add static method to get inherited class querybuilder from model, add isset method in model

tests/DbTest.php

@@ -91,7 +91,21 @@ test("querybuilder", function() {
 
     $qb->reset();
     $rows = $qb->whereNotNull("col1")->get();
-    expect(count($rows))->toBe(2);
+    expect(count($rows))->toBe(2);    
+});
+
+test("extending model",function()
+{
+    $class = "Test";
+    $code = "class $class extends \Kletellier\PdoWrapper\Model {}";
+    eval($code);
+
+    $qbs = Test::q(); 
+    expect($qbs)->toBeInstanceOf(QueryBuilder::class);
+
+    $row = $qbs->find(1);
+    expect($row->id)->toBe(1);
+    expect($row->col1)->toBe("test");
 });
 
 test("order by", function(){
@@ -119,7 +133,18 @@ test("group by", function(){
     expect($rows->first()->Nb)->toBe(1);
 });
 
+test("isset",function()
+{
+    $q = new QueryBuilder("test");
+    $row = $q->where("id",1)->get()->first();
+ 
+    expect($row->id)->toBe(1);
+    expect($row->col1)->toBe("test");
 
+    expect(isset($row->col1))->toBe(true);
+    expect(isset($row->col2))->toBe(false);
+    expect(isset($row->find))->toBe(true);
+});
 
 test("update row", function() {
     $qb = new QueryBuilder("test","id");