I won't give you a full answer, as it is too long to explain.
Basically, after ejbCreate has been called, the entity exists and has a primary key.
What you can do in doPostCreate is setting the CMR fields for example.
You can get the primary key by calling getPrimaryKey(). You can pass a reference to the component interface of the bean to another bean.
if there is no create method , then how entity will be created ,is it created by finder method ?
You're misunderstanding the concept of ejbCreate. ejbCreate will insert some data in a persistent store.
Finder methods only looks for data, and the retrieved data is set into a bean by the container.
Create methods are not called here.