How to update field values of a content type's nodes when when viewing a particular content type page

Question

I'd essentially like to alter the values of a specific custom field of a few of nodes before they're displayed in a view on the 'page' of a specific content type.

The content type is that will be displayed is a park. When a park is viewed, one of the blocks shown is a view that fetches and shows several nodes that are also 'parks'.

This park content type has a field called proximity. I'd like to change the value of proximity (based on a mathematical formula) for all parks before the view is processed, so that I can use proximity in the view.

From what I understand so far, I should use a park_preprocess function, which calls some sort of hook to change the proximity values. Is this correct, and how would I do it?

Answer 1

hook_node_view() will be used in this scenario.

function hook_node_view($node, $view_mode, $langcode) {
  if($node->type == 'park' && $view_mode == 'full')
   {
    /* change the value of proximity here after applying your formula. 
      * Here you have complete node array, so you alter the result easily here.
    */

   }
 }

Answer 2

you can use hook_node_view as @Pushpinder Rana said.but if you want to modify a field you should save your node.here i simply plus one my proximity field on my hook.

/**
 * Impelement hook_node_view
 * @param type $node
 * @param type $view_mode
 * @param type $langcode
 */
function MODULENAME_node_view($node, $view_mode, $langcode) {
    //plus one proximity field and save a node
    $new_value = $node->field_proximity[LANGUAGE_NONE][0]['value'] + 1;
    $node->field_proximity[LANGUAGE_NONE][0]['value'] = $new_value;
    node_submit($node);
    node_save($node);
    // here is to show user updated proximity value;    
    $node->content['field_proximity'][0]['#markup'] = $new_value;
    }

Answer 3

Thanks to Pushinder and Shirin for responding, and providing the start I needed! However both answers were lacking the detail I needed. I won't paste my entire code here, as it's too long, but I'll describe what I used and why:

• hook_node_view was the right hook to call my function at the right time - before page load
• $refN = $node->field_location_n[LANGUAGE_NONE][0]['value']; and the same for East were required to get the reference coordinates
• Because I have several hundred nodes with coordinates, I couldn't load each one individually using load_node or collectively using load_node_multiple since this used far too many resources for every page load
• Instead, I used db_query and field_attach_load together, as described in this answer: https://drupal.stackexchange.com/a/30906/20264 to effectively load just the values I needed
• I then used foreach( $nodes as $nodei ) { to loop through all the results
• $distance = sqrt( pow( $refN - $nodeiN, 2 ) + pow( $refE - $nodeiE, 2 ) ); was my proximity calculation
• Then, only for results with a specified proximity would I update $node

• Since I was using the Entity Reference module to record 'Nearby places' in my nodes, I used the following to update the entity references:

  $node->field_nearby[LANGUAGE_NONE][$i] = array( "target_id" => $nodei->nid );