Ah, I didn’t find that configuration page. The Display Modes diaglog, could do with a reference to it. As it really influences how the checkboxes work. The single option on the Display Modes dialog to change the default to unchecked, tricked me into thinking that this was the only option.
The settings, as you suggested, with ‘All the selected terms must match, exclude unselected’ did not work. See the discussion below for screenshots 4, 5 and 6. The behaviour I am after is when ‘At least one selected terms should match’.
Currently, I am using ‘Multiselect with search’, checking a child term, the taxonomy returns only those records with the child term assigned. If the parent is selected, the hierarchy includes all records under that term, whether they have the parent assigned or any of the child-terms. Records do not need to be tagged with the parent term, only the child term. WordPress returning the superset, of all child terms and any with the parent term. In my taxonomy, using multiselect or dropdown, and selecting the parent term ‘High Wycombe (outer)’ search returns 10,057 hits. As expected, being a superset of the parent and all the children. The parent term ‘High Wycombe (outer)’ is only tagged explicitly by 375 records. The superset of this and all the children is 10,057.
The Checkbox display mode option does not quite work in the same way. To get the superset of 10.0157, am using the checkbox option ‘At least one selected terms should match’ The result is in screenshot SearchResults1 below. Selecting the checkbox ‘High Wycombe (outer), sub-terms are opened unchecked and 10,057 results are returned. All good.
The way the Checkbox selection is implemented, if one of the child options is selected, the result stays as 10,057, because at this stage both parent and child are selected and WordPress returns the superset. As in SearchResults2. But if I uncheck the parent ‘High Wycombe (outer)’, I get the right number of hits for the child, 255, as only the child-term ‘Abbey Grounds’ is selected. But the hierarchy closes up and there is no indication of which child term was selected. As in SearchResults3. The selected child term could be anywhere in the nested hierarchy. If the user wants to uncheck it, they have to remember where it was and which parent it was under.
A solution to the loss of visibility of the selected child terms, is to leave the subcatergory open if a child is selected and the parent unselected. My preferable solution, would be not to check the parent when it is first clicked, but to just open the child-terms under it. Another issue is that in the selection UI, there is no differentiation between a term that does have children and a term that does not have children. In other solutions, parents with children have a + icon to similar to open the sub-terms without checking the parent. The icon indicating that they can drill down further. The current checkbox support does not allow this.
If I use the checkbox mode ‘All the selected terms must match, exclude unselected’ the results are completely unexpected. Selecting ‘High Wycombe (outer)’ only returns those records which are explicitly tagged with HW (outer). As per SearchResults4, 1942 hits. I had expected the superset. Also its not clear where the 1942 hits are arrived at, the parent only assigned explictly to 375 records. To get the superset, it looks like I have to check the parent and all the children. Which seems to get to the expected 10,000+.
Selecting the first child, Abbey Ground, results in SearchResults5 of 2184. Summing the bad result of 1942 with the child. As per the behaviour shown in SearchResults4, this is not unexpected. But should still be the superset of 10,057.
Where it gets really weird, is unchecking the parent HW (outer), the sub-terms are closed (this is not the right behaviour, as per the above, it should stay open), but very weirdly, the result is 1699 as in SearchResults6. This looks to be the parent minus the child, 1942 – 255. Which is completely the wrong behaviour. Something is broken with ‘All the selected terms must match, exclude unselected’.
In my implementation I interpret the URL search terms and display the terms selected. These appear at the bottom on each screenshot. So its possible to see what terms ASP thinks are selected. These appear as expected. The results returned when using ‘All the selected terms must match, exclude unselected’ certainly do not match the terms when a parent is selected.