Add a relation example following Ruby on Rails active records

examples/relations.js

@@ -0,0 +1,90 @@
+var DataSource = require('../index').DataSource;
+var ds = new DataSource('memory');
+
+var Order = ds.createModel('Order', {
+    customerId: Number,
+    orderDate: Date
+});
+
+var Customer = ds.createModel('Customer', {
+    name: String
+});
+
+Order.belongsTo(Customer);
+
+Customer.create({name: 'John'}, function (err, customer) {
+    Order.create({customerId: customer.id, orderDate: new Date()}, function (err, order) {
+        order.customer(console.log);
+        order.customer(true, console.log);
+
+        Customer.create({name: 'Mary'}, function (err, customer2) {
+            order.customer(customer2);
+            order.customer(console.log);
+        });
+    });
+});
+
+
+Customer.hasMany(Order, {as: 'orders', foreignKey: 'customerId'});
+
+Customer.create({name: 'Ray'}, function (err, customer) {
+    Order.create({customerId: customer.id, orderDate: new Date()}, function (err, order) {
+        customer.orders(console.log);
+        customer.orders.create({orderDate: new Date()}, console.log);
+        customer.orders.findById('2', console.log);
+        customer.orders.destroy('2', console.log);
+    });
+});
+
+
+var Physician = ds.createModel('Physician', {
+    name: String
+});
+
+var Patient = ds.createModel('Patient', {
+    name: String
+});
+
+var Appointment = ds.createModel('Appointment', {
+    physicianId: Number,
+    patientId: Number,
+    appointmentDate: Date
+});
+
+Appointment.belongsTo(Patient);
+Appointment.belongsTo(Physician);
+
+Physician.hasMany(Patient, {through: Appointment});
+Patient.hasMany(Physician, {through: Appointment});
+
+Physician.create({name: 'Smith'}, function (err, physician) {
+    Patient.create({name: 'Mary'}, function (err, patient) {
+        Appointment.create({appointmentDate: new Date(), physicianId: physician.id, patientId: patient.id},
+            function (err, appt) {
+                physician.patients(console.log);
+                patient.physicians(console.log);
+        });
+    });
+});
+
+
+var Assembly = ds.createModel('Assembly', {
+    name: String
+});
+
+var Part = ds.createModel('Part', {
+    partNumber: String
+});
+
+Assembly.hasAndBelongsToMany(Part);
+Part.hasAndBelongsToMany(Assembly);
+
+Assembly.create({name: 'car'}, function (err, assembly) {
+    Part.create({partNumber: 'engine'}, function (err, part) {
+        assembly.parts.add(part, function(err) {
+            assembly.parts(console.log);
+        });
+
+    });
+});
+

lib/relations.js

@@ -140,12 +140,14 @@ Relation.hasMany = function hasMany(anotherClass, params) {
     }
 
     function destroy(id, cb) {
-        this.findById(id, function (err, inst) {
+        var self = this;
+        anotherClass.findById(id, function (err, inst) {
             if (err) return cb(err);
-            if (inst) {
+            if (!inst) return cb(new Error('Not found'));
+            if (inst[fk] && inst[fk].toString() == self.id.toString()) {
                 inst.destroy(cb);
             } else {
-                cb(new Error('Not found'));
+                cb(new Error('Permission denied'));
             }
         });
     }