android java qr code generator The complete Hibernate mapping catalog in Java

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APPENDIX
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The complete Hibernate mapping catalog
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public class Location implements Serializable{ private Set events = new LinkedHashSet(); /** * @hibernate.set * @hibernate.collection-key column="location_id" * @hibernate.collection-one-to-many class="com.manning.hq.apdxA.Event" * @return */ public Set getEvents() { return events; } public void setEvents(Set events) { this.events = events; } }
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The desired mapping files (which the above XDoclet would generate) should be similar to this:
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<class name="com.manning.hq.apdxA.Location" table="locations"> <set name="events"> <key column="location_id"/> <one-to-many class="com.manning.hq.apdxA.Event"/> </set> </class>
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A.3 One-to-one
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The one-to-one association (see figure A.3) is not as common as its similar many-to-one cousin, mainly because database semantics don t truly allow for it. There are two strategies: identical primary keys or unique foreign keys. (A foreign key always implies a many-to-one from at least one end.) These relationships need to be bidirectional to maintain the identical keys.
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A.3.1 Identical primary keys
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Here the relationship uses a special foreign key generation algorithm:
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One-to-one
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Event
KeyNoteSpeaker
Figure A.3 One-to-one relationship: Event to KeyNoteSpeaker
/** @hibernate.class table="keynote_speakers" */ public class KeyNoteSpeaker implements Serializable { private Long id; private Event event; /** * @hibernate.id generator-class="foreign" * @hibernate.generator-param name="property" value="event" */ public Long getId() { return id; } public void setId(Long id) { this.id = id; } /** * @hibernate.one-to-one constrained="true" */ public Event getEvent() { return event; } public void setEvent(Event event) { this.event = event; } } /** @hibernate.class table="events" */ public class Event implements Serializable { private KeyNoteSpeaker speaker; /** @hibernate.one-to-one */ public KeyNoteSpeaker getSpeaker() { return speaker; } public void setSpeaker(KeyNoteSpeaker speaker) { this.speaker = speaker; } }
In the following code, KeyNoteSpeaker is the child class whose id is dependent on (and identical to) the parent Event:
APPENDIX
The complete Hibernate mapping catalog
<class name="com.manning.hq.apdxA.KeyNoteSpeaker" table="keynote_speakers"> <id name="id" column="id" type="java.lang.Long"> <generator class="foreign"> <param name="property">event</param> </generator> </id> <one-to-one name="event" class="com.manning.hq.apdxA.Event" constrained="true" /> </class> <class name="com.manning.hq.apdxA.Event" table="events"> <one-to-one name="speaker" class="com.manning.hq.apdxA.KeyNoteSpeaker" constrained="false" /> </class>
Table schema
Since events.id and keynote_speakers.id must match, there is no need for a foreign key. This works well in many cases, except when you re using native key generation, which means the database is managing the key generation and foreign key violations become possible. In that case, you can try to use the next one-to-one strategy.
events id keynote_speakers id
A.3.2 Foreign key one-to-one
The foreign key one-to-one is really a constrained many-to-one relationship, where one object is a many-to-one relationship to the other, using a unique foreign key to the other object. Unlike the primary key one-to-one, it can but does not need to be bidirectional.
Unidirectional
The following shows an Event with a foreign one-to-one relationship:
One-to-one
public class Event implements Serializable { private KeyNoteSpeaker speaker; /** * @hibernate.many-to-one column="keynote_speaker_id" * unique="true" */ public KeyNoteSpeaker getSpeaker() { return speaker; } public void setSpeaker(KeyNoteSpeaker speaker) { this.speaker = speaker; } }
Because the keynote_speaker_id is unique, no other event can be associated with a single KeyNoteSpeaker. Here s the mapping file for this relationship:
<class name="com.manning.hq.apdxA.Event" table="events"> <many-to-one name="keyNoteSpeaker" class="com.manning.hq.apdxA.KeyNoteSpeaker" column="keynote_speaker_id" unique="true" /> </class>
Note that as of XDoclet 1.2.3, a bug results in the generation of multiple unique="true" attributes. Until it s fixed, you can just ignore that attribute or handwrite the mapping file.
Table schema
Since there is now a foreign key link, a new column must be added to the events table.
events id keynote_speaker_id keynote_speakers id
APPENDIX
The complete Hibernate mapping catalog
Bidirectional
The Event-to-KeyNoteSpeaker association can be made bidirectional by adding an event field to KeyNoteSpeaker and mapping it to point back to Event s keyNoteSpeaker field:
public class KeyNoteSpeaker implements Serializable { private Long id; private Event event; /** * @hibernate.id generator-class="native" */ public Long getId() { return id; } public void setId(Long id) { this.id = id; } /** * @hibernate.one-to-one property-ref="keyNoteSpeaker" */ public Event getEvent() { return event; } public void setEvent(Event event) { this.event = event; } }
Note that KeyNoteSpeaker can also use a normal id generator now instead of the foreign one that we saw before. The newly generated KeyNoteSpeaker.hbm.xml file will contain the following:
<class name="com.manning.hq.apdxA.KeyNoteSpeaker" table="keynote_speakers"> <id name="id" column="id" type="java.lang.Long"> <generator class="native"/> </id> <one-to-one name="event" class="com.manning.hq.apdxA.Event" constrained="false" property-ref="keyNoteSpeaker" /> </class>
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