fix for GRAILS-3273 "Many-To-Many Mapping with Subclasses does not work"

Author: graemerocher

src/java/org/codehaus/groovy/grails/commons/DefaultGrailsDomainClass.java

@@ -52,7 +52,7 @@ public class DefaultGrailsDomainClass extends AbstractGrailsClass  implements Gr
     private Map mappedBy;
     private Validator validator;
     private String mappingStrategy = GrailsDomainClass.GORM;
-    private List owners = new ArrayList();
+    private List<Class> owners = new ArrayList<Class>();
     private boolean root = true;
     private Set subClasses = new HashSet();
     private Collection embedded;
@@ -406,13 +406,16 @@ private void establishOwnerOfManyToMany(DefaultGrailsDomainClassProperty propert
     	Object related = BeanUtils.instantiateClass(relatedClassType);
     	Object relatedBelongsTo = GrailsClassUtils.getPropertyOrStaticPropertyOrFieldValue(related, GrailsDomainClassProperty.BELONGS_TO);
     	boolean owningSide = false;
-    	boolean relatedOwner = this.owners.contains(relatedClassType);
+    	boolean relatedOwner = isOwningSide(relatedClassType, this.owners);
     	final Class propertyClass = property.getDomainClass().getClazz();
     	if(relatedBelongsTo instanceof Collection) {
-			owningSide = ((Collection)relatedBelongsTo).contains(propertyClass);
+			final Collection associatedOwners = (Collection)relatedBelongsTo;
+			owningSide = isOwningSide(propertyClass, associatedOwners);
     	}
-    	else if (relatedBelongsTo != null) {
-    		owningSide = relatedBelongsTo.equals(propertyClass);
+    	else if (relatedBelongsTo instanceof Class) {
+    		final Collection associatedOwners = new ArrayList();
+    		associatedOwners.add(relatedBelongsTo);
+    		owningSide = isOwningSide(propertyClass, associatedOwners);
     	}
     	property.setOwningSide(owningSide);
     	if(relatedOwner && property.isOwningSide()) {
@@ -422,6 +425,15 @@ else if(!relatedOwner && !property.isOwningSide() && !(property.isCircular() &&
     		throw new GrailsDomainException("No owner defined between domain classes ["+propertyClass+"] and ["+relatedClassType+"] in a many-to-many relationship. Example: def belongsTo = "+relatedClassType.getName());
     	}
 	}
+	private boolean isOwningSide(Class relatedClassType, Collection<Class> owners) {
+		boolean relatedOwner = false;
+    	for (Class relatedClass : owners) {
+			if(relatedClass.isAssignableFrom(relatedClassType)) {
+				relatedOwner = true; break;
+			}
+		}
+		return relatedOwner;
+	}
 
 	/**
      * Establishes whether the relationship is a bi-directional or uni-directional one-to-many

src/java/org/codehaus/groovy/grails/orm/hibernate/ManyToManyWithInheritanceTests.groovy

@@ -0,0 +1,46 @@
+package org.codehaus.groovy.grails.orm.hibernate;
+
+class ManyToManyWithInheritanceTests extends AbstractGrailsHibernateTests {
+
+	@Override
+	protected void onSetUp() {
+		gcl.parseClass '''
+import grails.persistence.*
+
+@Entity
+class Pentagon extends Shape{
+
+}
+@Entity
+class Shape {       
+	static hasMany = [attributes:ShapeAttribute]
+}
+@Entity
+class ShapeAttribute{
+
+	String name
+	String value
+	
+	static hasMany = [shapes: Shape]
+	static belongsTo = Shape
+
+}
+'''
+	}
+	
+	void testManyToManyMappingWithInheritance() {
+		def Pentagon = ga.getDomainClass("Pentagon").clazz
+		def ShapeAttribute = ga.getDomainClass("ShapeAttribute").clazz
+		
+		def p = Pentagon.newInstance()
+		p.addToAttributes(name:"sides", value:"5")
+		
+		assert p.save(flush:true) : "should have saved instance"
+			
+		session.clear()
+		
+		p = Pentagon.get(1)
+		
+		assert 1 == p.attributes.size() : "should have one attribute"
+	}
+}