Cannot mix behaviour and cannot use non registered modifiers

lib/model.js

@@ -7,6 +7,8 @@
 var dateToJSON = function () { return { $$date: this.getTime() }; }
   , originalDateToJSON = Date.prototype.toJSON
   , util = require('util')
+  , _ = require('underscore')
+  , modifierFunctions = {}
   ;
 
 
@@ -123,19 +125,42 @@ function deepCopy (obj) {
 }
 
 
+modifierFunctions.$inc = function () {};
+modifierFunctions.$set = function () {};
+
+
 /**
  * Modify a DB object according to an update query
  * For now the updateQuery only replaces the object
  */
 function modify (obj, updateQuery) {
-  if (updateQuery._id) { throw "You cannot change a document's _id"; }
+  var keys = Object.keys(updateQuery)
+    , firstChars = _.map(keys, function (item) { return item[0]; })
+    , dollarFirstChars = _.filter(firstChars, function (c) { return c === '$'; })
+    , newDoc, modifiers
+    ;
 
-  updateQuery = deepCopy(updateQuery);
+  if (keys.indexOf('_id') !== -1) { throw "You cannot change a document's _id"; }
-  updateQuery._id = obj._id;
 
-  checkObject(updateQuery);
+  if (dollarFirstChars.length !== 0 && dollarFirstChars.length !== firstChars.length) {
+    throw "You cannot mix modifiers and normal fields";
+  }
+
+  if (dollarFirstChars.length === 0) {
+    // Simply replace the object with the update query contents
+    newDoc = deepCopy(updateQuery);
+    newDoc._id = obj._id;
+  } else {
+    // Apply modifiers
+    modifiers = _.uniq(keys);
+    modifiers.forEach(function (m) {
+      if (!modifierFunctions[m]) { throw "Unknown modifier " + m; }
+    });
+  }
 
-  return updateQuery;
+  // Check result is valid and return it
+  checkObject(newDoc);
+  return newDoc;
 };
 
 

test/model.test.js

@@ -212,7 +212,7 @@ describe('Model', function () {
       t._id.should.equal('keepit');
     });
 
-    it('Raise an error if trying to replace the _id field in a copy-type modification', function () {
+    it('Throw an error if trying to replace the _id field in a copy-type modification', function () {
       var obj = { some: 'thing', _id: 'keepit' }
         , updateQuery = { replace: 'done', bloup: [ 1, 8], _id: 'donttryit' }
         ;
@@ -222,6 +222,24 @@ describe('Model', function () {
       }).should.throw();
     });
 
+    it('Throw an error if trying to use modify in a mixed copy+modify way', function () {
+      var obj = { some: 'thing' }
+        , updateQuery = { replace: 'me', $modify: 'metoo' };
+
+      (function () {
+        model.modify(obj, updateQuery);
+      }).should.throw();
+    });
+
+    it('Throw an error if trying to use an inexistent modifier', function () {
+      var obj = { some: 'thing' }
+        , updateQuery = { $set: 'this exists', $modify: 'not this one' };
+
+      (function () {
+        model.modify(obj, updateQuery);
+      }).should.throw();
+    });
+
   });   // ==== End of 'Modifying documents' ==== //
 
 });