Limiting a taxonomy to only having 1 term checked

One thing I dislike about WordPress taxonomies is that there is no built in way to limit a post to only having 1 term for a certain taxonomy. You always have to have a metabox with all the terms shown alongside checkboxes, and it allows you to check as many as you want.

Sometimes you might want to limit 1 term from a taxonomy. A really quick way to do that is with the following piece of code you can put in your functions file:

add_action( 'admin_footer', 'nk_limit_taxonomy', 10, 1 );
	function nk_limit_taxonomy( $array ) {&nbsp;
		?>
		<script>
		   jQuery("input[name=\"tax_input[product_category][]\"]").click(function () {
		       selected = jQuery("input[name=\"tax_input[product_category][]\"]").filter(":checked").length;
		       if (selected > 1){
		           jQuery("input[name=\"tax_input[product_category][]\"]").each(function () {
		                jQuery(this).attr("checked", false);
		           });
		           jQuery(this).attr("checked", true);
		       }
		   });&nbsp;
		</script>
		<?php
	}

add_action( 'admin_footer', 'nk_limit_taxonomy', 10, 1 );

function nk_limit_taxonomy( $array ) { 

jQuery("input[name=\"tax_input[product_category][]\"]").click(function () {

selected = jQuery("input[name=\"tax_input[product_category][]\"]").filter(":checked").length;

if (selected > 1){

jQuery("input[name=\"tax_input[product_category][]\"]").each(function () {

jQuery(this).attr("checked", false);

});

jQuery(this).attr("checked", true);

}

}); 

</script>

<?php

}

This effectively prevents the user from selecting more than 1 term on a post. It will unselect everything if you attempt to check another. It’s not foolproof, but for the casual user it should be adequate in what you need.