Mapping Composite Keys in Hibernate

In Real world applications it is natural to have tables with composite keys. The row will be identified with combination of key  column values of a row.

Consider Following scenario:

A test selling website defines tests and customers.

   create table test(
   test_id int(11) not null auto_increment,
   test_name varchar(100),
   test_desc varchar(150),
   test_questions varchar(5),
   primary key(test_id));

   create table customer(
       customer_id int(11) not null auto_increment,
       name varchar(50) not null,
       email_id varchar(100),
       contact_no varchar(20),
       primary key(customer_id));

To keep track of tests purchased by customers it maintains following table:

   create table tests_purchased(
   customer_id int(11) not null,
   test_id int(11) not null,
   created_date datetime not null,
   primary key(customer_id, test_id));

Primary key of this table is combination of customer and test id.
To map such classes we have to use <composite-key> tag.  Both the test_id and customer_id acts as identifier to the tests_purchased table.

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