Populations of abstract classes are not listed in index

[amador-duran-toro]

In Grails 4.0.3 and Grails 3.3.11, if you have an inheritance hierarchy with an abstract superclass, e.g.

package mypackage

abstract class A {
  String name
  // ...
  // properties
  // ...
}

package mypackage

class B extends A {
  String b
  // ...
  // properties
  // ...
}

package mypackage

class C extends A {
  String c
  // ...
  // properties
  // ...
}

And you populate the concrete classes in Bootstrap.groovy, e.g.

package mypackage

class BootStrap {

    def init = { servletContext ->
        A.withTransaction { status ->
            def listOfB = []
            (1..25).each { i ->
                listOfB << new B(name:"b${i}",b:"${i}st")
            }

            B.saveAll( listOfB )

            def listOfC = []
            (1..25).each { i ->
                listOfC << new C(name:"c${i}",c:"${i}nd")
            }

            C.saveAll( listOfC )
        }
    }
    def destroy = {
    }
}

If you use scaffolding, the index page for A shows an empty list instead of a paginated list of 50 objects (25 B objects and other 25 C objects).

Apart from that, it shows a new button that generates a java.lang.InstantiationException when clicked because it tries to instantiate an abstract class.

A quick and dirty workaround for this problem is the following:

1. Generate views for the abstract class (only index.gsp is relevant)
2. Edit the generated index.gsp in the following way:

• Comment the new button code

<!-- no create button -->
<!--
<li><g:link class="create" action="create"><g:message code="default.new.label" args="[entityName]" /></g:link></li>
-->

• Comment the <f:table> element and add the following code

<!-- new arguments for f:table -->
<g:set var="collection" value="${mypackage.A.list(params)}" />
<g:set var="domainClass" value="${grailsApplication.getDomainClass('mypackage.A')}" />
<g:set var="domainProperties" value="${domainClass.getConstrainedProperties().keySet()}" />
<!-- old f:table -->
<!-- <f:table collection="${aList}" /> -->
<!-- new f:table -->
<f:table collection="${collection}" properties="${domainProperties}" />            

With respect to <f:table> attributes:

• The aList variable originally passed to <f:table> is null.
• Do not include domainClass="mypackage.A", it generates a java.lang.InstantiationException.
• The properties attribute must be present and contain the list of properties of the abstract class only. If it is not present, and objects of classes A and B appear in the same pagination, a org.springframework.beans.NotReadablePropertyException is thrown because <f:table> tries to read properties of class B on objects of class C and viceversa.

Apart from that, the create and edit pages are still available for A. I have generated-all for A and tried to delete those methods from the generated controller, but my knowledge of Grails is limited and I am having lots of errors with that, so I went back to scaffolding (which is my main reason for using Grails).

I think that Grails should not show empty lists for abstract classes in scaffolding, but I do not know if that behaviour is inside the scaffolding controller, the <f:table> tag, or harcoded in _table.gsp.

I also think that Grails should not generate create and update methods in the scaffolding controllers for abstract classes.