bionic (7) elektra-cascading.7.gz

NAME

       elektra-cascading - of key names

       Cascading  is  the  triggering  of  secondary  actions.  For  configuration  it means that first the user
       configuration is read and if this attempt fails, the system configuration is used as fallback.

       The idea is that the application installs a configuration storage with default settings that can only  be
       changed  by  the  administrator.  But  every  user  has  the possibility to override parts of this system
       configuration regarding the  user´s  needs  in  the  *user  configuration.  To  sum  up,  besides  system
       configuration,  users  have  their  own  key  databases that can override the settings according to their
       preferences.

       Thus when a key starts with / such cascading will automatically performed.

SPEC

       Keys in spec allow us to specify which keys are read by the application, which fallback it might have and
       which  is  the  default value using meta data. The implementation of these features happened in ksLookup.
       When cascading keys (those starting with /) are used following features are available (in the  meta  data
       of respective spec-keys):

       •   override/#: use these keys in favour of the key itself (note that # is the syntax for arrays, e.g. #0
           for the first element, #_10 for the 11th and so on)

       •   namespace/#: instead of using  all  namespaces  in  the  predefined  order,  one  can  specify  which
           namespaces should be searched in which order

       •   fallback/#:  when  no  key  was  found in any of the (specified) namespaces the fallback-keys will be
           searched

       •   default: this value will be used if nothing else was found

CASCADING

       When cascading keys (those starting with /) the lookup will work in the following way (it can be debugged
       with kdb get -v):

       1.) In the spec-key the override/# keys will be considered. 2.) If, in the spec-key, a namespace/# exist,
       those  namespaces  will  be  used.  3.)  Otherwise,  all  namespaces  will  be  considered,   see   here.
       /doc/help/elektra-namespaces.md  4.)  In  the spec-key the fallback/# keys will be considered. 5.) In the
       spec-key the default value will be returned.

       See application integration /doc/tutorials/application-integration.md for how to use cascading  names  in
       the context of applications.

       Read more about namespaces. /doc/help/elektra-namespaces.md

                                                    July 2017                               ELEKTRA-CASCADING(7)