I am not even sure if this is possible, my use case is as described.

I have a table, say Book, and it has a primary key say book_id which is of varchar2 type. The values for this column are of the format [F|N][0-9]*[DDMMYYYYHHMISS] format. ie. say example, F4358622032011123423 or N5358622032011123423, etc. where the first part is provided by the application (F stands for fiction, N stands for non-fiction) , middle numeric part is actually database sequence generated number and the third part is system timestamp.

I can map the middle part using the following mapping:

<class name="Book" table="book">
<id name="bookId" type="long" colum="book_id">
<generator class="sequence">
<param name="sequence">seq_book</param>
</generator>
</id>
.....
.....
.....
</class>

however, is there any possible way for me to delegate the creation of the entire expression(as described above) to hibernate itself. Is there a way for hibernate to evaluate an expression and add as a sequence ( for ex: say just the sequence generated number+ date timestamp)

Currently i use an utility class to generate the expression and set the returned string value to the field bookId of the Book entity. And my current mapping is as below:

<class name="Book" table="book">
<id name="bookId" type="string" colum="book_id" />
.....
.....
.....
</class>

I would appreciate any help regarding this.