When should you use WP_Query vs query_posts() vs get_posts()?

Question

It seems like half the tutorials in the codex and around the blogosphere use query_posts() and half use WP_Query. What's the deal?

Answer 1

• query_posts() should be used in one and only case if you need to modify main query of page. It sets a lot of global variables and will lead to obscure and horrible bugs if used in any other place and for any other purpose;
• get_posts() is very similar in mechanics and accepts same arguments, but returns array of posts, doesn't modify global variables and is safe to use anywhere;
• WP_Query class power both behind the scenes, but you can also create and work with own object of it. Bit more complex, less restrictions, also safe to use anywhere.

I want to stress that query_posts() wrongfully overused in many tutorials around. It is one of the most widespread bad practices.

Answer 2

The basic difference is that query_posts() is really only for modifying the current Loop. Once you're done it's necessary to reset the loop and send it on its merry way. This method is also a little easier to understand, simply because your "query" is basically a URL string that you pass to the function, like so:

query_posts('meta_key=color&meta_value=blue'); 

On the other hand, wp_query is more of a general purpose tool, and is more like directly writing MySQL queries than query_posts() is. You can also use it anywhere (not just in the Loop) and it doesn't interfere with any currently running post queries.

I tend to use wp_query more often, as it happens. Really, it's going to come down to your specific case.

Answer 3

If I recall reading right, essentially "the loop" is doing WP_Queries in the core files, but in an easier to understand way.