how to generate barcode in vb.net 2008 Introducing the query API in Java

Maker Data Matrix in Java Introducing the query API

Introducing the query API
Create ECC200 In Java
Using Barcode creation for Java Control to generate, create ECC200 image in Java applications.
www.OnBarcode.com
Scan DataMatrix In Java
Using Barcode recognizer for Java Control to read, scan read, scan image in Java applications.
www.OnBarcode.com
Table 10.1 Comparing a JDBC basic query to a JPA query. The JDBC SQL query returns the data in the database table whereas the JPQL query returns JPA entities. Basic Steps for JDBC Query Using SQL 1. Obtain a database connection. 2. Create a query statement. 3. Execute the statement. 4. Retrieve the results (database records). Basic Steps for a JPA Query Using JPQL 1. Obtain an instance of an entity manager. 2. Create a query instance. 3. Execute the query. 4. Retrieve the results (entities).
GS1-128 Generator In Java
Using Barcode creation for Java Control to generate, create EAN / UCC - 13 image in Java applications.
www.OnBarcode.com
Code 128 Code Set C Encoder In Java
Using Barcode maker for Java Control to generate, create Code 128B image in Java applications.
www.OnBarcode.com
By now, you must be eager to see what a query looks like. Let s do that next.
2D Barcode Creator In Java
Using Barcode encoder for Java Control to generate, create Matrix Barcode image in Java applications.
www.OnBarcode.com
Making UPC - 13 In Java
Using Barcode maker for Java Control to generate, create EAN-13 image in Java applications.
www.OnBarcode.com
10.1.2 Anatomy of a query
Creating QR Code ISO/IEC18004 In Java
Using Barcode printer for Java Control to generate, create QR Code 2d barcode image in Java applications.
www.OnBarcode.com
OneCode Creator In Java
Using Barcode generator for Java Control to generate, create OneCode image in Java applications.
www.OnBarcode.com
The query API supports two types of queries: named and dynamic. Named and dynamic queries have different purposes. Named queries are intended to be stored and reused. For instance, suppose your application requires you to list the most popular item in a specific category. Since this requirement occurs in several places in your application, you know this query will be executed by multiple modules. You d probably want to create a named query so you wouldn t have to build the query every time you wanted to query the most popular item in that category. On the other hand, say you have a requirement to build a query screen for items and you want to dynamically create the query statement based on user inputs or some conditions in your application logic. In this case, you d have to use a dynamic query. Dynamic (or ad hoc) queries are different from named queries in that they are created on the fly. In either case, the format of the queries is similar. For a first taste of how a query works, let s look at an example, starting with a dynamic query. Suppose we want to retrieve all the categories in the system. The following code will perform the desired task:
Encode ECC200 In None
Using Barcode maker for Office Word Control to generate, create Data Matrix 2d barcode image in Office Word applications.
www.OnBarcode.com
Create Data Matrix 2d Barcode In None
Using Barcode generator for Font Control to generate, create Data Matrix image in Font applications.
www.OnBarcode.com
@PersistenceContext em; Injects EntityManager Creates query ... instance public List findAllCategories() { Query query = em.createQuery("SELECT c FROM Category c"); ... return query.getResultList(); ............ }
Draw Universal Product Code Version A In None
Using Barcode generator for Software Control to generate, create GTIN - 12 image in Software applications.
www.OnBarcode.com
European Article Number 13 Printer In Visual Basic .NET
Using Barcode generator for .NET Control to generate, create EAN 13 image in .NET framework applications.
www.OnBarcode.com
Retrieves result
Barcode Generator In Objective-C
Using Barcode printer for iPhone Control to generate, create Barcode image in iPhone applications.
www.OnBarcode.com
Barcode Drawer In Visual Studio .NET
Using Barcode creator for Reporting Service Control to generate, create Barcode image in Reporting Service applications.
www.OnBarcode.com
In this example, we first grab an instance of an EntityManager provided by dependency injection b. Then we create an instance of a Query object for querying entities using the EntityManager.createQuery method C, passing it the query
Creating Barcode In None
Using Barcode generation for Software Control to generate, create Barcode image in Software applications.
www.OnBarcode.com
Scan QR-Code In C#.NET
Using Barcode recognizer for .NET Control to read, scan read, scan image in .NET framework applications.
www.OnBarcode.com
Using the query API and JPQL to retrieve entities
Encode UPCA In Java
Using Barcode creation for BIRT Control to generate, create Universal Product Code version A image in BIRT reports applications.
www.OnBarcode.com
Generate GTIN - 12 In None
Using Barcode generator for Online Control to generate, create UPC-A Supplement 5 image in Online applications.
www.OnBarcode.com
string. (In section 10.2 we discuss the Query interface in more detail.) Once we have a query instance, the final step is to return the results list D using its getResultList method. Note that in this example we used JPQL to query the entities. You can use either JPQL or native SQL in both named and dynamic queries. A named query will be almost the same: the only difference is that it uses createNamedQuery rather than createQuery, and you must pass it a query object that has already been created rather than a query string. In the next section, you ll learn how to create that object for JPQL queries. We ll discuss creating the named query object for SQL queries in section 10.4.
Barcode Recognizer In .NET Framework
Using Barcode scanner for .NET Control to read, scan read, scan image in VS .NET applications.
www.OnBarcode.com
GTIN - 12 Generator In None
Using Barcode creator for Font Control to generate, create UCC - 12 image in Font applications.
www.OnBarcode.com
10.1.3 Defining named queries
You must create a named (or static) query before you can use it. It is defined either in the entity using annotations, or in the XML file defining O/R mapping metadata. You ll learn about O/R mapping and how to define a named query with XML in chapter 11. A named query is accessed by its name when you create an instance of it. Any query that is used in multiple components of your applications is a candidate for a named query. Named queries have three primary benefits:
They improve reusability of queries. They improve maintainability of code; queries are not scattered among the business logic. They can enhance performance because they are prepared once and can be efficiently reused.
Although a named query can also be stored in the ORM XML file, in this chapter we focus on using it with metadata annotations. Let s look at an example. Say you want to create a named query on the Category entity to retrieve all categories by passing a category name. To achieve this, use the @javax.persistence.NamedQuery annotation:
@Entity @NamedQuery( name = "findAllCategories", query = "SELECT c FROM Category c WHERE c.categoryName LIKE :categoryName ") public class Category implements Serializable { .. }
Copyright © OnBarcode.com . All rights reserved.