generate barcode in asp.net c# Querying with HQL and JPA QL in Java

Drawer Quick Response Code in Java Querying with HQL and JPA QL

The EJB container will acknowledge the message if the onMessage() method returns successfully. If, however, a RuntimeException is thrown by the onMessage() method, the container will not acknowledge the message, and the JMS provider will suspect a problem and probably attempt to redeliver the message. If redelivery of a message is important when a transaction fails, your best course of action is to ensure that the onMessage() method throws an EJBException so that the container will not acknowledge the message received from the JMS provider.

In this code, the use of UPDATE and DELETE statements is quite similar to using any other JPQL statements, except for two significant differences. First, we use the executeUpdate method of the Query interface to perform bulk updates and deletes instead of getResultList or getSingleResult. Second, we must invoke executeUpdate within an active transaction. Because bulk updates and deletes involve many pitfalls, we recommend that you isolate any bulk operations to a discrete transaction, because they are directly translated into database operations and may cause inconsistencies between managed entities and the database. Vendors are only required to execute the update or delete operations, and not required to modify any changes to the managed entities according the specification. In other words, the persistence provider won t remove any associated entities when an entity is removed as a result of a bulk operation. At this point, we ve covered a lot of ground: queries, annotations, and JPQL. There s only one topic left to discuss in this arena: using regular SQL queries in EJB 3.

That s it for the data access layer, and I hope that you have appreciated how simple these methods are just a single line of code is all that is required to run statements against our DataLayer and obtain results. All of our hard work has been worthwhile! While creating our data access code we ve seen some interesting new .NET 2.0 features. These were

SELECT scans a table (LineItems), looking for all records matching a given criterion (RecordID = 92231), and returns a smaller table that contains just the indicated fields (ProductID and Quantity) for the matching records. The most basic query returns all rows and columns.

Domain constraint A domain is (loosely speaking, and in the database world) a datatype in a database. Hence, a domain constraint defines the range of possible values a particular datatype can handle. For example, an int datatype is usable for integer values. A char datatype can hold character strings: for example, all characters defined in ASCII. Because we mostly use datatypes that are built in to the database management system, we rely on the domain constraints as defined by the vendor. If you create user-defined datatypes (UDT), you ll have to define their constraints. If they re supported by your SQL database, you can use the (limited) support for custom domains to add additional constraints for particular datatypes. Column constraint Restricting a column to hold values of a particular domain is equivalent to adding a column constraint. For example, you declare in DDL that the INITIAL_PRICE column holds values of the domain MONEY, which internally uses the datatype number(10,2). You use the datatype directly most of the time, without defining a domain first. A special column constraint in an SQL database is NOT NULL. Table constraint An integrity rule that applies to a single row or several rows is a table constraint. A typical declarative table constraints is UNIQUE (all rows are checked for duplicate values). A sample rule affecting only a single row is end date of an auction must be later than the start date. Database constraint If a rule applies to more than one table, it has database scope. You should already be familiar with the most common database constraint, the foreign key. This rule guarantees the integrity of references between rows, usually in separate tables, but not always (self-referencing foreign key constraints aren t uncommon).

Dog might have properties called color and size, for example. Each object might have different values for each property, but by definition they all must have the property. So Sparky might have a color of brown and a size of large, whereas Frisky has a color of white and a size of small, but they re both still members of Dog. In ASP.NET, a Label control has properties for Text and Font.

Now run the application again, and try entering random data in the text box. You ll see that numbers, even zero or negative numbers, pass validation, while anything else fails. You can imagine how this sort of validation would be useful for order numbers, credit card numbers, or anyplace where the type of data is important.

does not differentiate between JPQL and native SQL, and the same interface can be used for both types of queries. Table 10.3 lists all methods of the Query interface. You can use these methods on the query instance for setting parameters for the query or for executing the query or iterating through the results after you retrieve them. Here is a quick example of some commonly used Query methods in action:

You have an idea how the BLOB storage service is hosted in Windows Azure. Let s look at how files are stored in the service. In this section, we ll look at the three layers of BLOB storage: The account The container The BLOB

Figure 1.3 This book s webpage as shown in Mobile Safari on the iPad. The simplified navigation maximizes the usable viewing area.

tag mapping 261 target attribute 388 389, 397, 401 control 308 property 359 targetControl parameter 311 TargetControlID property 317, 336, 339, 355, 360 TargetControlType attribute 316, 352 Temperature class 100 template cloning 474 declaring for drag visual 478 empty 473, 481 item 473 layout 473 supported by ListView 473 text box 49 auto-complete 334 340 enhancing 282 text field limiting input 49

To give you a sneak preview, figure 8.1 shows what your page will look like. As you see, the current month s events are displayed in a table-based calendar. Back and Next links allow users to go back and forth among the months. Note that the URL is from the WebWork application, but the basic display will be the same for all of the applications.