Creating a primary key and composite primary key column – @Id and @IdClass

It's necessary to declare an Identity column in each class while developing with hibernate. Sometimes, when we need to declare a primary key as a combination of multiple columns, we call this the composite primary key, as the primary key is composed of multiple columns. We can declare a column with the primary key constraint and also generate a composite primary key using hibernate.

How to do it…

Let's start with a primary key declaration:

1. To declare a column as a primary key column, we use the @Id annotation, as follows:

   @Id
   private long id;

   When the preceding code is executed, hibernate creates a column with the name id and also adds the primary key index to it. In this case, @Column is not required unless you want a custom column name.

2. To declare it as a composite primary key, we will consider creating a composite primary key using the employee's first name and phone. Therefore, the firstName column will be duplicated...