Fixes in belongsTo relation definition syntax

lib/model.js

@@ -512,6 +512,12 @@ AbstractClass.include = function (objects, include, cb) {
         }
         var relation = relations[relationName];
 
+        if (!relation) {
+            return function() {
+                cb(new Error('Relation "' + relationName + '" is not defined for ' + self.modelName + ' model'));
+            }
+        }
+
         var req = {'where': {}};
 
         if (!keyVals[relation.keyFrom]) {
@@ -957,10 +963,14 @@ AbstractClass.belongsTo = function (anotherClass, params) {
     params = params || {};
     if ('string' === typeof anotherClass) {
         params.as = anotherClass;
-        var anotherClassName = anotherClass.toLowerCase();
+        if (params.model) {
-        for(var name in this.schema.models) {
+            anotherClass = params.model;
-            if (name.toLowerCase() === anotherClassName) {
+        } else {
-                anotherClass = this.schema.models[name];
+            var anotherClassName = anotherClass.toLowerCase();
+            for(var name in this.schema.models) {
+                if (name.toLowerCase() === anotherClassName) {
+                    anotherClass = this.schema.models[name];
+                }
             }
         }
     }
@@ -969,7 +979,7 @@ AbstractClass.belongsTo = function (anotherClass, params) {
 
     this.relations[params['as']] = {
         type: 'belongsTo',
-        keyFrom: params['foreignKey'],
+        keyFrom: fk,
         keyTo: 'id',
         modelTo: anotherClass,
         multiple: false