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attributes as the @hibernate.property tag. Table 9.5 contains some of the common ones.
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Table 9.5 Common @hibernate.many-to-one attributes Attribute column class Description Contains the name of column in the database. Contains the associated persistent class. Default The name of the field. The class of the field. Usually XDoclet can guess this so it s not necessary to specify. None. Acceptable values include all, none, saveupdate, or delete. false.
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Specifies how cascading operations should be handled from parent to child. Specifies that a unique constraint should be enforced. Specifies that a not-null constraint should be enforced.
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not-null
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false.
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In most cases, only cascade and column need to be specified. As an example, let s add the many-to-one relationship between Event and Location using the @hibernate.many-to-one tag. First, add the following to the Event class:
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public class Event implements Serializable { private Location location; /** * @hibernate.many-to-one column="location_id" * cascade="save-update" */ public Location getLocation() { return location; } public void setLocation(Location location) { this.location = location; } }
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Hibernating with XDoclet
Here you see @hibernate.many-to-one in action. You ve mapped the location field to a location_id column in the events table. XDoclet will extract the correct class, in this case com.manning.hq.Location, by looking at the return type of the getLocation() method. The next step is to make sure that Location itself has a mapping file, which you can generate via XDoclet as well:
package com.manning.hq.ch09; import java.io.Serializable; /** * @hibernate.class table="locations" */ public class Location implements Serializable{ private Long id; /** * @hibernate.id generator-class="native" column="uid" */ public Long getId() { return id; } public void setId(Long id) { this.id = id; } }
There s nothing really new here; you ve just defined the Location object with an id field. Now when you run the generate-hbm task via Ant, XDoclet adds the following to the Event.hbm.xml file:
<many-to-one name="location" class="com.manning.hq.ch09.Location" cascade="save-update" outer-join="auto" update="true" insert="true" access="property" column="location_id" />
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A complete many-to-one element has been added to the Event.hbm.xml file. In addition, you may notice the previous code has a few attributes that you might not be familiar with. Check the Hibernate manual and XDoclet manuals for more information.
9.3.2 The @hibernate.component tag
The next basic relationship we want to cover involves components. As you might remember, components are not full-blown entities, like Event or Location, but are just simple value objects whose values are stored in the same table as their parent objects. XDoclet can be used to mark both the component object itself (where the field-to-column mapping must be done) and the component field on the entity object. We ll use the example from chapter 4, where our Location object had an Address component. When XDoclet parses the Java files, it will combine the information from the Address class and Location class into a single Location.hbm.xml. Remember that since Address is a component, it doesn t need its own Address.hbm.xml file.
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Generating the mapping files for a component isn t much different than what you ve seen. You add @hibernate.property tags to the fields of the component object, but you don t need to declare a @hibernate.class tag on the component. The parent class then uses the @hibernate.component tag to pull the information from the component object. It s a simple tag, with only a few attributes, as table 9.6 shows.
Table 9.6 @hibernate.component attributes Attribute class Description Default
Contains the fully-qualified The return type of the getter class name of the component. method (XDoclet can usually guess). Contains a column prefix that allows multiple components of the same type on a single entity. No prefix, which is fine when only one component exists per class.
prefix
Hibernating with XDoclet
For the simplest cases, neither attribute needs to be specified. XDoclet can usually guess the name of the class, so you don t have to include class. The prefix attribute is only used when you need multiple components of the same type. We look at this prefix in the short section that follows. Let s put the @hibernate.component tag into motion by marking up our component, the Address object (see listing 9.3). Listing 9.3 An Address component, XDoclet-style
package com.manning.hq.ch09; import java.io.Serializable; /** An Address component, it does not have its own identity public class Address implements Serializable { private String streetAddress; private String city; // Other properties omitted */
/** * @hibernate.property column="street_address" */ public String getStreetAddress() { return streetAddress; } public void setStreetAddress(String streetAddress) { this.streetAddress = streetAddress; } /** * @hibernate.property column="city" */ public String getCity() { return city; } public void setCity(String city) { this.city = city; } // Other getter/setter methods omitted }
As you can see, we have marked the properties as persistent, but there is no @hibernate.class tag that would mark it as a persistent entity. Next, add the following to the Location class you created earlier in this chapter:
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