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debuggingdrupal-7

Drupal, entity_metadata_wrappers and debugging

For handling entities in Drupal I'm using Entity Metadata Wrappers (the "Drupal way").

It's really easy to start coding and see all the advantages it has... except when you get a fatal error and you are not clear where it comes from.

This is what the database log shows:

EntityMetadataWrapperException: Unknown data property field_whatever. at EntityStructureWrapper->getPropertyInfo() (line 335 of /var/www/html/sites/all/modules/entity/includes/entity.wrapper.inc).

Sadly, many times that "field_whatever" is "nid", "uid" or some very common property, so it's name is spread all over my code, which makes me difficult to get to the origin of the error.

I'm currently doing this:

  • Write a tiny piece of code and then run to see if something fails.
  • Using getPropertyInfo when handling entities with "not so common" fields.
  • Loosing hair.

What is worst is that sometimes the error does not appear when you are coding, but a week later. So it could be anywhere...

Is there any way of handling entity metadata wrapper errors better? Can I get better information in the database log and not just a line? A backtrace maybe?

Thanks.

Solution

  • Well, having the devel module active (just to see the nice krumo message) we can do something like this inside our module:

    <?php 

set_exception_handler('exception_with_trace');

function exception_with_trace($e)
{
    dpm($e->getTrace());
}

    That will return the backtrace error of the exception thrown by the entity metadata handler on the next page load (some page in your site where everything is running fine).

    Also you can set the exception handler exclusively and more elegant just for some pages or some users with some role... or when some parameter in the url is met, or when in some state of your Drupal site is met (ex. when a bool persistent variable 'exception_with_trace' is true). Even, under certain conditions and control, you can use it in production too.

    If the site does not work "at all" you can include it in your settings.php file, but instead of printing the trace, you must write the trace to a file and watch the trace in a different context (not Drupal but some php file).

    If exceptions are too long and are causing memory problems then getting the trace as string is also possible. See http://php.net/manual/es/exception.gettraceasstring.php

    Hope that helps.