atk4\data\Model::set PHP Method

    public function set($field, $value = null)
    {
        if (func_num_args() == 1) {
            if (is_array($field)) {
                foreach ($field as $key => $value) {
                    if ($key === '0' || $key === 0) {
                        $this->set($value);
                    } else {
                        $this->set($key, $value);
                    }
                }
                return $this;
            } else {
                $value = $field;
                $field = $this->title_field;
            }
        }
        $field = $this->normalizeFieldName($field);
        $f = $this->hasElement($field);
        try {
            if ($f && $this->hook('normalize', [$f, $value]) !== false) {
                $value = $f->normalize($value);
            }
        } catch (Exception $e) {
            $e->addMoreInfo('field', $field);
            $e->addMoreInfo('value', $value);
            $e->addMoreInfo('f', $f);
            throw $e;
        }
        $default_value = $f ? $f->default : null;
        $original_value = array_key_exists($field, $this->dirty) ? $this->dirty[$field] : (isset($f) && isset($f->default) ? $f->default : null);
        $current_value = array_key_exists($field, $this->data) ? $this->data[$field] : $original_value;
        if (gettype($value) == gettype($current_value) && $value == $current_value) {
            // do nothing, value unchanged
            return $this;
        }
        if ($f) {
            // perform bunch of standard validation here. This can be re-factored in the future.
            if ($f->read_only) {
                throw new Exception(['Attempting to change read-only field', 'field' => $field, 'model' => $this]);
            }
            if ($f->enum && $f->type != 'boolean') {
                if ($value === '') {
                    $value = null;
                }
                if (!in_array($value, $f->enum, true) && $value !== null) {
                    throw new Exception(['This is not one of the allowed values for the field', 'field' => $field, 'model' => $this, 'value' => $value, 'enum' => $f->enum]);
                }
            }
        }
        if (array_key_exists($field, $this->dirty) && (gettype($this->dirty[$field]) == gettype($value) && $this->dirty[$field] == $value)) {
            unset($this->dirty[$field]);
        } elseif (!array_key_exists($field, $this->dirty)) {
            $this->dirty[$field] = array_key_exists($field, $this->data) ? $this->data[$field] : $default_value;
        }
        $this->data[$field] = $value;
        return $this;
    }

 public function testUpdateArray()
 {
     $a = ['user' => [1 => ['name' => 'John', 'surname' => 'Smith'], 2 => ['name' => 'Sarah', 'surname' => 'Jones']]];
     $p = new Persistence_Array($a);
     $m = new Model($p, 'user');
     $m->addField('name');
     $m->addField('surname');
     $m->load(1);
     $m['name'] = 'Peter';
     $m->save();
     $m->load(2);
     $m['surname'] = 'Smith';
     $m->save();
     $m['surname'] = 'QQ';
     $m->save();
     $this->assertEquals(['user' => [1 => ['name' => 'Peter', 'surname' => 'Smith'], 2 => ['name' => 'Sarah', 'surname' => 'QQ']]], $a);
     $m->unload();
     $m->set(['name' => 'Foo', 'surname' => 'Bar']);
     $m->save();
     $this->assertEquals(['user' => [1 => ['name' => 'Peter', 'surname' => 'Smith'], 2 => ['name' => 'Sarah', 'surname' => 'QQ'], 3 => ['name' => 'Foo', 'surname' => 'Bar', 'id' => 3]]], $a);
 }