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Hibernate Mapping using xml

A mapping file in Hibernate is used to map the fields of a java class with the fields of the table in a relational database.

Let's follow the below steps.

CREATE A JAVA CLASS

Let us create a class named 'Employee' in java :

class Employee{
int empId;
String name;
---Getters & Setters---
}

CREATE A TABLE IN THE DATABASE

Similarly in the database let us create a table named EMPLOYEE :

CREATE TABLE EMPLOYEE (EMP_ID INTEGER, NAME VARCHAR, PRIMARY KEY (ID));

CREATE THE MAPPING FILE

Now, the mapping file would look like:

Employee.hbm.xml

<?xml version = "1.0" encoding = "utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
<class name = "Employee" table = "EMPLOYEE">

<id name = "empId" type = "int">
<column name = "EMP_ID">
</id>
<property name = "name" type = "string">
<column name = "NAME">
</property>

</class>
</hibernate-mapping>

The above mapping file says, to which table the java class will map to.

In the above case the Employee class is getting mapped to EMPLOYEE table.

The <id> tag specifies the primary key, where we have linked the class attribute (i.e. empId) with the column name (i.e. EMP_ID) of the EMPLOYEE table.

Finally, we have the <property> tag where we have linked the class attribute (i.e. name) with the column name (i.e. NAME).

Mapping can also be achieved using Annotations, which we will be looking later.

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