JDK 7 UPDATE 80 AND NETBEANS IDE 8.0.2 DOWNLOAD FOR WINDOWS UPDATEIn JPA I need to remind myself that each time I have a one-to-many relationship I need to manually link them together or it doesn’t update automatically/only updates after application is restarted. In Rails this sort of things is done automatically, and it should be. I’m going to be a bit honest here: this is kinda inconvenient, and retarded. PostId.getCommentCollection().add(this) // programmer needs to add this himself JDK 7 UPDATE 80 AND NETBEANS IDE 8.0.2 DOWNLOAD FOR WINDOWS CODEBy that it meant that it is the responsibility of the programmer to manually code in the links when a setter is called: This is because (as aggravating as it sounds) in JPA, it is the responsibility of the application, or the object model to maintain relationships. Here’s how my setPostId function in my Comment entity looks like: I would have thought that JPA would update the Comments collection inside the Post, but it didn’t. I don’t see the changes immediately though had to restart the application to see the new Comments. I had this issue that when I add a one to many relationship: Post has many Comments, now I add a Comment to a Post. You Need to Manually Manage One To Many Relationships If (im().isEmpty()) return // empty strings begone!Īs you can imagine, I have to do this for every attribute in every entity that doesn’t accept empty strings. There are workarounds for this online: one of them was using the annotations or Unfortunately I’m using Java SE 8 is currently supported up to Java EE 7 as of this writing) and I’m not using Spring (for what I ended up doing was place the validation in the setter method: This kind of shit doesn’t happen when simply working with raw SQL strings. It is actually stored in the database as “”. Yet for some reason a string “” is not a null value in JPA. In my DDL, I have a rule that Post cannot have null value for Name attribute. There’s still one more issue that I’ll get to next: Empty Strings are not Null Well, this output doesn’t just happen automatically. The following dialog should pop up when the Author field is empty: or some shit like that", JOptionPane.ERROR_MESSAGE) JOptionPane.showMessageDialog(this, ex.toString(), "Invalid content. JOptionPane.showMessageDialog(this, "Post has successfully been added.", "Successfully added post!", JOptionPane.INFORMATION_MESSAGE) ĭispatchEvent(new WindowEvent(this, WindowEvent.WINDOW_CLOSING)) PreparedStatement ps = core.DB.getInstance().getPreparedStatement(sql) String sql = "INSERT INTO post (name, title, content) VALUES (?, ?, ?)" I don’t exactly know what was the reason the exception was happening in runtime, but without the try-catch block, the procedure is going to fail (Here the Post entity cannot have null value for Name attribute) silently. The problem? It’s a subclass of RuntimeException. Aren’t there exceptions? Well, turns out there’s PersistenceException. But what’s weird was that it offered to remove the try-catch block as a solution! Wow wow wow, stop. So when converting the code, I realized that in the places where SQLException would appear, Netbeans puts up an error saying that SQLException doesn’t happen here: Here is the dateCreated attribute inside = Date dateCreated = new Date() // new Date() returns the current timestamp The workaround is to code the default values into the attribute field of the entity classes. So all the SQL code where I have DEFAULT is basically replaced with null when I use JPA. So each time I create a Post, I’m expecting the date_created attribute to show the current date, but it doesn’t. Id INT PRIMARY KEY GENERATED ALWAYS AS IDENTITY(START WITH 1, INCREMENT BY 1),ĭate_created TIMESTAMP DEFAULT CURRENT_TIMESTAMP I noticed something strange when adding a Post entity: the created_date attribute shows up as a null when I convert to use JPA. My DDL (Database Definition Language) looks like this (Derby DB SQL): List rs = db.createQuery("SELECT p FROM Post p ORDER BY p.dateCreated DESC").getResultList() ResultSet rs = db.executeQuery("SELECT * FROM post ORDER BY date_created DESC") This isn’t much an issue really in the long run it does you a favour since it is database vendor independent. SQL needs to be rewritten to Java Persistence Query Language Netbeans makes the initial setup very simple by generating persistence.xml (you find the persistence unit name here) for you, as well as the the entities for you from your database. You can view all the changes to convert to JPA in this Github diff. JDK 7 UPDATE 80 AND NETBEANS IDE 8.0.2 DOWNLOAD FOR WINDOWS ZIPIf you don’t use git you can download this sample project as a zip from MediaFire. The finished product is in a git branch called JPA. I will be converting a simple application from “ Generic Java GUI Netbeans Project with Embedded Database” that only has 2 entities: Post and Comment. In this post I walk through some of the gotchas when converting a java application that works with raw SQL strings to one using ORM (Object Relational Mapping) via JPA (Java Persistence API).
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