Add a mixin for saving a subset of a model.

Closes #3403
- Add SelectiveSaveMixin so that a DS.Model can save one or more
  properties at a time while preserving other outstanding changes.

ghost/admin/controllers/modals/transfer-owner.js

@@ -1,10 +1,11 @@
 var TransferOwnerController = Ember.Controller.extend({
-
     actions: {
         confirmAccept: function () {
             var user = this.get('model'),
                 self = this;
 
+            self.get('popover').closePopovers();
+
             // Get owner role
             this.store.find('role').then(function (result) {
                 return result.findBy('name', 'Owner');
@@ -12,16 +13,16 @@ var TransferOwnerController = Ember.Controller.extend({
                 // remove roles and assign owner role
                 user.get('roles').clear();
                 user.get('roles').pushObject(ownerRole);
-                return user.save({ format: false });
-            }).then(function (model) {
+
+                return user.saveOnly('roles');
+            }).then(function () {
                 self.notifications.closePassive();
-                self.notifications.showSuccess('Settings successfully saved.');
-                return model;
+                self.notifications.showSuccess('Ownership successfully transferred to ' + user.get('name'));
             }).catch(function (errors) {
                 self.notifications.closePassive();
+
+                errors = Ember.isArray(errors) ? errors : Ember.A([errors]);
                 self.notifications.showErrors(errors);
-            }).finally(function () {
-                self.get('popover').closePopovers();
             });
         },
 

ghost/admin/mixins/selective-save.js

@@ -0,0 +1,121 @@
+// SelectiveSaveMixin adds a saveOnly method to a DS.Model.
+//
+// saveOnly provides a way to save one or more properties of a model while
+// preserving outstanding changes to other properties.
+var SelectiveSaveMixin = Ember.Mixin.create({
+    saveOnly: function () {
+        if (arguments.length === 0) {
+            return Ember.RSVP.resolve();
+        }
+
+        if (arguments.length === 1 && Ember.isArray(arguments[0])) {
+            return this.saveOnly.apply(this, Array.prototype.slice.call(arguments[0]));
+        }
+
+        var propertiesToSave = Array.prototype.slice.call(arguments),
+            changed,
+            hasMany = {},
+            belongsTo = {},
+            self = this;
+
+        changed = this.changedAttributes();
+
+        // disable observers so we can make changes to the model but not have
+        // them reflected by the UI
+        this.beginPropertyChanges();
+
+        // make a copy of any relations the model may have so they can
+        // be reapplied later
+        this.eachRelationship(function (name, meta) {
+            if (meta.kind === 'hasMany') {
+                hasMany[name] = self.get(name).slice();
+                return;
+            }
+
+            if (meta.kind === 'belongsTo') {
+                belongsTo[name] = self.get(name);
+                return;
+            }
+        });
+
+        try {
+            // roll back all changes to the model and then reapply only those that
+            // are part of the saveOnly
+
+            self.rollback();
+
+            propertiesToSave.forEach(function (name) {
+                if (hasMany.hasOwnProperty(name)) {
+                    self.get(name).clear();
+
+                    hasMany[name].forEach(function (relatedType) {
+                        self.get(name).pushObject(relatedType);
+                    });
+
+                    return;
+                }
+
+                if (belongsTo.hasOwnProperty(name)) {
+                    return self.updateBelongsTo(name, belongsTo[name]);
+                }
+
+                if (changed.hasOwnProperty(name)) {
+                    return self.set(name, changed[name][1]);
+                }
+            });
+        }
+        catch (err) {
+            // if we were not able to get the model into the correct state
+            // put it back the way we found it and return a rejected promise
+
+            Ember.keys(changed).forEach(function (name) {
+                self.set(name, changed[name][1]);
+            });
+
+            Ember.keys(hasMany).forEach(function (name) {
+                self.updateHasMany(name, hasMany[name]);
+            });
+
+            Ember.keys(belongsTo).forEach(function (name) {
+                self.updateBelongsTo(name, belongsTo[name]);
+            });
+
+            self.endPropertyChanges();
+
+            return Ember.RSVP.reject(new Error(err.message || 'Error during saveOnly. Changes NOT saved.'));
+        }
+
+        return this.save().finally(function () {
+            // reapply any changes that were not part of the save
+
+            Ember.keys(changed).forEach(function (name) {
+                if (propertiesToSave.hasOwnProperty(name)) {
+                    return;
+                }
+
+                self.set(name, changed[name][1]);
+            });
+
+            Ember.keys(hasMany).forEach(function (name) {
+                if (propertiesToSave.hasOwnProperty(name)) {
+                    return;
+                }
+
+                self.updateHasMany(name, hasMany[name]);
+            });
+
+            Ember.keys(belongsTo).forEach(function (name) {
+                if (propertiesToSave.hasOwnProperty(name)) {
+                    return;
+                }
+
+                self.updateBelongsTo(name, belongsTo[name]);
+            });
+
+            // signal that we're finished and normal model observation may continue
+            self.endPropertyChanges();
+        });
+    }
+});
+
+export default SelectiveSaveMixin;

ghost/admin/models/user.js

@@ -1,7 +1,8 @@
 import ValidationEngine from 'ghost/mixins/validation-engine';
 import NProgressSaveMixin from 'ghost/mixins/nprogress-save';
+import SelectiveSaveMixin from 'ghost/mixins/selective-save';
 
-var User = DS.Model.extend(NProgressSaveMixin, ValidationEngine, {
+var User = DS.Model.extend(NProgressSaveMixin, SelectiveSaveMixin, ValidationEngine, {
     validationType: 'user',
 
     uuid: DS.attr('string'),