Sometimes, people may ask it to associated with a View in DB. Headaches are here...
Some people try to avoid mapp an Entitybean to a View in DB. They choose to desigb bigger tables.
One of my friends has ever designed a table with 16 column because his EntityBean has 16 attributes. I did not dispute with him because he is my friends. But I do think his design is problamatic. From my perspective, a Table iwth 16 columns is likely to be a poorly normalized one.
Many people are doing EJB projects but the performance is generally poor.
I don't think you need finsih the whole book.
EJB Specification is a reference, not a textbook. I think following some examples shipped with EJB container is more useful than going through the whole book.