Hi all,
Is it necessary to have id column in every table having generator class
as" increment","uuid.hex" etc.Doing in this way we are adding an extra column in the table.

But if we use generator class as "assigned" then we can make a column of the table as primary key.So in this case there is no extra column is getting added.

I want to know wheather second approach is correct or not?Does it have any
limitation?

with regards,
ajse

The second style you mention, is basically using a business key as the id, correct?

This is discouraged because at design time, although you may believe a key to be both unique and unchangeable, business requirements change. For example, a naive implementation might use a company's name as the id for a company. If that company merges with another, the id becomes invalid, and the system's integrity is compromised.

Using an internal id will not take up that much space, esp. if you use a generator like the 'native' generator that uses numbers instead of strings. It means that your business entities can change as required to match the evolving design.

I believe that there are a number of other posts asking this question, more information is available with a little searching.