Use the primary key type for the generated foreign key

lib/datasource.js

@@ -1430,11 +1430,19 @@ DataSource.prototype.defineForeignKey = function defineForeignKey(className, key
     // quit if key already defined
     if (this.getModelDefinition(className).rawProperties[key]) return;
 
+    var defaultType = Number;
+    if(foreignClassName) {
+      var foreignModel = this.getModelDefinition(foreignClassName);
+      var pkName = foreignModel && foreignModel.idName();
+      if(pkName) {
+        defaultType = foreignModel.properties[pkName].type;
+      }
+    }
     if (this.connector.defineForeignKey) {
         var cb = function (err, keyType) {
             if (err) throw err;
             // Add the foreign key property to the data source _models
-            this.defineProperty(className, key, {type: keyType || Number});
+            this.defineProperty(className, key, {type: keyType || defaultType});
         }.bind(this);
         switch (this.connector.defineForeignKey.length) {
             case 4:
@@ -1447,7 +1455,7 @@ DataSource.prototype.defineForeignKey = function defineForeignKey(className, key
         }
     } else {
         // Add the foreign key property to the data source _models
-        this.defineProperty(className, key, {type: Number});
+        this.defineProperty(className, key, {type: defaultType});
     }
 
 };

test/loopback-dl.test.js

@@ -510,6 +510,19 @@ describe('Load models with relations', function () {
         done();
     });
 
+    it('should set up foreign key with the correct type', function (done) {
+        var ds = new DataSource('memory');
+
+        var User = ds.define('User', {name: String, id: {type: String, id: true}});
+        var Post = ds.define('Post', {content: String}, {relations: {user: {type: 'belongsTo', model: 'User'}}});
+
+        var fk = Post.definition.properties['userId'];
+        assert(fk, 'The foreign key should be added');
+        assert(fk.type === String, 'The foreign key should be the same type as primary key');
+        assert(Post.relations['user'], 'User relation should be set');
+        done();
+    });
+
     it('should set up hasMany and belongsTo relations', function (done) {
         var ds = new DataSource('memory');