documentation on arguements?

Question

I have seen many different parameters or arguments that can be passed to a query. For example, category_in, category_and term_id to name a few. Some of these can be found by using print_r to print out the object. ( If I have that right ). Others like the category__in I have been unable to find in codex. Is there a trick to learning about these parameters? How do I find them?

Answer 1

They're all in the codex page for WP_Query.

Answer 2

As a compliment to Milo's answer and WP_Query Codex entry above, here is a nice little cheat-sheet and reference which summarizes the $arguments used with WP_Query;

WordPress Query Comprehensive Reference
https://gist.github.com/2023628
^{Compiled by luetkemj - luetkemj.com}

...and here's a little gist to go along with it for debugging your query,

Debugging WP_Query
https://gist.github.com/3699573
^{from wpsmith}

add_action( 'template_redirect', 'wps_debug' );
function wps_debug() {
    global $wp_query;
    if( isset( $_GET['debug'] ) ) {
        echo '<pre>'; print_r( $wp_query ); echo '</pre>';
    }
}

PS. this is just a quick and dirty way to see whats going on. There are other tools, snippets and plugins that do this in a more organized fashion. But that's a discussion for another time.

Answer 3

All of those are in the Codex.

http://codex.wordpress.org/Class_Reference/WP_Query

I feel guilty about posting this as an answer but it does very directly answer your questions, "Is there a trick to learning about these parameters?" and "How do I find them?"

The trick is to search the Codex, and to read the Codex. Follow the links in the Codex. Look in the source code, a link to which is provided in many, but not all, of the Codex entries.

Yes, print_r() helps a lot. var_dump() is better in that it will output information even for empty strings, NULLs, booleans, etc. Its output is harder to read, but you get used to it.

Answer 4

The code itself is also a great place to learn about all possible arguments. One advantage over all the other methods (including the Codexs) is that it never gets outdated. Here's the code for WP_Query: http://core.trac.wordpress.org/browser/trunk/wp-includes/query.php

The arguments you are referring to are in its parse_tax_query method.