feat(validator): Add validation rule for associations to validator

src/index.js

@@ -1,8 +1,11 @@
 import {EntityManager} from './entity-manager';
+import {ValidationGroup} from 'aurelia-validation';
+import {HasAssociationValidationRule} from './validator/has-association';
 
 export {DefaultRepository} from './default-repository';
 export {Repository} from './repository';
 export {Entity} from './entity';
+export {OrmMetadata} from './orm-metadata';
 export {EntityManager} from './entity-manager';
 export {association} from './decorator/association';
 export {resource} from './decorator/resource';
@@ -14,4 +17,8 @@ export function configure(aurelia, configCallback) {
   let entityManagerInstance = aurelia.container.get(EntityManager);
 
   configCallback(entityManagerInstance);
+
+  ValidationGroup.prototype.hasAssociation = function() {
+    return this.isNotEmpty().passesRule(new HasAssociationValidationRule());
+  };
 }