PHP: How to make dataprocessor to work with multiselect?

How to make dataprocessor to work with multiselect? Is it possible? I have loaded options in multiselect, but unable to load selected values.
I have many-to-many relation table, with two fields as primary key. In other words - “Item” have a “Category” or few.

>     var categoryForm = categoryWin.attachForm(
>       [{
>         type:"multiselect",
>         connector: "data/tests.categories.php",//-this working fine
>         name: "category",
>       }]
>     ...
>     var dp3 = new dataProcessor("data/tests.category.form.php?id="+myForm.getItemValue('id'))
>     dp3.init(categoryForm);
>     ...
>     This loads one selected value, when there are definitely two must be:
>     //categoryForm.load("data/tests.category.form.php?id="+myForm.getItemValue('id'));
>     ...
>     PHP file:
>     <?php
>     require_once('../dx/connector/form_connector.php');
>     require_once '';
>     $form = new FormConnector($conn);
>     $form->render_table("tests_category","test","category");
>     ...
>     MySql: 
>     CREATE TABLE `tests_category` (
>       `test` int(11) NOT NULL,
>       `category` int(11) NOT NULL
>     ALTER TABLE `tests_category`
>       ADD PRIMARY KEY (`test`,`category`);

you need to use an individual connector object for loading the options for your multiselect (select options connector)
while the dataprocessor should be attached to the dhtmlxForm, not the multiselect and connected to the connector that loads the data to your form fields.

I have try that, and working fine partially - load options. Problem in selected options, I can’t load that, example not shows how, and not find the documentation about php. Example loads only value-label, not selected attribute.

Where I should load “selected” or “checked” in this connector?

Your form saves only the values of the selected options of your multiselect
selectOptions connector only can load all the options to your multiselect. selected options are defined as values in your form connector