This is the GSP code generated by Grails for the view of the edit action for a Person domain object which is part of my model, and also happens to be the primary class for authentication by the ACEGI security plug-in. I have snipped out a bunch of properties to keep it short. The file resides in the standard location, grails-app/views/person/edit.gsp
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<meta name="layout" content="main" />
<g:set var="entityName" value="${message(code: 'person.label', default: 'Person')}" />
<title><g:message code="default.edit.label" args="[entityName]" /></title>
</head>
<body>
<div class="nav">
<span class="menuButton"><a class="home" href="${createLink(uri: '/')}">Home</a></span>
<span class="menuButton"><g:link class="list" action="list"><g:message code="default.list.label" args="[entityName]" /></g:link></span>
<span class="menuButton"><g:link class="create" action="create"><g:message code="default.new.label" args="[entityName]" /></g:link></span>
</div>
<div class="body">
<h1><g:message code="default.edit.label" args="[entityName]" /></h1>
<g:if test="${flash.message}">
<div class="message">${flash.message}</div>
</g:if>
<g:hasErrors bean="${personInstance}">
<div class="errors">
<g:renderErrors bean="${personInstance}" as="list" />
</div>
</g:hasErrors>
<g:form method="post" >
<g:hiddenField name="id" value="${personInstance?.id}" />
<g:hiddenField name="version" value="${personInstance?.version}" />
<div class="dialog">
<table>
<tbody>
<tr class="prop">
<td valign="top" class="name">
<label for="username"><g:message code="person.username.label" default="Username" /></label>
</td>
<td valign="top" class="value ${hasErrors(bean: personInstance, field: 'username', 'errors')}">
<g:textField name="username" value="${personInstance?.username}" />
</td>
</tr>
...SNIP...
a bunch of props
</tbody>
</table>
</div>
<div class="buttons">
<span class="button"><g:actionSubmit class="save" action="update" value="${message(code: 'default.button.update.label', default: 'Update')}" /></span>
<span class="button"><g:actionSubmit class="delete" action="delete" value="${message(code: 'default.button.delete.label', default: 'Delete')}" onclick="return confirm('${message(code: 'default.button.delete.confirm.message', default: 'Are you sure?')}');" /></span>
</div>
</g:form>
</div>
</body>
</html>
My question is, how does the field personInstance get set up and populated?
I suspect this is a basic question which belies a fundamental lack of understanding on my part about how Grails works, but I need to know nonetheless.
This stems from the desire to create my own composite pages which access a Person object and its associated data, which is the heart of my app. I was expecting to be able to create a new page alongside this one, let's call it map.gsp, and get at the personInstance in some magic way. I can't figure out how to do that in spite of trying the obvious, and I think I have a gap right at the centre of my understanding.