Dynamic mapping with hibernate

In this post I will share my experience in implementing dynamic mapping with hibernate. The idea is to write generic code that can be made to query data from any table with any no.of columns, ofcourse the actual table & column information is provided as a configuration.

1. Use dynamic map entity mode
This can be done by adding the following in your hibernate.cfg.xml:

<property name="default_entity_mode">dynamic-map</property>

2. Now provide the mapping, this is the only part where you provide the actual table & column details, just changing this will suffice if new columns are added or if you intend to reuse this code to query some other table.

Following is an example:

<class entity-name="TestEntity" table="ENTITY">
    <id name="id"  type="long" column="ID">
          <generator class="sequence"/>
    </id>

    <property name="title" column="TITLE" type="string"/>
    <property name="text" column="TEXT" type="string"/>
</class>

3. Code to query the table:

  SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();

  Session s = sessionFactory.openSession();

   // Retrieve the data.
    String QUERY ="from TestEntity"; // Should use the entity name as defined in the hibernate mapping.
     Query query = s.createQuery(QUERY);
     HashMap<String, Object> temap = null;
     for(Iterator it=query.iterate();it.hasNext();){
       temap =(HashMap<String, Object>)it.next();  // for each row you get a map.
       // copy the map contents to your object or add to some list as needed.

     }


4. Similarly inserting can be done by creating a map with all the column/value pairs and then

Map teMap = new HashMap<String,Object>();

// fill the map with the column names & values.

s.save("TestEntity", teMap);


This can also be extended to generate the web client code based on the configuration, for example if you use extjs as the javascript framework to build the web ui, then the above can be exposed as restful service and then the table can be dynamically created based on the columns in the DB table.  I will explore that in my next post.