Accessing databases in servicemix-drools

ServiceMix provides a Service Engine for Drools, the famous Rules Engine.

People often want to retrieve data from the rules and such data is usually stored in a database. Previously there was no easy way to configure a DataSource and inject it in the rules definitions. This is a small enhancement that I've just written and that will be included in next major release.

So let's say you write your database access code in a simple helper object:

import javax.sql.DataSource;
import org.springframework.jdbc.core.JdbcTemplate;

public class DbHelper {
    private DataSource dataSource;
    private JdbcTemplate jdbcTemplate;

    public void setDataSource(DataSource dataSource) {
      this.dataSource = dataSource;
      this.jdbcTemplate = new JdbcTemplate(dataSource);
      this.jdbcTemplate.afterPropertiesSet();
    }

    public String getSurname(String name) {
        String surname = (String) this.jdbcTemplate
          .queryForObject(
              "select surname from t_actor where name = ?", 
              new Object[]{name}, String.class);
    }
}

Now, let's use it in our rule definition:

import org.apache.servicemix.drools.model.Exchange;
global org.apache.servicemix.drools.model.JbiHelper jbi;
global DbHelper helper;

rule Init
    when
        $me : Exchange()
    then
        String t = $me.getIn().getContent().getTextContent();
        jbi.answer("<surname>"
            + helper.getSurname(t)
            + "</surname>");
end

And the xbean.xml would look like:

<drools:endpoint  service="test:service"
                  endpoint="endpoint"
                  ruleBaseResource="classpath:router.drl"
                  globals="#globals" />
<util:map id="globals">
  <entry key="helper" value-ref="helper" />
</util:map>
<bean id="helper" class="DbHelper">
  <property name="dataSource">
    <bean class="org.springframework.jndi.JndiObjectFactoryBean">
      <property name="jndiName" value="java:myDataBase" /> 
    </bean>
  </property>
</bean>

This will make available the helper bean to the rules while initializing it with a DataSource looked up from JNDI.

Happy hacking !