snippet.php

<?php
// import a pipe delimited list of entry ids into your custom field
// this is the column name of your Playa field
$ee_column = 'field_id_160';

global $DB;
$rels = array();

$entries_query = $DB->query("SELECT entry_id, $ee_column FROM exp_weblog_data WHERE $ee_column");
$entries = $entries_query->result;

foreach ($entries as $entry) :

  $entry_id = $entry['entry_id'];
  $split_rels = explode('|', $entry[$ee_column]);
  
  foreach ($split_rels as $rel) :
    $rels[] = array(
      'rel_parent_id' => $entry_id,
      'rel_child_id' => $rel,
      'rel_type'  => 'blog',
    );
  endforeach;
  
  // clear field
  $clear_field = $DB->update_string('exp_weblog_data', array($ee_column => ''), "entry_id = $entry_id" );
  $DB->query($clear_field);
  
endforeach;

foreach ($rels as $rel) :
  
  $entry_id = $rel['rel_parent_id'];
  
  // update rel table, get rel id
  $insert = $DB->insert_string('exp_relationships', $rel);
  $DB->query($insert);
  $rel_id = $DB->insert_id;
  echo "Inserted $rel_id in exp_relationships\n";
  
  // find current value
  $select = $DB->query("SELECT $ee_column FROM exp_weblog_data WHERE entry_id = $entry_id");
  $current = $select->row[$ee_column];
  
  // update weblog data
  $data = array(
    $ee_column  =>  $current . "[" . $rel_id . "]\n"
  );
  $update = $DB->update_string('exp_weblog_data', $data, "entry_id = $entry_id" );
  $DB->query($update);
  echo "Updated entry $entry_id in exp_weblog_data\n\n";
  
endforeach;

?>