CascadeType Explained

PERSIST

maps to EnityManager.persist(). Make an instance managed and persistent.

MERGE

maps to EnityManager.merge(). Merge the state of the given entity into the current persistence context.

REMOVE

maps to EnityManager.remove(). Remove the entity instance.

REFRESH

maps to EnityManager.refresh(). Refresh the state of the instance from the database, overwriting changes made to the entity, if any.

ALL

all of the above

References

Java Persistence with Hibernate

Christian Bauer, Gavin King

What is the biggest source of bugs in Software?

Riddle:What is the biggest source of bugs in Software?

Solution: Software Designers

Composite Primary Keys

Besides Java, I do have a lot to do, as do we all, I presume, with Database and Database Administration and Database Design.

In my current job, I see a lot of code where a join table has a single column, an autogenerated id, for a Primary Key. And it's really annoying.

Due to lack of proper unique indexes, there are a lot of duplicate records in the table, only they're not duplicate because they have a unique Primary Key (an autogenerated id).

If the table is a perfect example of a way of joining two tables together, there is no reason not to have a combined Primary Key consisting of the two foreign keys used to join the other two tables together.

Example:

Table:

User

id

Table:

Widget

id

Bad Example:

Join Table:

User_Widget

id

user_id

widget_id

Good Example:

Join Table:

User_Widget

user_id

widget_id

In the good example, the constraints of the Primary Key take care of everything, it's quicker, it's more efficient, and it's always correct.

Yahoo Web Best Practices

One of the most enlightening articles I've read in a long time, regarding the responsiveness (and the way to increase it) of websites. http://developer.yahoo.com/performance/rules.html#page-nav