Added pre-save validation for unique indexes

lib/model.js

@@ -2372,13 +2372,48 @@ Model.compile = function compile (name, schema, collectionName, connection, base
   // apply named scopes
   if (schema.namedScopes) schema.namedScopes.compile(model);
 
+  // apply validation for paths with a unique index
+  for(var path in schema.paths) {
+    applyUniqueIndexValidation(model, schema, path);
+  };
+
   model.schema = model.prototype.schema;
   model.options = model.prototype.options;
   model.collection = model.prototype.collection;
 
   return model;
 };
 
+/**
+ * Adds validation for the path if its SchemaType indicates that it has a unique index.
+ *
+ * The validator checks to see if the collection already contains a document with the path’s value and throws an error
+ * if it does
+ *
+ * @param {Model} model
+ * @param {Schema} schema
+ * @param {String} path
+ * @api private
+ */
+function applyUniqueIndexValidation (model, schema, path) {
+  var schemaType = schema.paths[path];
+  if (schemaType._index && schemaType._index.unique) {
+    schemaType.validate(__checkUnique, 'duplicate');
+  }
+
+  function __checkUnique (value, respond) {
+    var conditions = {};
+    conditions[path] = value;
+    model.findOne(conditions, function (err, document) {
+      if (!document) {
+        respond(true);
+      } else {
+        respond(false);
+      }
+    });
+  }
+}
+
 /*!
  * Subclass this model with `conn`, `schema`, and `collection` settings.
  *

test/model.test.js

@@ -1499,6 +1499,27 @@ describe('Model', function(){
         });
       })
     })
+
+    describe('unique fields', function () {
+      it ('are validated before save', function (done) {
+        var db = start();
+        var uniqueSchema = new Schema({ uniqueField: { type: String, unique: true }, normalField: {type: String }});
+        var UniqueObject = db.model('UniqueObject', uniqueSchema);
+
+        new UniqueObject({ uniqueField: 'foo', normalField: 'bar' }).save(function (err) {
+          assert.strictEqual(null, err);
+          new UniqueObject({ uniqueField: 'foo', normalField: 'bar' }).save(function (err) {
+            assert.strictEqual('duplicate', err.errors.uniqueField.type);
+            assert.strictEqual('uniqueField', err.errors.uniqueField.path);
+            assert.strictEqual('foo', err.errors.uniqueField.value);
+            assert.strictEqual('undefined', typeof err.errors.normalField);
+
+            db.close();
+            done();
+          });
+        });
+      });
+    });
   });
 
   describe('defaults application', function(){