Hibernate Aggregate Functions(Associations and Joins)
This example tries to make understand about the aggregate function of
Hibernate with the help of example.
In Hibernate HQL queries are capable of returning the
results of the aggregate functions on properties. Collections can also be
used with the aggregate functions with the select clause. Aggregate functions
supports the following functions:
- min(...), max(...), sum(...), avg(...).
- count(*)
- count(distinct...), count(all..), count(...)
The distinct and all keywords used above are identical
as in SQL.
A unidirectional one-to-many association on a
foreign key is rarely required.
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping
PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN"
"http://hibernate.sourceforge.net
/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="net.roseindia.Dealer">
<id name="id" type="int">
<generator class="increment"/>
</id>
<property name="name" type="string"/>
<bag name="product" inverse="true"
cascade="all,delete-orphan">
<key column="did"/>
<one-to-many class="net.roseindia.Product"/>
</bag>
</class>
</hibernate-mapping>
|
A unidirectional one-to-many association on a
foreign key is rarely required.
<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-mapping
PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN"
"http://hibernate.sourceforge.net/
hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="net.roseindia.Product">
<id name="id" type="int">
<generator class="increment"/>
</id>
<property name="name" type="string"/>
<property name="did" type="int"/>
<property name="price" type="double"/>
<many-to-one name="dealer" class="
net.roseindia.Dealer" column="did"
insert="false" update="false"/>
</class>
</hibernate-mapping>
|
In this example first we create the session object with
the help of the SessionFactory interface. Then we use the createQuery() method
of the Session object which returns a Query object. Now we use the openSession()
method of the SessionFactory interface simply to instantiate the Session object.
And the we retrieve the data from the database store it in that Query object and
iterate this object with the help of Iterator and finally displays the requested
data on the console.
Here is the hibernate code:
package net.roseindia;
import java.util.Iterator;
import java.util.List;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class AggregateFunctionExample {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Session sess = null;
try{
SessionFactory fact = new
Configuration().configure().buildSessionFactory();
sess = fact.openSession();
String sql_query = "select
d.name,p.name,sum(p.price) as
totalprice from Product
p join p.dealer d group by p.name";
Query query = sess.createQuery(sql_query);
System.out.println("Dealer
Name\t"+"Product Name\t"+"Price");
for(Iterator it=
query.iterate();it.hasNext();){
Object[] row = (Object[]) it.next();
System.out.print(row[0]);
System.out.print("\t\t"+row[1]);
System.out.print("\t"+row[2]);
System.out.println();
}
sess.close();
}
catch(Exception e ){
System.out.println(e.getMessage());
}
}
}
|
Output:
| log4j:WARN No
appenders could be found for logger (org.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
Hibernate: select dealer1_.name as col_0_0_, product0_.name as
col_1_0_, sum(product0_.price) as col_2_0_ from Product product0_ inner
join Dealer dealer1_ on product0_.did=dealer1_.id group by product0_.name
Dealer Name Product
Name Price
Agrawal
Computer
23100.0
Ritu
HardDisk
2500.0
Agrawal
Keyboard
1500.0
Ritu
Laptop
200.0
Mohan
Mobile
15000.0
Mohan
PenDrive
200.0
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