how to generate barcode in vb.net 2008 Using the query API and JPQL to retrieve entities in Java

Print DataMatrix in Java Using the query API and JPQL to retrieve entities

Using the query API and JPQL to retrieve entities
Generate ECC200 In Java
Using Barcode printer for Java Control to generate, create ECC200 image in Java applications.
www.OnBarcode.com
Decode Data Matrix 2d Barcode In Java
Using Barcode recognizer for Java Control to read, scan read, scan image in Java applications.
www.OnBarcode.com
NOTE
Draw Universal Product Code Version A In Java
Using Barcode creation for Java Control to generate, create UPC Symbol image in Java applications.
www.OnBarcode.com
Linear 1D Barcode Printer In Java
Using Barcode creation for Java Control to generate, create Linear 1D Barcode image in Java applications.
www.OnBarcode.com
Always double-check the positions of parameters when using numbered parameters. If you have trouble with your queries using positional parameters, probably one or more of the positions are incorrect, which nearly always forces a data type mismatch. For this reason, we recommend that you use named parameters instead of positional parameters when possible.
Barcode Drawer In Java
Using Barcode generator for Java Control to generate, create Barcode image in Java applications.
www.OnBarcode.com
Generate Code 128 In Java
Using Barcode drawer for Java Control to generate, create Code 128 Code Set C image in Java applications.
www.OnBarcode.com
When you specify a specific name for a parameter, it s called a named parameter. Named parameters improve the readability of code tremendously and make troubleshooting your queries much easier. The previous query can be written using named parameters as follows:
Encoding Barcode In Java
Using Barcode generator for Java Control to generate, create Barcode image in Java applications.
www.OnBarcode.com
Draw Leitcode In Java
Using Barcode generator for Java Control to generate, create Leitcode image in Java applications.
www.OnBarcode.com
SELECT i FROM Item i WHERE i.initialPrice = :price
Encoding ECC200 In Java
Using Barcode creator for BIRT Control to generate, create Data Matrix ECC200 image in Eclipse BIRT applications.
www.OnBarcode.com
ECC200 Decoder In Visual C#
Using Barcode reader for Visual Studio .NET Control to read, scan read, scan image in Visual Studio .NET applications.
www.OnBarcode.com
As you can see, the only difference between the positional parameter and the named parameter is the notation of the parameter itself. A positional parameter starts with a followed by the parameter s position. A named parameter starts with : and is followed by the name of the parameter. To populate a named parameter, you have to pass the name of the parameter when calling the setParameter method on the query like this:
Code 128 Code Set C Recognizer In Java
Using Barcode scanner for Java Control to read, scan read, scan image in Java applications.
www.OnBarcode.com
UPC - 13 Recognizer In None
Using Barcode reader for Software Control to read, scan read, scan image in Software applications.
www.OnBarcode.com
query.setParameter("price", 100.00);
Recognizing Barcode In None
Using Barcode reader for Software Control to read, scan read, scan image in Software applications.
www.OnBarcode.com
Barcode Printer In Java
Using Barcode generator for BIRT reports Control to generate, create Barcode image in Eclipse BIRT applications.
www.OnBarcode.com
This code sets the named price parameter to a value of 100.00. It also makes the developer s intent a little clearer to those reading the code. Retrieving a single entity You can retrieve a single entity instance by using the Query.getSingleResult method. Be sure that the query retrieves only one entity when using this method. For example, if we are absolutely sure that no two categories in the ActionBazaar application have exactly the same name and we are retrieving an instance of the Category by its name, we can retrieve it by using
Code128 Generator In Visual Studio .NET
Using Barcode generator for ASP.NET Control to generate, create USS Code 128 image in ASP.NET applications.
www.OnBarcode.com
Generate QR Code ISO/IEC18004 In None
Using Barcode generator for Microsoft Excel Control to generate, create QR Code 2d barcode image in Excel applications.
www.OnBarcode.com
query.setParameter(1, "Recycle from Mr. Dumpster"); Category cat = (Category)query.getSingleResult();
Barcode Printer In Java
Using Barcode maker for Eclipse BIRT Control to generate, create Barcode image in Eclipse BIRT applications.
www.OnBarcode.com
Code 3 Of 9 Recognizer In Visual C#.NET
Using Barcode decoder for .NET framework Control to read, scan read, scan image in .NET framework applications.
www.OnBarcode.com
NOTE
QR Code JIS X 0510 Maker In None
Using Barcode drawer for Online Control to generate, create Denso QR Bar Code image in Online applications.
www.OnBarcode.com
Draw UPC-A In Objective-C
Using Barcode drawer for iPad Control to generate, create UPC-A Supplement 5 image in iPad applications.
www.OnBarcode.com
If your query retrieves multiple instances of Category entities with the same name, it will throw NonUniqueResultException. The persistence provider will throw NoResultException when your query does not retrieve any result.
These exceptions will not roll back the active transactions. You must handle these exceptions as follows:
Executing the queries
try { ... query.setParameter(1, "Recycle from Mr. Dumpster"); Category cat = (Category)query.getSingleResult(); ... }catch (NonUniqueResultException ex) { handleException(ex); } catch (NoResultException ex) { handleException(ex); }
Retrieving an entity using getSingleResult does not require an active transaction. However, if no transactions are available, the retrieved entity will be detached after retrieval. It s worth mentioning that the persistence provider will throw IllegalStateException if Query contains an UPDATE or DELETE statement. Retrieving a collection of entities Most queries normally retrieve more than one instance of an entity in what is commonly called a result set or result list. You can use the getResultList method of the Query interface to retrieve the results of a query. For example, to retrieve all instances of Item with an initial price between 100 and 200 using named parameters, use the following:
query.setParameter("lowPrice", lowPriceValue) query.setParameter("highPrice", highPriceValue) List items = query.getResultList();
NOTE
If getResultList does not retrieve any results for a query, it returns an empty list. No exceptions are thrown.
Here you see that lowPrice is the name parameter for the lower range parameter, and the value is provided by lowPriceValue. The upper range parameter is named highPrice in the query, and its value is specified by highPriceValue. The query.getResultsList method returns the list of items that fall within this range. As with retrieving a single entity, retrieving a collection does not require an active transaction, and if one isn t available, the retrieved entities will be detached after retrieval. Paginating through a result list A query may retrieve hundreds, or even millions of entities, and processing a retrieved list of entities is not necessarily straightforward. Here s a common way to iterate through a list of items:
Using the query API and JPQL to retrieve entities
Iterator l = items.iterator(); while (l.hasNext()) { Item item = (Item)l.next(); System.out.println("Id:" + item.getItemId() + " Initial Price:"+item.getInitialPrice()); }
This code does not provide any logic to paginate through a specific set of results. But suppose you need to create a report in which every page is limited to a display of 50 entities, and when the user clicks the Next button, the succeeding 50 entities are displayed. If you used the previous method, you d have two issues. First, the code would be more complicated than necessary to handle the 50-item page requirement. Second, you d retrieve all entities from the database at one time, which might consume a lot of memory depending on how many items were returned. The good news is that JPA provides the ability to paginate through the result set. You can use the following code to specify the pagination property for a query:
query.setMaxResults(50); query.setFirstResult(0); List items = query.getResultList();
The setMaxResults method lets you specify the maximum number of entities being retrieved in the result list, and setFirstResult lets you set the position of the first result in the ResultList. The previous code returns the first 50 entities retrieved by the query. If you want to retrieve the next 50 entities, use the following:
query.setMaxResults(50); query.setFirstResult(50); List items = query.getResultList();
The only difference between the previous two code snippets is the starting offset of the result list. Instead of hard-coding the offset and page size, you can create a method that takes these settings as a parameter:
public List getPagedItems(int pageIndex, int pageSize) { ... query.setMaxResults(pageSize) ; query.setFirstResult(pageIndex) ; return query.getResultList(); }
You can use this method from your application code to paginate through the entities. This is starting to look familiar, isn t it Now let s turn our attention to another topic: controlling the flush mode of the query.
Copyright © OnBarcode.com . All rights reserved.