Having a JSON file, how can we set up WordPress to redirect the urls (if it's found in the JSON file)?

For example:

  "foo": "bar",
  "foo-1": "baz"

Then /foo will redirect to /bar and /foo-1 to /baz.

What's the best way to do this? Currently I do it with rewrite_rule in functions.php, but each time the redirects change, I have to save the Permalinks Settings.

The redirects in functions.php are handled like this:

function handle_book_redirects() {
add_action( 'init', 'handle_book_redirects' );

Then if myVar is appended and it's a redirect, a custom php will handle that request.

  • why json make any difference? what is you code that you use to redirect? Jul 12, 2016 at 5:40
  • WordPress use a cache to save ressources when doing the URL Rewriting. then you need to flush the permalinks every time the redirections change
    – mmm
    Jul 12, 2016 at 6:16
  • @mmm How can I trigger the flush from another separated app (which generates the redirects json file)? Jul 12, 2016 at 11:36
  • @MarkKaplun Because I want to make it dynamic. Currently I have to add the redirect urls in two places: in my php file and in functions.php (added in the question). Jul 12, 2016 at 11:37

1 Answer 1


The way I do it. Note there may be a more straightforward way.

Step 1

Add a custom query_varlike this to record the redirect from/to variables

function my_custom_query_vars($vars){
     //this allows you to store custom variables with rediect_from and rediect_to in the url
     $vars[] = 'redirect_from';
     $vars[] = 'redirect_to';
    return $vars;
add_filter( 'query_vars', 'my_custom_query_vars' );

Step 2

Add foreach loop that does something like this. This will add the rewrite rules to change http://example.com/foo to http://example.com/?redirect_from=foo&redirect_to=bar

function my_custom_rewrite_rules($wp_rewrite){
    $new_rules = array();
    $json = '';//get your json data and store it as this string
    $json_array = json_decode($json, true);
    foreach($json_array as $key => $value){
        $new_rules['^'.$key.'$'] = 'index.php/?redirect_from='.$key.'&redirect_to='.$value;
    $wp_rewrite->rules = $new_rules + $wp_rewrite->rules;
add_action('generate_rewrite_rules', 'my_custom_rewrite_rules');

Step 3

Hook into the parse_request filter to parse your request and redirect as necessary.

 function my_custom_parse_request($wp){
//we make sure the keys are present and not empty before we redirect
if ((array_key_exists('redirect_from', $wp->query_vars) 
    && !empty($wp->query_vars['redirect_from']))
    && (array_key_exists('redirect_to', $wp->query_vars)
    && !empty($wp->query_vars['redirect_to']))){
add_action('parse_request', 'my_custom_parse_request');
  • What happens when the JSON file is changed? How can I do it that will trigger an event and will reload the json string? I don't want to read the json file and parse it on every request, but load it in memory and reload it when it's changed. Jul 13, 2016 at 9:22
  • I'd suggest you save the json string as an option in the wp_options table using the optionsAPI. You would then load the json string in the function using get_optiom(). All you'll have to do is update the settings whenever the json file changes. If the json file is not external, you could add a custom hook to re-save the function whenever it changes Jul 13, 2016 at 9:29
  • Is my_custom_rewrite_rules called when flushing the permalinks? I think I will use the WP_Rewrite::wp_rewrite_rules() method to reload the json. Jul 13, 2016 at 9:34
  • The code I gave should be put either in the functions.php of your child theme or in a plugin. I have been using the method in a couple sites and it works flawlessly Jul 13, 2016 at 9:43
  • Shouldn't wp-> be $wp->? Also, the $wp variable is undefined... I'm not a php expert... Jul 13, 2016 at 13:44

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