The majority of complex programs use persistent data: GUI applications need to store user preferences across program invocations, web applications track user movements and orders over long periods of time, etc.

xml error validating datastore indexes xml against datastore indexes xsd-58

There are no special parent classes to extend from, field types to use, or methods to write.

This is one important way in which JPA makes persistence transparent to you, the developer.

It also assumes some experience with relational databases and the Structured Query Language (SQL).

is information that can outlive the program that creates it.

A version field is not required, but without one concurrent threads or processes might succeed in making conflicting changes to the same record at the same time. Section 2.5, “ Version ” shows you how to designate a version field in JPA metadata.

The version field must be an integral type ( Open JPA fully supports version fields, but does not require them for concurrency detection.

When the JPA runtime detects an attempt to concurrently modify the same record, it throws an exception to the transaction attempting to commit last.

This prevents overwriting the previous commit with stale data.

For example, Java serialization is a form of lightweight persistence because it can be used to persist Java objects directly to a file with very little effort.