Grails - check if item has parent - grails

Question

I'm new to Grails, Groovy and GSP.
I have a domain class "ProductCategory".
class ProductCategory {
static constraints = {
}
static mapping = {
table 'product_category';
version false;
cache usage: 'read-only';
columns {
parent column: 'parentid';
procedure column: 'procid';
}
}
static hasMany = [children:ProductCategory];
ProductProcedure procedure;
Integer lineorder;
String name;
ProductCategory parent;
String templatelink;
char offline;
String toString() {
return id + " (" + name + ")";
}
}
Each category CAN have a parent. I am using an existing database, and the table has a column 'parentid' to do that. When a category has no parent (root level), its parentid is 0.
I have a GSP trying to show data about the parent if any.
<g:if test="${category.parent}">
hello
</g:if>
I was under the impression that this would test for existence.
It works fine if the category DOES have a parent, but as soon as parentid=0, it blows up.
No row with the given identifier exists: [ProductCategory#0]
I tried to check for ==0, but it didn't work, I assume because 'parent' is supposed to be an object.
So how can I make it so that it assumes that parentid=0 is the same as parent=null, or NO parent?
Thanks

Answer 1

I think I may have found the answer:
parent column: 'parentid', ignoreNotFound: true;
ignoreNotFound is nowhere on the documentation, but it seems to work!

Answer 2

parentid should not be equal to 0. It should be null.
What I don't understand in your question, is how can you have parentid == 0 ?

Answer 3

You don't need to handle the parentid manually. As soon as you define a domain class like this:
Class Foo {
Bar bar
}
Gorm/Grails will automatically create a foreign key column for you. And if you define the property nullable:
Class Foo {
Bar bar
static constraints = {
bar(nullable:true)
}
}
...you can just set it to null and test for null:
def f = new Foo(bar:null)
if (f.bar == null) { ... }