Why Grails Is Good

Obviously I can't say that Grails is the best thing since sliced bread and then not present some evidence to support my claim, so here's a specific example.

In my application I have a Network domain class and some other domain classes that extend it - TwitterNetwork, FacebookNetwork, etc. I wanted to handle the CRUD functionality for these classes in a single controller, but keep the forms separate. Having auto-generated the controller + views and then deleted the stuff I didn't want, here's the structure I ended up with:

- grails-app
  - domain
    - Network.groovy
    - FacebookNetwork.groovy
    - TwitterNetwork.groovy
  - controllers
    - NetworkController.groovy
  - views
    - network
      - list.gsp
    - facebookNetwork
      - create.gsp
      - edit.gsp
    - twitterNetwork
      - create.gsp
      - edit.gsp

Out of the box, the default list action just works:

def list = {
  if (!params.max) params.max = 10
  [ networkInstanceList: Network.list(params) ]
}

As do the delete, save and update actions.

All I have to do now is get the edit and create actions to use the correct view, depending on the network type. To do this I use the class name to determine which view to use. For example, here's my edit action:

def edit = {
  def networkInstance = Network.get(params.id)
  renderEditForm(networkInstance)
}

def renderEditForm(network) {
  def map = [ networkInstance : network ]
  def viewPath = getViewPath(network)
  render(view:"/${viewPath}/edit", model:map) 
}

// derive the view path from the given network instance
def getViewPath(network) {
  def networkName = getName(network)
  networkName[0].toLowerCase() + networkName[1..-1]
}

The great thing is, I know that will work because by convention Grails will put the views for TwitterNetwork in the twitterNetwork folder and the views for FacebookNetwork in the facebookNetwork folder. It then becomes a simple case of taking the class name and making the first character lower case.

I use the same principle for my create action:

static networks = [ "twitter" : TwitterNetwork,
                    "facebook" : FacebookNetwork ]
    
def create = {
  def networkInstance = createNetwork(params.type)
  networkInstance.properties = params
  renderCreateForm(networkInstance, params.type)
}

// create a new network instance of the given type
def createNetwork(networkType) {
  if (networkType in networks.keySet()) {
    def clazz = networks[networkType]
    return clazz.newInstance()
  }
}

... etc

And that's it! Full CRUD functionality for a set of polymorphic domain classes in a few lines of code - most of which were auto-generated by the framework. :-)