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I am studying how to write more secure WordPress code by implementing validation, sanitization and data escaping wherever necessary. Validation and escaping makes perfect sense, but I am a little confused about sanitization.

If I use a function like add_post_meta, does this function do sanitization for me? What about set_option or other ones that interact with the database. I usually interact with the database via these functions. In which situations do I need to worry about sanitization myself?

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    You're talking about SQL sanitising correct? – Tom J Nowell Jan 19 '17 at 12:11
  • Yes, preparing data to be stored inside the database. – Mauro Bringolf Jan 19 '17 at 12:16
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    This should answer your question - stackoverflow.com/questions/16122790/… – Ravi Shinde Jan 19 '17 at 12:23
  • Thank you! I'm going through several articles on this topics right now and most of them use code examples that validate and sanitize input before passing it to one of these functions. Does that mean that is unnecessary? – Mauro Bringolf Jan 19 '17 at 12:27
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Yes, WordPress will sanitise data on its way to the database, so long as you use the APIs.

If you're using the wpdb object however you'll need to use the prepare method to sanitise. I recommend against writing SQL queries as it bypasses object caches etc, but if you must write your own SQL, use wpdb to prepare and execute it

For calls such as WP_Query, get_posts, add_post_meta etc etc sanitisation occurs

Note that this is purely DB sanitisation, any additional sanitisation or validation you require, such as trimming trailing spaces, validation of URLs, stripping tags, escaping, etc, must all be done in your code

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    @MauroBringolf great :) if you could mark it as the correct answer? – Tom J Nowell Jan 19 '17 at 16:00

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