From 5bc7333a2a7f7462347550eb9f9d035f97e2c65c Mon Sep 17 00:00:00 2001
From: Casey Foster <c@sey.me>
Date: Mon, 3 Feb 2014 11:49:09 -0600
Subject: [PATCH] Re #2976 Allow `id` values to be generated from a function
 given attrs

---
 backbone.js        | 21 ++++++++++++++-------
 test/collection.js |  5 +++++
 test/model.js      | 15 +++++++++++++++
 3 files changed, 34 insertions(+), 7 deletions(-)

diff --git a/backbone.js b/backbone.js
index 8f68760c4..2808fbe2b 100644
--- a/backbone.js
+++ b/backbone.js
@@ -271,6 +271,12 @@
     // CouchDB users may want to set this to `"_id"`.
     idAttribute: 'id',
 
+    // The function that will generate an id for a model given that model's
+    // attributes.
+    generateId: function (attrs) {
+      return attrs[this.idAttribute];
+    },
+
     // Initialize is an empty function by default. Override it with your own
     // initialization logic.
     initialize: function(){},
@@ -335,9 +341,6 @@
       }
       current = this.attributes, prev = this._previousAttributes;
 
-      // Check for changes of `id`.
-      if (this.idAttribute in attrs) this.id = attrs[this.idAttribute];
-
       // For each `set` attribute, update or delete the current value.
       for (attr in attrs) {
         val = attrs[attr];
@@ -350,6 +353,10 @@
         unset ? delete current[attr] : current[attr] = val;
       }
 
+      var prevId = this.id;
+      this.id = this.generateId(current);
+      if (prevId !== this.id) this.trigger('changeId', this, prevId, options);
+
       // Trigger all relevant attribute changes.
       if (!silent) {
         if (changes.length) this._pending = options;
@@ -552,7 +559,7 @@
 
     // A model is new if it has never been saved to the server, and lacks an id.
     isNew: function() {
-      return !this.has(this.idAttribute);
+      return this.id == null;
     },
 
     // Check if the model is currently in a valid state.
@@ -684,7 +691,7 @@
         if (attrs instanceof Model) {
           id = model = attrs;
         } else {
-          id = attrs[this.model.prototype.idAttribute || 'id'];
+          id = this.model.prototype.generateId(attrs);
         }
 
         // If a duplicate is found, prevent it from being added and
@@ -938,8 +945,8 @@
     _onModelEvent: function(event, model, collection, options) {
       if ((event === 'add' || event === 'remove') && collection !== this) return;
       if (event === 'destroy') this.remove(model, options);
-      if (model && event === 'change:' + model.idAttribute) {
-        delete this._byId[model.previous(model.idAttribute)];
+      if (event === 'changeId') {
+        if (collection != null) delete this._byId[collection];
         if (model.id != null) this._byId[model.id] = model;
       }
       this.trigger.apply(this, arguments);
diff --git a/test/collection.js b/test/collection.js
index 755f6c889..1c5798bb3 100644
--- a/test/collection.js
+++ b/test/collection.js
@@ -1342,4 +1342,9 @@
     strictEqual(collection.models.length, 0);
   });
 
+  test("Models shouldn't be lost by set({id: 1}, {silent: true})", function () {
+    var collection = new Backbone.Collection([{name: 'Curly'}]);
+    collection.first().set({id: 1}, {silent: true});
+    equal(collection.get(1), collection.first());
+  });
 })();
diff --git a/test/model.js b/test/model.js
index 89f01cf0d..0ec0a0a76 100644
--- a/test/model.js
+++ b/test/model.js
@@ -1127,4 +1127,19 @@
     model.set({a: true});
   });
 
+  test("generateId", function() {
+    var Model = Backbone.Model.extend();
+
+    // Simple default uses `idAttribute`
+    equal(Model.prototype.generateId({id: 1}), 1);
+    Model.prototype.idAttribute = '_id';
+    equal(Model.prototype.generateId({_id: 1}), 1);
+
+    // Composite key example
+    Model.prototype.generateId = function (attrs) {
+      return attrs.a + '-' + attrs.b;
+    };
+    equal((new Model({a: 123, b: 456})).id, '123-456');
+  });
+
 })();