How to use PHP variables in a Graphql query?

Question

This is using WPGraphql with WordPress but I believe it's a general PHP and/or Graphql issue. I've been searching for 2 days now, and everything I've found is specific to some library or framework or otherwise not helpful. Any help with this is super appreciated.

The code below creates a variable $post_slug which contains the slug of the current post.

If I replace id: $post_slug with an actual post slug (id: "my-groovy-post") it works, but apparently $post_slug is undefined within the query.

<?php

$post_slug = get_post_field( 'post_name', get_post() );

$graphql = graphql([
    'query' => ' {
  post(idType: SLUG, id: $post_slug) {
    title
    content
    date
  }
}'
]);


echo '<pre>';
var_dump($graphql);
echo '</pre>';
?>

The results of my query

array(2) {
  ["errors"]=>
  array(1) {
    [0]=>
    array(3) {
      ["message"]=>
      string(37) "Variable "$post_slug" is not defined."
      ["extensions"]=>
      array(1) {
        ["category"]=>
        string(7) "graphql"
      }
      ["locations"]=>
      array(2) {
        [0]=>
        array(2) {
          ["line"]=>
          int(2)
          ["column"]=>
          int(27)
        }
        [1]=>
        array(2) {
          ["line"]=>
          int(1)
          ["column"]=>
          int(2)
        }
      }
    }
  }
  ["extensions"]=>
  array(1) {
    ["debug"]=>
    array(1) {
      [0]=>
      array(2) {
        ["type"]=>
        string(19) "DEBUG_LOGS_INACTIVE"
        ["message"]=>
        string(86) "GraphQL Debug logging is not active. To see debug logs, GRAPHQL_DEBUG must be enabled."
      }
    }
  }
}

Double-quote your string if you expect $post_slug to be interpolated within it. — ADyson
– ADyson, Commented May 10, 2022 at 23:24
Thanks ADyson but no luck. Double quotes removes the part about $post_slug being undefined but then returns a null result. — Ted
– Ted, Commented May 10, 2022 at 23:52
Well my bit works in the sense of interpolating the variable properly. The problem you seem to have now is that graphQL expected a numeric value, but your $post_slug value contains p instead. So I don't really know graphQL but I can use google, and it seems it wants you to quote the field so it can be treated as a string in the context of the graphQL query. So you can add escaped quote marks, like this: 3v4l.org/XY9SG . Or you go back to single-quoted PHP string, add the quote marks verbatim and concatenate the slug value, like this: 3v4l.org/suI5r . Same result either way — ADyson
– ADyson, Commented May 11, 2022 at 10:05

Ted · Accepted Answer · 2022-05-11 21:11:34Z

1

Thank you to @ADyson for his persistence in figuring this out. The solution was twofold -- first wrap the query in double quotes for interpolation, then wrap the variable in escaped double quotes. Here's the updated code...

<?php
$post_slug = get_post_field( 'post_name', get_post() );

$graphql = graphql([
    'query' => "{
  post(idType: SLUG, id: \"$post_slug\") {
    title
    content
    date
  }
}"
]);

echo '<pre>';
var_dump($graphql);
echo '</pre>';
?>

edited May 11, 2022 at 21:11

answered May 11, 2022 at 18:24

Ted

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