It's a common story. You have an existing database and now you want to add a web application for it with the minimum of fuss. Is Grails up to the task? Of course it is! Even better, if you already have a domain model based on JPA or Hibernate configuration files, you can reuse it and still benefit from the great GORM features you're used to. The first step in reusing an existing domain model is to get the class files on the application's classpath. You can do this either by packaging them up in a JAR file and including it in the application (typically by dropping it in the 'lib' directory), or…

RabbitMQ is a lightweight, reliable, scalable and portable message broker based on the Advanced Message Queueing Protocol (AMQP). It's ideal for heterogeneous systems and cloud platforms, but it can be used for pretty much any messaging requirements, big or small. You don't (typically) access it via the JMS API, and in fact the JMS plugin won't help, but a new plugin is now available that's dedicated to making it easy to use RabbitMQ from Grails applications. The current version of the plugin (0.2) is relatively limited, but you can already send and receive messages. I encourage you to try it…

Spring Security is a powerful library for securing your applications that comes with a bewildering number of options. Based on Spring, it can be readily integrated into a Grails application. But why not save the hassle and use the new improved Grails plugin? The plugin has gone through several evolutionary stages that started with the Acegi plugin. Its most recent incarnation is a complete rewrite for Spring Security 3 and Spring 3. One of the results of this is that the plugin will only work with Grails 1.2.2 and above. Another significant change is that there is no longer just one Spring…

It's great to hear that people are finding these articles useful, so it's with great pleasure that I add another to the series. This time I'm going to talk about associations again, but with the focus on when they are loaded into memory. Update 2 Aug 2010 I have added more information on eager fetching with one-to-many relationships because there are some issues you need to be aware of. One of the first things people learn about GORM relationships is that they are loaded lazily by default. In other words, when you fetch a domain instance from the database, none of its relations will be loaded…

In part 1 of this series, I introduced you to some of the subtleties associated with persisting domain instances with GORM. This time, I'm going to tackle relationships with particular focus on hasMany and belongsTo. GORM provides only a few basic elements for defining relationships between domain classes, but they are sufficient to describe most needs. When I give training courses on Grails, it always surprises me how few slides cover relationships. As you can imagine, this apparent simplicity does hide some subtle behaviour that can trip up the unwary. Let's start with the most basic of…

Are you new to Grails? Or have you perhaps run into your first GORM "oddity"? If so, then you'll want to read this series on GORM gotchas. Not only will the articles highlight those little idiosyncrasies that often catch people out, but they will also explain why GORM behaves in these ways. Hopefully you will already know that GORM is the database access library that comes with Grails. It's based on probably the most popular Java ORM out there: Hibernate. As you can imagine, Hibernate is a powerful and flexible library and it brings big benefits to GORM. But there is a cost to using it: many…

In the SpringSource training course for Groovy & Grails, we highlight that Grails stands on the shoulders of giants. One of those giants is Spring. Without it, Grails simply wouldn't have been developed as quickly as it was. It probably wouldn't have the flexibility to integrate easily with enterprise Java systems either. Just look at the number of plugins available: many are based on Java libraries with Spring support. In this post, I want to start by looking at how Grails uses Spring and then cover the various ways in which you can access that raw power and flexibility. Here are some…

Grails is a fantastic framework for developing web applications quickly and easily. You also have access to a plethora of plugins that provide features or make integration with other systems nice and easy. That's all good, but in this article I want to talk about what happens when your application grows and you start drowning in a sea of controllers, domain classes, and other files. The real beauty of this pattern is that you can aggregate these units into coarser-grained concerns, so you end up using the pattern at multiple levels. For example, say that the web service mentioned above…

Last week, I described how Grails now treats plugins like normal dependencies that can be pulled from Maven-compatible repositories. Although this was the big new feature for 1.3, it wasn't the only one. In this post, I'll look at some of the others, starting with a feature that I only recently found out about. Develop a non-trivial Grails application and you will soon realise that you often use the same queries again and again. What should you do? The copy-and-paste technique is simple but leaves you with major maintenance issues. You could write service methods for each of your common…