Lenses (selecting a subset of fields from a node)

Just bumping my own post and mentioning that the module is almost ready to release. It turned out to be a much bigger project than I anticipated, but I think I've managed to create a configurable and (hopefully) useful solution to the general problem of how to present the same piece of content more than one way on a website... allowing you complete freedom to show or hide "fields" (by which I mean core Drupal fields such as title/body, in addition to CCK fields and Taxonomy vocabularies) in different settings, as appropriate.

I'll post some code soon (and eventually put this on drupal.org, of course), but I still have to tidy up a few things. I'm still very interested in feedback and ideas, if anyone has any. (Integration with Views 2 is something I'll be very interested in for Drupal 6, probably by making lenses available as a row plugin.)

Since screenshots are better than words, here is a small example of the Lenses module in action:

You can see that the entire node (i.e., the entire lasagna recipe) is visible under a menu tab, but there are other menu tabs (a.k.a., the "lenses") that only show some of the fields, thereby allowing you to focus on parts of the recipe without having to see the whole thing. Note that the same thing can be done on the node edit/create form, by the way. The module also comes with a permissions system, so if you wanted to hide the entire recipe but allow users to see some individual parts of it, that's possible too. It's also worth pointing out that the same field can easily appear in multiple lenses; for example, "preparation time" (circled in red) is a field that show up under the recipe's directions, but also might be useful in a quick summary of the recipe, as below.

Thanks for your comments and suggestions!

First of all, I think my description of the permission system wasn't written so clearly the first time. I'm not planning to implement "per-field" permissions in this module, but rather "per-lens" permissions. In other words, I've set it up so you can deny access to a lens on a per-user-role basis (for example, you could hide the "Directions" menu tab in the above screenshot from some users), but they still may be able to access some of the fields in that lens in other contexts (e.g., the "Summary" menu tab will still let them see the "Preparation time" field).

I think it will be possible to use Lenses to completely hide some fields from certain roles (by cleverly controlling which lenses they have access to and which fields are in those lenses), but that's probably only a good idea if the fields are being hidden for aesthetic reasons. If the goal is security, then the right way to do it is still through a separate field permissions module (and thanks for pointing out that this might be in CCK itself in D6 -- I didn't realize that was a possibility). And the Lenses module will definitely "play nice" with field permissions modules, since internally, it never specifically grants access to any field -- it only denies access to all fields that aren't part of the lens.

Regarding field groups, that's a good question... as things currently stand, the module is aware of field grouping on a fundamental level, in the sense that when it goes out and collects information about fields, any field can declare itself as "group" that contains other fields. (As I've implemented it now, all CCK fieldgroups declare themselves as "groups", of course, but I've also defined a group for Taxonomy -- this controls the entire taxonomy fieldset as a whole, rather than on a vocabulary-by-vocabulary basis).

I'm still trying to decide the following, though: If you click a checkbox to specifically include a group in a lens (or to specifically exclude the group from the lens), what does that mean for the individual fields inside that group? Suggestions are welcome, but I think the simplest way to handle it might just be that including/excluding a group automatically includes/excludes all the fields it contains. (Putting a group in a lens is therefore sort of a brute force tool.)

As for the overall UI, the basic list you started making is similar to what I had in mind (actually, the form for adding a lens is the one big part of the module that isn't written yet, which is why I haven't bothered posting any code yet!). But in terms of functionality, some of the things that the module can already do internally (and therefore which will actually show up on the form once I finish writing it) include:

• Lens name
• What to append to the URL to access the lens (e.g., node/123/view/something)
• List of fields
• Where should the lens apply (viewing a node, editing a node, creating a node, or any of the above)?
• What content types should it apply to?
• Who should be able to access it? (can restrict by user role, or also make it a "private" lens that only the person who created it can use)
• Whether to make the lens override the default menu tab (e.g., to have it visible at node/123, node/123/edit, etc... as opposed to the default view which shows all fields and that is normally visible at that URL)
• etc.

Any other possible options people can think of?

This notion that there are different field subsets for a node is built into Drupal6 and into CCK for 6. Search the code for $node->build_mode or see the tabs and subtabs on the Display page of a content type (requires CCK). It would be handy for a module (why not lens?) to let the user make own $build->mode. Then the admin would use the Display tab to customize it.