .NET applications.
www.OnBarcode.com
Data Matrix 2d Barcode Scanner In Visual Basic .NET
Using Barcode decoder for .NET Control to read, scan read, scan image in .NET framework applications.
www.OnBarcode.com
Managing persistence operations
Make GTIN - 128 In None
Using Barcode generation for Excel Control to generate, create EAN / UCC - 13 image in Office Excel applications.
www.OnBarcode.com
PDF-417 2d Barcode Scanner In Java
Using Barcode reader for Java Control to read, scan read, scan image in Java applications.
www.OnBarcode.com
Fetch modes allow us to change this behavior to optimize application performance when needed. Entity fetch modes We briefly mentioned fetch modes in previous chapters but haven t discussed them in great detail. Discussing entity retrieval is an ideal place to fully explore fetch modes. As we suggested, the EntityManager normally loads all entity instance data when an entity is retrieved from the database. In ORM-speak, this is called eager fetching, or eager loading. If you have ever dealt with application performance problems due to premature or inappropriate caching, you probably already know that eager fetching is not always a good thing. The classic example we used in previous chapters is loading large binary objects (BLOBs), such as pictures. Unless you are developing a heavily graphics-oriented program such as an online photo album, it is unlikely that loading a picture as part of an entity used in a lot of places in the application is a good idea. Because loading BLOB data typically involves long-running, I/O-heavy operations, they should be loaded cautiously and only as needed. In general, this optimization strategy is called lazy fetching. JPA has more than one mechanism to support lazy fetching. Specifying column fetch-mode using the @Basic annotation is the easiest one to understand. For example, we can set the fetch mode for the picture property on the Item entity to be lazy as follows:
Create Barcode In Visual C#
Using Barcode generator for .NET framework Control to generate, create Barcode image in .NET applications.
www.OnBarcode.com
ANSI/AIM Code 39 Maker In None
Using Barcode encoder for Software Control to generate, create USS Code 39 image in Software applications.
www.OnBarcode.com
@Column(name="PICTURE") @Lob @Basic(fetch=FetchType.LAZY) public byte[] getPicture() { return picture; }
GS1 DataBar Expanded Printer In .NET
Using Barcode generator for VS .NET Control to generate, create GS1 DataBar image in .NET applications.
www.OnBarcode.com
Drawing Barcode In VB.NET
Using Barcode maker for .NET Control to generate, create Barcode image in Visual Studio .NET applications.
www.OnBarcode.com
A SELECT statement generated by the find method to retrieve Item entities would not load data from the ITEMS.PICTURE column into the picture field. Instead, the picture data will be automatically loaded from the database when the property is first accessed through the getPicture method. Be advised, however, that lazy fetching is a double-edged sword. Specifying that a column be lazily fetched means that the EntityManager will issue an additional SELECT statement just to retrieve the picture data when the lazily loaded field is first accessed. In the extreme case, imagine what would happen if all entity data in an application is lazily loaded. This would mean that the database would be flooded with a large number of frivolous SELECT statements as entity data is accessed. Also, lazy fetching is an optional EJB 3 feature, which means not every
UCC - 12 Generator In None
Using Barcode creation for Font Control to generate, create EAN128 image in Font applications.
www.OnBarcode.com
Encoding Barcode In .NET Framework
Using Barcode generation for Reporting Service Control to generate, create Barcode image in Reporting Service applications.
www.OnBarcode.com
Data Matrix Creation In .NET Framework
Using Barcode drawer for .NET framework Control to generate, create ECC200 image in .NET applications.
www.OnBarcode.com
Printing QR Code ISO/IEC18004 In None
Using Barcode drawer for Online Control to generate, create QR Code ISO/IEC18004 image in Online applications.
www.OnBarcode.com
Copyright © OnBarcode.com . All rights reserved.