How to set up a prefilter for a Participants Database Participant Log list display

pdb-log-list-prefilter.php

<?php
/**
 * Plugin Name: PDB Log List Prefilter
 * Description: filters which log entries are presented in a log list
 *
 * @see https://gist.github.com/xnau/856b362ccdd7545cdfd02dbbb83b273e
 */
if ( !class_exists( 'xnau_filtered_log_template' ) ):
  
class xnau_filtered_log_template 
{
  // name of the log that we will be filtering
  private $log_name = 'work_log';

  // name of the log entry field we are filtering by
  private $filter_field = 'work_log_completion';

  /* 
   * this is the comparison operator we will use
   * 
   * this can be one of: 'equals', 'not equals', 'greater than', 'less than'
   *
   * if you use greater than or less than, your comparison value must be numeric, 
   * these operators won't work with string values! 
   */
  private $operator = 'equals';

  /*
   * this is the comparison value we will use
   * 
   * this can be a number or a string
   */
  private $check_value = 0;

  // don't edit the stuff below here
  
  /**
   * @var bool true if the filter should be applied
   * 
   * this is to make sure it's only applied where the special template is used
   */
  private $set_filter = false;

  public function __construct()
  {
    add_filter( 'pdb-shortcode_call_pdb_record', [$this,'check_shortcode'] );
    add_filter( 'pdb-shortcode_call_pdb_single', [$this,'check_shortcode'] );
    
    // determine the operator
    switch ( $this->operator ) 
    {
      case 'not equals':
        $this->operator = '<>';
        break;
      case 'less than':
        $this->operator = '<';
        break;
      case 'greater than':
        $this->operator = '>';
        break;
      case 'equals':
      default:
        $this->operator = '=';
    }

    // this sets up the function that will alter the database query for the log
    add_filter( "pdblog-{$this->log_name}_record_entries_query", [ $this, 'alter_log_query' ] );
  }
  
  /**
   * @param array $shortcode_attributes
   * @return array attributes
   */
  public function check_shortcode( $shortcode_attributes )
  {
    if ( isset( $shortcode_attributes['prefilter'] ) )
    {
      $this->set_filter = true;
    }
    
    return $shortcode_attributes;
  }

  /*
   * adds the filtering clause to the query
   * 
   * @global \wpdb $wpdb
   * @param string $query
   * @return string query
   */
  public function alter_log_query( $query )
  {
    if ( ! $this->set_filter )
    {
      // if the filter is not enabled, return the unaltered query
      return $query;
    }
    
    global $wpdb;
    
    /*
     * this builds the filter clause we will add
     * the $wpdb->prepare() method makes sure the resulting query is valid and safe
     */
    $filter_clause = $wpdb->prepare( 'WHERE %i ' . $this->operator . ' %s AND ', $this->filter_field, $this->check_value );
    
    $altered_query = str_replace( 'WHERE', $filter_clause, $query );
    
    return $altered_query;
  }
}


endif;

new xnau_filtered_log_template;

If you are a coder, there are all kinds of things you can do with this (like complex filtering on multiple field values) once you understand how it works.