The JPA Architecture

Today, in this final post of the semester for CS-343 I will be examining the JPA architecture. This is something I have been curious about after browsing articles on DZone for the past couple of weeks and seeing this topic pop up a lot, luckily they made a good introduction post this week. From the article: “The Java Persistence API is the Java standard for mapping Java objects to a relational database”, this is something that I have been wondering how to do since we started working with the REST APIs and our projects that have been using Java HashMaps for makeshift databases instead of something more permanent like SQL. This article briefly introduces and explains the functionality of the six key parts of the architecture for JPA. The article gives a diagram for these six units and the multiplicity of their relationships. The article then gives a simple example of mapping a simple Java POJO Student class into data for a database, using the student ID as the primary key. I was surprised at how easy this translation was, all it includes is a couple of tags for columns above the instance variables that designate the database column, and which one is the primary key to generate in the database. The article then creates an application class that uses the various entity classes to store a newly created student into a database. I liked the simplicity of the article as most introductory articles are on this website for what are advanced programming topics, but my biggest criticism is that this article has brief definitions for many of the elements of JPA and then links to an external site that further elaborates on them. I wished that the author put a bit more time and consolidated all of this information into one article for this site, instead of having a bunch of separate webpages on his own website. I also wish he showed in this post getting data from the database and translating it back into Java and performing manipulations on this data with methods. Overall it was a good introduction to a very useful topic and one that I would like to further look at. Going forward, I am much in favor of using this way of storing data as opposed to simple Java in-memory databases for entire applications like we did in our projects.



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