4 Flow Execution Events - Reference Documentation
Authors: Graeme Rocher
Version: 2.1.0
4 Flow Execution Events
In order to transition execution of a flow from one state to the next you need some way of trigger an event that indicates what the flow should do next. Events can be triggered from either view states or action states.Triggering Events from a View State
As discussed previously the start state of the flow in a previous code listing deals with two possible events. Acheckout
event and a continueShopping
event:def shoppingCartFlow = { showCart { on("checkout").to "enterPersonalDetails" on("continueShopping").to "displayCatalogue" } … }
showCart
event is a view state it will render the view grails-app/book/shoppingCart/showCart.gsp
. Within this view you need to have components that trigger flow execution. On a form this can be done use the tags tag:<g:form> <g:submitButton name="continueShopping" value="Continue Shopping" /> <g:submitButton name="checkout" value="Checkout" /> </g:form>
shoppingCart
flow. The name attribute of each tags tag signals which event will be triggered. If you don't have a form you can also trigger an event with the tags tag as follows:<g:link event="checkout" />
Prior to 2.0.0, it was required to specify the controller and/or action in forms and links, which caused the url to change when entering a subflow state. When the controller and action are not specified, all url's are relative to the main flow execution url, which makes your flows reusable as subflows and prevents issues with the browser's back button.
Triggering Events from an Action
To trigger an event from anaction
you invoke a method. For example there is the built in error()
and success()
methods. The example below triggers the error()
event on validation failure in a transition action:enterPersonalDetails { on("submit") { def p = new Person(params) flow.person = p if (!p.validate()) return error() }.to "enterShipping" on("return").to "showCart" }
enterPersonalDetails
state.With an action state you can also trigger events to redirect flow:shippingNeeded { action { if (params.shippingRequired) yes() else no() } on("yes").to "enterShipping" on("no").to "enterPayment" }