Formit save data in database table

<?php

/* Add ah_postings package */

$path = MODX_CORE_PATH . 'components/ah_postings/';
$result = $modx->addPackage('ah_postings',$path . 'model/','vw_ah_pos_');

/* Create new posting object */

$position = $modx -> newObject('Postings');

if (!is_object($position) || !($position instanceof xPDOObject)) {
    $errorMsg='Failed to create object of type:Postings ';
    $hook->addError('error_message',$errorMsg); 
    return false;
}

return true;

&hooks = `snippetname,email`

[[!+fi.error_message:notempty=`<div id="update-message">[[!+fi.error_message]]</div>`]]
[[!+fi.successMessage:notempty=`<div id="update-message">[[!+fi.successMessage]]</div>`]]

<?php

/* Add ah_postings package and throw an error if unsuccessful */
$path = MODX_CORE_PATH . 'components/ah_postings/';
$result = $modx->addPackage('ah_postings',$path . 'model/','vw_ah_pos_');

if (! $result) {
  $errorMsg='Failed to add package ';
  $hook->addError('error_message',$errorMsg); 
  return false;
}

/* Create new posting object & check if object was created or else throw an error */
$position = $modx -> newObject('Postings');

if (!is_object($position) || !($position instanceof xPDOObject)) {
    $errorMsg='Failed to create object of type:Postings ';
    $hook->addError('error_message',$errorMsg); 
    return false;
}

/* Set data from form */

$position->set('usr', $_POST['usr']);

/* Save data from form and throw out errors if fails */

if (!$position->save()) {
    $errorMsg='Failed to save object ';
    $hook->addError('error_message',$errorMsg); 
    return false;
}
else
    return true;

Placeholder in form: [[fi.usr]]
Database field name: usr

<?php
$xpdo_meta_map['Postings']= array (
  'package' => 'ah_postings',
  'version' => '1.1',
  'table' => 'postings',
  'fields' => 
  array (
    'id' => NULL,
    'usr' => NULL,
    'department' => NULL,
    'duration' => NULL,
    'renumeration' => NULL,
    'apply-method' => NULL,
    'interns' => NULL,
    'date' => NULL,
  ),
  'fieldMeta' => 
  array (
    'id' => 
    array (
      'dbtype' => 'int',
      'precision' => '10',
      'attributes' => 'unsigned',
      'phptype' => 'integer',
      'null' => false,
      'index' => 'pk',
    ),
    'usr' => 
    array (
      'dbtype' => 'int',
      'precision' => '10',
      'attributes' => 'unsigned',
      'phptype' => 'integer',
      'null' => false,
    ),
    'department' => 
    array (
      'dbtype' => 'varchar',
      'precision' => '255',
      'phptype' => 'string',
      'null' => false,
    ),
    'duration' => 
    array (
      'dbtype' => 'int',
      'precision' => '10',
      'attributes' => 'unsigned',
      'phptype' => 'integer',
      'null' => false,
    ),
    'renumeration' => 
    array (
      'dbtype' => 'int',
      'precision' => '1',
      'attributes' => 'unsigned',
      'phptype' => 'integer',
      'null' => false,
    ),
    'apply-method' => 
    array (
      'dbtype' => 'int',
      'precision' => '1',
      'attributes' => 'unsigned',
      'phptype' => 'integer',
      'null' => false,
    ),
    'interns' => 
    array (
      'dbtype' => 'int',
      'precision' => '100',
      'phptype' => 'integer',
      'null' => false,
    ),
    'date' => 
    array (
      'dbtype' => 'varchar',
      'precision' => '10',
      'phptype' => 'string',
      'null' => false,
    ),
  ),
  'indexes' => 
  array (
    'PRIMARY' => 
    array (
      'alias' => 'PRIMARY',
      'primary' => true,
      'unique' => true,
      'type' => 'BTREE',
      'columns' => 
      array (
        'id' => 
        array (
          'length' => '',
          'collation' => 'A',
          'null' => false,
        ),
      ),
    ),
  ),
);

$position -> set('usr', $_POST['fi.usr']);

$position -> set('id', '999');