Using Rules to create an Entity Reference if two fields in different entities match?

Question

I'm attempting to use a "registration code" entered during a user's registration to create an entity reference to a node with a corresponding code.

Any help is greatly appreciated.

Specific use case:

"Professor" (users) have "Classes" (nodes) that contain a text-field with a unique 5-digit code (created with Computed Field).

"Students" have a "Registration Code" field on their registration & user profile page (aka a text field on the user entity) for manually entering a 5-digit code that should "assign" them to a "Class" that has the same registration code.

I'm not a programmer, but this might make more sense:

if [Student user's 5-digit registration code] = ["Class" node's 5-digit registration code] then an entity reference is created between [student user] and ["class" node]

I'd like the rule to trigger when a user updates the registration code field.

Essentially, I'm attempting to avoid displaying Entity Reference's autocomplete widget to users.

Answer 1

I don't think I would start with Rules, especially from a performance standpoint. I would first try something like this:

• in the Student content type, create an Entity Reference field for the reference, making sure it has a default value, say 0 for ease of access later
• Using Field Permissions, hide that field to everyone but admin

The Field Permissions module allows site administrators to set field-level permissions to edit, view and create fields on any entity.

• create a custom module

• using hook_node_validate(), check the list of Classes for the existence of the correct code

• using hook_node_presave(), update the hidden reference field once it is validated

Now you have something that allows the Student to enter a value, have it validated, and then copy that value into a proper reference field for later use

EDIT

I was curious if I was correct in my initial answer, so I figured it out to check, and it worked - for this example:

• Create a content type Class, using the title field as the Class Code

• Create a content type Student

• Add field to Student content type: field_student_class_code, entity reference to Class content type

• use Field Permissions to hide field_student_class_code to everyone but Admin

• Add field to Student content type: field_student_visible_class_code, text field

• Create a new module called custom_node_reference, and include this code:

  function custom_node_reference_node_validate($node, $form, &$form_state)
  {
    if($node->type == 'student')
    {
      $lang = $form['field_student_visible_class_code']['#language'];
      $class_value = check_plain($form['field_student_visible_class_code'][$lang][0]['value']['#value']);
  
      $result = db_select('node', 'table_alias')
          ->condition('type', 'class', '=')
          ->condition('title', $class_value, '=')
          ->fields('table_alias')
          ->execute();
  
      if($result->rowCount() <= 0) 
      {
        form_set_error('field_student_visible_class_code', 'That class code does not exist, please re-enter a valid class code');
      }
    }
  }
  
  
  
  function custom_node_reference_node_presave($node)
  {
    if($node->type == 'student')
    {
      $lang = $node->language;
  
      // get entity_id for current class code
      $val = db_select('node', 'n')
        ->fields('n', array('nid'))
        ->condition('type', 'class', '=')
        ->condition('title', $node->field_student_visible_class_code[$lang][0]['value'], '=')
        ->execute()
        ->fetchField();   
  
        $node->field_student_class_code[$lang][0]['target_id'] = $val;
      }
    }
  

If you change the machine names of the fields, you will need to adjust the code to suit