120 CHAPTER 6 n MAPPING WITH ANNOTATIONS CHAPTER 6 n MAPPING WITH ANNOTATIONS Listing 6-20. The Author Side of the Many-to-Many Association @ManyToMany(mappedBy = “authors”) public Set getBooks() { return books; } Alternatively, we could specify the link table in full, as in Listing 6-21. Listing 6-21. Specifying the Link Table in Full Using the Book Entity Annotations @ManyToMany(cascade = ALL) @JoinTable( name=”Books_to_Author”, joinColumns={@JoinColumn(name=”book_ident”)}, inverseJoinColumns={@JoinColumn(name=”author_ident”)} ) public Set getAuthors() { return authors; } Inheritance The EJB 3 standard and Hibernate both support three approaches to mapping inheritance hierarchies into the database. These are as follows: Single table (SINGLE_TABLE) Joined (JOINED) Table-per-class (TABLE_PER_CLASS) Persistent entities that are related by inheritance must be marked up with the @Inheritance annotation. This takes a single strategy attribute, which is set to one of three javax.persistence.InheritanceType enumeration values corresponding to these approaches (shown in brackets in the preceding bulleted list). The single table approach manages one class for the superclass and all its subtypes. There are columns for each mapped field or property of the superclass, and for each distinct field or property of the derived types. When following this strategy, you will need to ensure that columns are appropriately renamed when any field or property names collide in the hierarchy. To determine the appropriate type to instantiate when retrieving entities from the database, an @DiscriminatorColumn annotation should be provided in the root (and only in the root) of the persistent hierarchy.3 This defines a column containing a value that distinguishes between each of the types used. The attributes permitted by the @DiscriminatorColumn annotation are as follows: 3. That is to say, the highest class in the hierarchy that is mapped to the database as an entity should be annotated in this way.
Note: If you are looking for best quality webspace to host and run your tomcat application check Vision tomcat hosting services
This entry was posted
on Thursday, April 26th, 2007 at 6:12 pm and is filed under tomcat.
You can follow any responses to this entry through the RSS 2.0 feed.
You can leave a response, or trackback from your own site.