Hibernate

Reference

Star.java

private Set<String> planets = new HashSet<String>();

Star.hbm.xml

<set name="planets" table="star_planet">
	<key column="star_id" />
	<element type="text"/>
</set>

Star.java

private SortedSet<String> planets = new TreeSet<String>();

Star.hbm.xml

<set name="planets" table="star_planet" sort="natural">
	<key column="star_id" />
	<element type="text"/>
</set>

Star.java

private List<String> planets = new LinkedList<String>();

Star.hbm.xml

<list name="planets" table="star_planet">
	<key column="star_id" />
	<list-index column="index" />
	<element type="text"/>
</list>

Star.java

private Map<String, String> planets = new HashMap<String, String>();

Star.hbm.xml

<map name="planets" table="star_planet">
	<key column="star_id" />
	<map-key type="text" column="planet_name" />
	<element type="text" column="planet_description"/>
</map>

Star.java

private List<Planet> planets = new LinkedList<Planet>();

Star.hbm.xml

<list name="planets" table="star_planet">
  <key column="star_id" />
  <list-index column="index" />
  <many-to-many column="planet_id" class="Planet"/>
</list>

In Eclipse:

• For each model class: Source -> Sort Members

For each model class (Toto.java):

• create the Hibernate file (Toto.hbm.xml) in the same folder as the model class

Note: when using inheritance, subclasses' Hibernate mapping can be done in their superclass' mapping file.

Declare each Hibernate file in hibernate.cfg.xml

For each model class:

• write simple attributes (String, Integer, Short, Date...) mappings in Hibernate file

For each model class:

• write collections and relationships mappings in Hibernate file

• Don't forget inter-package relationships.
• Bidirectional relationships: make sure one side has inverse=“true”

Enclose the table or column name in backticks

<class name="User" table="`user`">
</class>

Reference: http://www.hibernate.org/hib_docs/v3/reference/en/html_single/#mapping-quotedidentifiers

Then for command line SQL queries (PostGreSQL):

SELECT * FROM "user";
-- or
SELECT * FROM public.user;

• Use ImprovedNamingStrategy: field and class names like “aPerfectAddress” will be transformed to “a_perfect_adress” when performing SQL queries. When creating the Hibernate's configuration (usually in HibernateUtil.java):

      Configuration cfg = new Configuration();
      cfg.setNamingStrategy(ImprovedNamingStrategy.INSTANCE);
      cfg.configure();

To generate the SQL schema accordingly with ant:

  <target name="schemaexport">
    <hibernatetool destdir="./">
     <configuration namingstrategy="org.hibernate.cfg.ImprovedNamingStrategy" configurationfile="${build.dir}/hibernate.cfg.xml"/>
      <hbm2ddl
          export="false"
          create="true"
          drop="false"
          delimiter=";"
          outputfilename="schema-export.sql"/>
    </hibernatetool>
  </target>

• for String fields, specify type=“text” (to avoid SQL varchar issues)

Example:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 
<hibernate-mapping package="ca.sfm.entity.characters">
 
  <class name="Toto">
    <id name="id">
      <generator class="native"/>
    </id>
    <version name="version"/>
    <property name="aPerfectAddress" type="text"/>
    <property name="mySecretAge" />
  </class>
 
</hibernate-mapping>

Notion of automatic dirty checking. Flushing is the process of synchronizing the memory state with the database. Updating makes a detached object persistent again (binds it to a new unit of work): so the actual database data will be updated.

Bi-directional links: it's important to set the link on both sides. All bi-directional associations need one side as inverse.

Sets: a defensive programming method is to set the getter/setter as protected, and add addToAnimals and removeFromAnimals methods.

Use one Hibernate session per request.

setFlushMode(FlushMode.MANUAL) is for read-only transactions. Test if it actually speeds things up.Ref

crit.createAlias(“parent”, “parent”, CriteriaSpecification.LEFT_JOIN); Create an alias without excluding those with parent==null