Title: add_filter problem
Last modified: August 18, 2016

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# add_filter problem

 *  Resolved [till](https://wordpress.org/support/users/till/)
 * (@till)
 * [19 years, 6 months ago](https://wordpress.org/support/topic/add_filter-problem/)
 * I wrote a plugin which is supposed to filter my post_content and add if applicable
   a footer to it. What I am doing is, inside the filter I grab `$GLOBALS['wp_query']-
   >post->ID` and perform a couple database queries to check if the footer applies
   to this post.
 * It’s nothing special really.
 * To apply the filter I did this underneath:
    `add_filter('the_content', 'my_filter',
   2);` `add_filter('the_excerpt', 'my_filter', 2);`
 * The problem is – on static content pages (where the filter does not apply anyway),
   all works well. However, when I am on my blog’s frontpage or on an entry page,
   it does not display any categories, blogroll and archives.
 * I have no idea why.

Viewing 4 replies - 1 through 4 (of 4 total)

 *  [Kafkaesqui](https://wordpress.org/support/users/kafkaesqui/)
 * (@kafkaesqui)
 * [19 years, 6 months ago](https://wordpress.org/support/topic/add_filter-problem/#post-479783)
 * Try checking the source of those pages through your browser and see if any error
   shows up at the location where sidebar appears to end.
 * Beyond that, we’d need a lot clearer idea of what your plugin actually does to
   work out what’s going on here.
 *  Thread Starter [till](https://wordpress.org/support/users/till/)
 * (@till)
 * [19 years, 6 months ago](https://wordpress.org/support/topic/add_filter-problem/#post-479821)
 * Ok, first of, thanks for your reply. 🙂
 * I’ll try to be more clear.
 * This is my filter:
    `function my_filter($string_text) { $post_id = $GLOBALS['
   wp_query']->post->ID; if (empty($post_id)) { return $string_text; } /* query 
   database and check if extra information applies to this post. */ $query = "...";...
   if (mysql_num_rows($res) == 0) { return $string_text; } $infoObj = mysql_fetch_object(
   $res); $string_text.= sprintf( '<ul><li>%s</li></ul>', $infoObj->foo ); return
   $string_text; }
 * So this is what I do.
 * Checking the source, I see no HTML or PHP errors. For example, once I activate
   the filter, the categories are gone missing. But there is no error, it just says“
   >> No categories” in place where the list should be.
 * Any idea?
 *  Thread Starter [till](https://wordpress.org/support/users/till/)
 * (@till)
 * [19 years, 5 months ago](https://wordpress.org/support/topic/add_filter-problem/#post-479997)
 * I checked the source code of the website again. There’s no error in the HTML.
   Any other idea? 😐
 * This is the only filter doing this. The thing is also, I embeded a function to
   email me from inside the filter, to check the contents on the frontpage which
   are parsed. Nothing from the sidebar actually gets in there.
 * Still, once I enable it on the frontpage as well, categories and static pages
   disappear. Like I’m overwriting some internal array? 😐
 *  Thread Starter [till](https://wordpress.org/support/users/till/)
 * (@till)
 * [19 years, 5 months ago](https://wordpress.org/support/topic/add_filter-problem/#post-479999)
 * Ok, I found the error.
 * Inside my plugin, I opened a connection. And when I closed it, it screwed up 
   the rest of the site. So leaving it open fixed the situation for me. Not sure
   why though.

Viewing 4 replies - 1 through 4 (of 4 total)

The topic ‘add_filter problem’ is closed to new replies.

## Tags

 * [content](https://wordpress.org/support/topic-tag/content/)
 * [filter](https://wordpress.org/support/topic-tag/filter/)
 * [output](https://wordpress.org/support/topic-tag/output/)
 * [the_content](https://wordpress.org/support/topic-tag/the_content/)
 * [the_excerpt](https://wordpress.org/support/topic-tag/the_excerpt/)

 * 4 replies
 * 2 participants
 * Last reply from: [till](https://wordpress.org/support/users/till/)
 * Last activity: [19 years, 5 months ago](https://wordpress.org/support/topic/add_filter-problem/#post-479999)
 * Status: resolved

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