What is the best way to remove a Drupal 7 field from a content type defined via the GUI? I want to use hook_update_N so the changes can be propagated to multiple servers upon running update.php. However I cannot seem to find a solution. db_drop_table() would make sense to me for custom defined schemas, but not for a content type/field defined through the GUI.
asked Jul 8, 2011 at 4:12
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you created a custom module to define a content type?– iStrykerCommented Jul 8, 2011 at 4:22
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iStryker: created the content type via the admin interface, added some fields, then exported via Feature. But now I want to remove one of those fields programatically.– amateur baristaCommented Jul 8, 2011 at 4:58
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Noted that D5 provides a content_field_instance_delete() function, documented here and here, but that function is not available for D7. Also it is curious what field.install in D7 core uses to delete a fields: _update_7000_field_delete_instance() - a custom "internal" function that is not available for others to use. For something so important as fields, it seems to me that there should be a "public" function available somewhere, and that's what I'm searching for.– amateur baristaCommented Jul 8, 2011 at 5:02
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Currently my "candidate" public function is field_delete_instance().– amateur baristaCommented Jul 8, 2011 at 5:05
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2 Answers
There are two api functions to delete fields:
field_delete_fieldTo delete the entire field (all instances of of the field)field_delete_instanceTo delete only an instance of a field - which is how it's attached to an entity.
If you don't want to reuse the field, it might be a bit cleaner to delete the entire field instead of only delete the instance of it on the content type in question. Only you can be the judge of that.
answered Jul 8, 2011 at 8:25
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2Worked like a charm. The function does not return any arguments, so when using in combination with a hook_update_N() I would recommend doing a watchdog() to log your update changes. Commented Jul 8, 2011 at 19:17
Yes, field_delete_instance() is the function to delete field instances.
Note that field_delete_instance() automatically calls field_delete_field() if there are no remaining instances, so field_delete_instance() is most likely all you'll ever need.
_update_7000_field_delete_instance() is designed for core update functions.
Example: in update function x_update_7000(), you are using field_delete_instance(). Then in x_update_7001(), you change the {field_config} table in an inconsistent way and field_delete_instance() obviously needs to be changed as well.
But now x_update_7000()'s call to field_delete_instance() would result in an error because the table is still in the old structure. However, the situation for contributed modules is different, since they should always be executed after all core updates and therefore need to work with the most recent core version.
But, this is a pattern that you might want to use for your own API functions which you are using in update functions.
Additionally, these _update functions do not execute hooks because the outcome is not predictable (for example because the module for which the update is run might be disabled).
