CHAPTER 6 n MAPPING WITH ANNOTATIONS 121 (Best web design) n
CHAPTER 6 n MAPPING WITH ANNOTATIONS 121 n MAPPING WITH ANNOTATIONS 121 name is the name of the discriminator column. discriminatorType is the type of value to be stored in the column as selected from the javax.persistence.DiscriminatorType enumeration of STRING, CHAR, or INTEGER. columnDefinition is a fragment of DDL defining the column type. Using this is liable to reduce the portability of your code across databases. length is the column length of STRING discriminator types. It is ignored for CHAR and INTEGER types. All of these (and the annotation itself) are optional, but we recommend supplying at least the name attribute. If no @DiscriminatorColumn is specified in the hierarchy, a default column name of DTYPE and type of STRING will be used. Hibernate will supply an appropriate discriminator value for each of your entities. For example, if the STRING discriminator type is used, the value this column contains will be the name of the entity (which defaults to the class name). You can also override this behavior with specific values using the @DiscriminatorValue annotation. If the discriminator type is INTEGER, any value provided via the @DiscriminatorValue annotation must be convertible directly into an integer. In Listing 6-22, we specify that an INTEGER discriminator type should be stored in the column named DISCRIMINATOR. Rows representing Book entities will have a value of 1 in this column, whereas the following mapping in Listing 6-23 requires that rows representing ComputerBook entities should have a value of 2 in the same column. Listing 6-22. The Root of the Inheritance Hierarchy Mapped with the SINGLE_TABLE Strategy @Entity @Inheritance(strategy = SINGLE_TABLE) @DiscriminatorColumn( name=”DISCRIMINATOR”, discriminatorType=INTEGER ) @DiscriminatorValue(”1″) public class Book { … } Listing 6-23. A Derived Entity in the Inheritance Hierarchy @Entity @DiscriminatorValue(”2″) public class ComputerBook extends Book { … } An alternative to the monolithic single table approach is the otherwise similar joined table approach. Here a discriminator column is used, but the fields of the various derived types are stored in distinct tables. Other than the differing strategy, this inheritance type is specified in the same way (as shown in Listing 6-24).
Note: If you are looking for cheap and reliable webhost to host and run your web application check Vision coldfusion web hosting services