Disable _all_ filter option

[JeffersonBledsoe]

This PR adds an option to the collection filter settings panel to disable the 'All' option from the filter list. In order to provide a default filtering fallback, this PR also adds a redirect to the current page with collectionfilter=1 added as a query string if the collectionfilter is about to be displayed but the query string is missing. This is because the filtering of the collection is done by an event handler for each page traversal on the site. When the all option is disabled, we will use the first option from the filter as the default filter.

Closes #137

[JeffersonBledsoe]

@petschki Any chance you could have a look over this?

[petschki]

Sorry for the late response. While it makes sense to disable the all option for filteritems, there must be a better way to inject the first filteritem as default filtering than redirecting again to the same page with collectionfilter=1 in query. This is a major performance downgrade of the whole package and I'm against merging it into master. @thet @agitator any thoughts?

[djay]

@petschki it shouldn't be a performance impact most of the time. The whole reason to do the redirect is avoid performance problems.
The only time the redirect happens is if the filter with "all" disabled appears the first time without collectionfilter=1. After that there is no cost. If the All is not disabled there is no cost. On other parts of the site there is no cost.

If you can think of another way to achieve this without the redirect then great but we did think about it and couldn't come up with another way. The nature of collectionfilter is that portlets can't influence the query until it's hit the collection for first time. Not without monkey patching collections and centrally storing the filter definitions outside of the portlets and onto the collection itself.

[djay]

@petschki any update on this?

[JeffersonBledsoe]

Hi @petschki, any chance you've had any more thoughts on how it would be possible to inject collectionfilter=1 into the query without redirecting? As @djay mentioned, there should not be any performance impact most of the time, but you're right in that it would be great to avoid this completely. I'm working on a few changes to this PR and would be great if there were a way to get this merged eventually!

[JeffersonBledsoe]

@petschki Had to pin the version of black to the one before the stable release as they dropped Python2.7 support (e.g. formatting tries to remove all the u characters). Happy for this to be in this PR, or want it in a separate one?

[petschki]

Hi, I've quickly tried this feature in a project of ours and found out the following:

• if there's only one filteritem on a page with default_filter_behavior="Select first" it works (only tested the portlet)
• if there is a second filteritem (no default filter behavior set), I get redirected to the page with ?collectionfilter=1 only ... the first filteritem has the first value selected, but the listing is not constrained to the first value.

Does this work with multiple group_by filteritems or did I do something wrong?