| Elektra 0.11.0

Plugin: reference

# Example: Alternative References

For this example the following configuration is used:

; this example uses the ni plugin syntax
; 1. metadata
[rootkey/ref]
check/reference = recursive
[otherkey/newref]
check/reference = alternative
; 2. configuration data
rootkey/ref = ../otherkey
otherkey/ref = ../yetanotherkey
otherkey/newref = ../otherotherkey
otherotherkey/ref = ../nonexistent
otherotherkey/newref = ../mergekey
yetanotherkey/ref = ../mergekey
yetanotherkey/newref = ../nonexistent
mergekey/ref = ../finalkey
mergekey/newref = ../finalkey
finalkey = ""

We mount it by executing:

cat << EOF > alternative.ini
; this example uses the ni plugin syntax
; 1. metadata
[rootkey/ref]
check/reference = recursive
[otherkey/newref]
check/reference = alternative
; 2. configuration data
rootkey/ref = ../otherkey
otherkey/ref = ../yetanotherkey
otherkey/newref = ../otherotherkey
otherotherkey/ref = ../nonexistent
otherotherkey/newref = ../mergekey
yetanotherkey/ref = ../mergekey
yetanotherkey/newref = ../nonexistent
mergekey/ref = ../finalkey
mergekey/newref = ../finalkey
finalkey = ""
EOF
kdb mount alternative.ini user:/tests/reference/alternative ni reference

The file contains a specification, which marks `user:/tests/reference/alternative/rootkey/ref` as our root reference key and `user:/tests/reference/alternative/otherkey/newref` as an alternative reference.

The actual configuration contains then a structure which is processed by the plugin like follows:

1. `user:/tests/reference/alternative/rootkey/ref` is read and its reference validated.
2. `user:/tests/reference/alternative/otherkey/ref` is read and its reference validated.
3. `user:/tests/reference/alternative/otherkey/newref` is discovered as an alternative reference and stored for later.
4. `user:/tests/reference/alternative/yetanotherkey/ref` is read and its reference validated.
5. `user:/tests/reference/alternative/mergekey/ref` is read and its reference validated.
6. `user:/tests/reference/alternative/finalkey` does not contain a reference, so we stop here.
7. Processing of the alternative reference chain from `user:/tests/reference/alternative/otherkey/newref` starts.
8. `user:/tests/reference/alternative/otherkey/newref` is read and its reference validated.
9. `user:/tests/reference/alternative/otherotherkey/newref` is read and its reference validated.
10. `user:/tests/reference/alternative/mergekey/newref` is read and its reference validated.
11. `user:/tests/reference/alternative/finalkey` does not contain a reference, so we stop here.

The resulting reference graph looks like this:

As you can see, the plugin completely ignores `user:/tests/reference/alternative/yetanotherkey/newref` as well as `user:/tests/reference/alternative/otherother/ref` and in turn does not throw an error because `user:/tests/reference/alternative/nonexistent` does not exist. However, the plugin does still exhaustively check both of the alternative reference chains. If you want to prohibit this, you can set the metakey `check/reference/restrict` to an empty value on whichever key you want to be a leaf node in the graph.

After we are done we can unmount the example with:

kdb umount user:/tests/reference/alternative