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   Contributed by memuller — 3 years ago

   Return values when no meta field is found
   If a meta field with the given $key isn’t found for the given $post_id, the return value varies:

   If $single is true, an empty string is returned.
   If $single is false, an empty array is returned.

   Since both evaluate as false, you can use get_post_meta directly in conditionals, like this:

   if( ! get_post_meta( '1', 'non-existing_meta', true ) ) {}
   if( ! get_post_meta( '1', 'non-existing_meta', false ) ) {}
   // both ifs will get run if no meta field is found; since
   // array() == false and '' == false
   

   What if I want to store an empty string?
   If for some reason your with to store an empty string or array into your meta field, get_post_meta will not be reliable when checking if the given meta field exists.
   In this case, you can use get_post_custom_keys to do so:

   if( ! in_array( 'given_key', get_post_custom_keys( '1' ) ) ) {} 
   // this correctly checks for the existence of the given key, 
   // even if it's empty or has a value that evaluates as false. 
   
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   Contributed by Codex — 3 years ago

   Show the first value of the specified key inside a loop

   $key_1_value = get_post_meta( get_the_ID(), 'key_1', true );
   // Check if the custom field has a value.
   if ( ! empty( $key_1_value ) ) {
   	echo $key_1_value;
   }
   
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   Contributed by Codex — 3 years ago

   Default Usage
   Get the meta for all keys for the current post:

   <?php $meta = get_post_meta( get_the_ID() ); ?>
   

   Get all meta for a single key for the current post:

   <?php $key_1_values = get_post_meta( get_the_ID(), 'key_1' ); ?>
   

   Get the first value of a meta key for the current post:

   <?php $key_1_value = get_post_meta( get_the_ID(), 'key_1', true ); ?>
   
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   Contributed by Ian Dunn — 2 years ago

   The best thing about this function is that you no longer need to use it :)

   Since r21559 (v3.5), you can just call $post->foo to fetch the equivalent of get_post_meta( $post->ID, 'foo', true ).

   You can even extend that to introduce dynamically-generated fields, so you can call echo esc_html( $post->bar ) instead of $bar = some_custom_logic( get_post_meta( $post->ID, 'bar', true ) ); echo esc_html( $bar ).

   This makes code a lot cleaner and more readable.

   add_filter( 'get_post_metadata', 'add_dynamic_post_meta', 10, 4 );
   
   /**
    * Add dynamically-generated "post meta" to `\WP_Post` objects
    *
    * This makes it possible to access dynamic data related to a post object by simply referencing `$post->foo`.
    * That keeps the calling code much cleaner than if it were to have to do something like
    * `$foo = some_custom_logic( get_post_meta( $post->ID, 'bar', true ) ); echo esc_html( $foo )`.
    *
    * @param mixed  $value
    * @param int    $post_id
    * @param string $meta_key
    * @param int    $single   @todo handle the case where this is false
    *
    * @return mixed
    *      `null` to instruct `get_metadata()` to pull the value from the database
    *      Any non-null value will be returned as if it were pulled from the database
    */
   function add_dynamic_post_meta( $value, $post_id, $meta_key, $single ) {
   	$post = get_post( $post_id );
   
   	if ( 'page' != $post->post_type ) {
   		return $value;
   	}
   
   	switch ( $meta_key ) {
   		case 'verbose_page_template':
   			$value = "The page template is " . ( $post->_wp_page_template ?: 'not assigned' );
   			break;
   	}
   
   	return $value;
   }
   

   Expand full source codeCollapse full source code
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   Contributed by Codex — 3 years ago

   Retrieve a Custom Field Thumbnail Url
   While you are in the WordPress Loop, you can use this code to retrieve a custom field. In this example, the thumbnail image url is in a custom field named “thumb”.

   <?php if ( get_post_meta( get_the_ID(), 'thumb', true ) ) : ?>
   	<a href="<?php the_permalink() ?>" rel="bookmark">
   		<img class="thumb" src="<?php echo esc_url( get_post_meta( get_the_ID(), 'thumb', true ) ); ?>" alt="<?php the_title_attribute(); ?>" />
   	</a>
   <?php endif; ?>
   
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   Contributed by BjornW — 3 years ago

   If you want to hide postmeta keys from the customfields prefix the key name with an underscore.
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   Contributed by BjornW — 3 years ago

   Post meta keys are case-sensitive
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   Contributed by stijnjanmaat — 2 years ago

   When you don’t specify a $key (”) and set $single to true in get_post_meta, it will return all keys still with an array of values.

   $meta = get_post_meta(get_the_ID(), '', true);
   print_r($meta);
   //Array ( [key_1] => Array ( [0] => value_1 ), [key_2] => Array ( [0] => value_2 ) )
   
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   Contributed by kommasri — 2 years ago

   Display single meta value using meta key

   <?php 
   $meta_print_value=get_post_meta(get_the_ID(),'conference_speaker_business',true);
   echo($meta_print_value);
   ?>
   
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    Contributed by Nadav Rotchild — 2 years ago

    If the value of the $key parameter is falsy get_post_meta will return the entire post meta array, even if $single is set to true. for example:

    get_post_meta( $post_id, FALSE, TRUE); //Returns all the post meta fields as an array.
    get_post_meta( $post_id, '0', TRUE); //Will also return all the post meta fields as an array. 
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    Contributed by Mario Valney — 12 months ago

    False if post ID isn’t absint or is 0

    Passing $post_id == 0 (or anything not a absint) will return false no matter $single.

    $meta = get_post_meta( 0, 'key', true );
    var_dump( $meta ); // bool(false)
    
    $meta = get_post_meta( 0, 'key', false );
    var_dump( $meta ); // bool(false)
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    Contributed by sltmunky69 — 2 years ago

    When I had tons of meta keys to work with to display some custom content for custom post types, instead of making several dozen calls to the get_post_meta function to grab the keys I wanted, I wrote this function instead. Basically it gets all of the meta keys and filters out all of the arrays with single values while maintaining any arrays that actually do have multiple values and returns an associative array of the results. If you have lots of single values to get, it saves you from having to iterate over every result to get your $k=>$v pairs so you can just access them by $mk[‘my_custom_meta_key’].
    function array_push_assoc($array, $key, $value){
$array[$key] = $value;
return $array;
}

    function filter_gpm($array){
$mk = array();
foreach($array as $k => $v){
if(is_array($v) && count($v) == 1){
$mk = array_push_assoc($mk, $k, $v[0]);
} else {
$mk = array_push_assoc($mk, $k, $v);
}
}
return $mk;
}
    Call it like so
    $mk = filter_gpm( get_post_meta( get_the_ID() ) );

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