Save relationship and grid fields with the Channel Entry Model

public function createEntry(){

    // Channel id of which to create an entry from
    $channel_id = 2;
    // Title is used for the title field and url field
    $title = 'Entry Title 15';
   
    // Some basic entry stuff
    $entry = ee('Model')->make('ChannelEntry');
    $entry->channel_id = $channel_id;
    $entry->site_id =  ee()->config->item('site_id');
    $entry->author_id = ee()->session->userdata('member_id');
    $entry->ip_address = ee()->session->userdata('ip_address');
    $entry->status = "open";
    $entry->sticky = FALSE;
    $entry->title = $title;
    $entry->url_title = ee('Format')->make('Text', $title)->urlSlug()->compile();
    $entry->entry_date = ee()->localize->now;
    $entry->edit_date = ee()->localize->now;

    // Now the good stuff
    // -------------------------------
    // Save a custom fields
    $text_input_field_id = 2; // This is the id of the custom text fieldtype
    $entry->{'field_id_' . $text_input_field_id} = 'Custom text field!';
    
    // Save a relationship field
    $relationship_field_id = 8; // This is the id of the custom relationship fieldtype
    // Array of entry_id's to relate to in the relationship field multiple would be [1,2]
    $ids = [1];
    $entry->{'field_id_'. $relationship_field_id} = array('data' => $ids);
    
    // Save a Grid field
    // This is the id of the custom grid fieldtype
    $grid_field_id = 9;
    // I have 3 fields inside the grid: a relationship, number and text field
    // The col_id's for the fieldtype can be found inside the grid_columns table
    $grid_values = [
      'col_id_7' => array('data' => $ids),
      'col_id_8' => 9001,
      'col_id_9' => 'Custom Field is set!'
    ]; 
    // To save a new grid row you use new_row_{ROW_ID}
    $entry->{'field_id_' . $grid_field_id} = array(
      'new_row_0' => $grid_values, 
      'new_row_1' => $grid_values
    );
    // -------------------------------

    // Validate and Save.
    $result = $entry->validate();

    if ($result->isValid()) {
      // Valid-> Save the entry
      $entry->save();
    } else {
      // Probably invalid
    }
  }

// Get the entry object.
$entry_id = 3;
$entry = ee('Model')->get('ChannelEntry', $entry_id)->first();

// Save a relationship field
$relationship_field_id = 8; // This is the id of the custom relationship fieldtype
// Array of entry_id's to relate to in the relationship field multiple would be [1,2]
// the index of the array would probably determine the order but i haven't tested it
$ids = [1,2,3,4,5,6];
$entry->{'field_id_'. $relationship_field_id} = array('data' => $ids);

// Validate and Save.
$result = $entry->validate();

if ($result->isValid())
{
  $entry->save();
}