Q&V: Auto-generate the lookup key_field

[urapadmin]

Currently I have to define a lookup and state the key field:

    to_locus:
      element_type:
        text: "#(unit/term_for_locus)"
        name: "TextField"
        value: "#(locus_relations/uid_locus_2_related)"
        lookup:
          lookup_type: "record"
          record_type: "locus"
          display_value: "arch_context"
          key_field: "uid"

That's redundant because there is also the loopup relation in the DSD:
uid_locus_2_related: [datatype(UUID), "lookup('locus', 'uid')"]

I thought to get the key field into the lookup data from the DSD lookup statement on the client side. But first this would be insane and slow to always lookup and interpret the DSD and second I don't even know when resolving the lookup on the client side which lookup statement in the dsd was responsible. At least not on the client's side. Instead of stating the key_field manually in the PLD, I want to try to make the server auto-generate the key_field entry (if it isn't set manually) when it is creating the record for the lookup data.

[urapadmin]

There is a complication here that is presumably of mere theoretical nature: It is possible that a table is looked up with different key fields. One table could look up a site by ''lookup(site, id)" and another table could use "lookup(site, uid)" or so. In that case it is not possible in the current structure to come up with the right key for the ui_element.
But since I find this rather theoretical I can live with having the manual way of setting a key as a solution for such an exotic case. In almost all cases it will be the same field in the lookup table that's being used a key.

[urapadmin]

Implemented as planned. The code will issue a warning in Kiosk if either the key_field could not be determined because there are different lookups using different keys or the key_field could not be determined at all but is not stated manually.