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The best way to understand what a hook does is to look at where it occurs in the source code.
do_action( "hook_name" )apply_filters( "hook_name", "what_to_filter" ).Remember, this hook may occur in more than one file. Moreover, the hook's context may change from version to version.
| Line | Code |
|---|---|
| 40 | |
| 41 | global $wpdb; |
| 42 | |
| 43 | $column = esc_sql($meta_type . '_id'); |
| 44 | |
| 45 | // expected_slashed ($meta_key) |
| 46 | $meta_key = stripslashes($meta_key); |
| 47 | $meta_value = stripslashes_deep($meta_value); |
| 48 | |
| 49 | $check = apply_filters( "add_{$meta_type}_metadata", null, $object_id, $meta_key, $meta_value, $unique ); |
| 50 | if ( null !== $check ) |
| 51 | return (bool) $check; |
| 52 | |
| 53 | if ( $unique && $wpdb->get_var( $wpdb->prepare( |
| 54 | "SELECT COUNT(*) FROM $table WHERE meta_key = %s AND $column = %d", |
| 55 | $meta_key, $object_id ) ) ) |
| 56 | return false; |
| 57 | |
| 58 | $_meta_value = $meta_value; |