GORM Inheritance & Relationships

Trying out GRAILS today, I came across an odd bug – or is it a feature? Before I get into details a class diagram of the problem at hand

I have the super class Shape, which should reference a list of ShapeAttributes. I therefore expect all sub classes  of Shape (i.e. Square and Triangle) to also have a reference to a list of ShapeAttributes. On top of that I also want to have a bi-directional relationship, so I can list all shapes (regardless of concrete implementation) from a single ShapeAttribute instance.

Here are my domain classes:

class Shape {       

static hasMany = [attributes:ShapeAttribute]

}

class Square extends Shape {

}

class Triangle extends Shape{

}

class ShapeAttribute{

String name

String value

static hasMany = [shapes: Shape]

static belongsTo = Shape

}

To test all of this I wrote the following integration test:

void testSimpleInheritance() {

def triangle = new Triangle()

def square = new Square()

def shape = new Shape()

def lengthAtt = new ShapeAttribute(name: "length", value: "value")

def shapeAtt = new ShapeAttribute(name: "type", value: "not specific")

def triangleAtt = new ShapeAttribute(name: "type", value: "triangle")

def squareAtt = new ShapeAttribute(name: "type", value: "square")

                                                                            

shape.addToAttributes shapeAtt

shapeAtt.addToShapes(shape)

triangle.addToAttributes lengthAtt

triangle.addToAttributes triangleAtt

square.addToAttributes lengthAtt

square.addToAttributes triangleAtt 

    

shape.save()

triangle.save()

square.save()          

           

assert shape.attributes.size() == 1

assert triangle.attributes.size() == 2

assert square.attributes.size() == 2

assert shapeAtt.shapes.size() == 1

assert lengthAtt.shapes.size() == 2

assert triangleAtt.shapes.size() == 1

assert squareAtt.shapes.size() == 1

}   

But the compilation of all this fails due to:

     [copy] Copying 1 file to /Users/stefansiprell/.grails/1.0.3/projects/scratchpad

org.codehaus.groovy.grails.exceptions.GrailsDomainException: No owner defined between domain classes [class Triangle] and [class ShapeAttribute] in a many-to-many relationship. Example: def belongsTo = ShapeAttribute

It seems to me, that GRAILS knows that Triangle should have a list of Attributes, but it does not know that Triangle should be the managing (i.e. belongsTo) part. What am I doing wrong? Or where is GRAILS failing?