How to only show posts with a certain custom field filled out

The request

How do I only show posts with a certain ACF or custom field filled out? View original thread

The solution

<Loop type=post_type_name custom_field=field_name>
  <Field title />
</Loop>

The explanation

While this can be done with conditional logic, the best way to do this is by adding a custom_field query parameter that filters the query to only display items for which a specific field exists. Since we're simply wanting to show posts for which a certain custom field exists, there's no need to add any other parameters.

That being said, if we wanted to instead display posts in which a certain field matched a specific value, we could use custom_field_value="some value". We could use the parameter custom_field_compare to choose how we're comparing the custom field to the value we're specifying, such as custom_field_compare=not if we wanted to only show posts that had a custom field that didn't match the value specified in the custom_field_value parameter.