drupal--why $node->taxonomy is an array

someone wrote this code.

 foreach ($node->taxonomy as $term) {
 开发者_如何学JAVA$tids[] = 't.tid = %d';
  $args[] = $term->tid;
 }

how he knows that in foreach "$node->taxonomy" is an array? and when i loop it, foreach ($node->taxonomy as $term) { } the output that i get will be the $term's value. i don't know how it is change into the 't.tid = %d' and $term->tid. thank you.

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In Drupal-related code, a $node is almost always an object produced by the node_load() function. Since every module has the opportunity to add its own properties to this object, it's very hard to find a central documentation of these properties.

By experience and by variable inspection, seasoned Drupal developers know that when set $node->taxonomy is always an array of term object (as returned by the taxonomy_get_term() function) indexed by their respective ids (named tids, for Term ID). This array is set by the taxonomy_nodeapi() function when $op == 'load' and is produced by the taxonomy_get_terms() function.

The question give little information but we can guess that the loop is meant to build two arrays used to generate a database query that filter on the tid column matching those of the $node object. Because the terms' data is already stored in the items of $node->taxonomy, let's hope that this query is not used to re-load the terms to display some of their name and/or description. Collecting 't.tid = %d' is probably a bad idea, the query would be better build with a single "tid in (". db_placeholder($args) .")" WHERE clause after collecting all the tids in $args.

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The question is very unclear. All Items under the node object are arrays. You can check it yourself bu using:

print_r($node);
die;

Or using any PHP debugger.

for the foreach, It is very simple foreach... I don't understand what is the problem with that.

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t.tid is simply an SQL query. %d is a placeholder for $args[], which consists of $term->tid. It's like this structure: PDO connections.