Github user ijokarumawak commented on the issue:
https://github.com/apache/nifi/pull/2777
Thanks @markap14 for pointing that. Separating the coordinate and context
make sense and implementations will be cleaner by doing so. Although I agree
with the idea, let me try to explain why I wanted to put everything into the
same map.
I wanted to muddle all variables into the same map because some lookup
target, such as URL for the RestLookupService have both lookup coordinate and
environment depending part that can be passed as FlowFile attributes or
variable registry.
For example, let's say we want to make following URL to be populated by a
Expression Language to be used by RestLookupService.
`http://test.example.com:8080/service/john.smith/friend/12345`
I think the URL has both lookup and contextual part in it.
- `john.smith and `12345` are lookup coordinates that vary from input, in
LookupRecord context, it varies per recocrd
- But hostname and port is more of contextual values, that varies per
FlowFile or environment
If the URL property is configured as
`http://${apiHost}:${apiPort}/service/${userName}/friend/${friendId}`, and if
it can only refer lookup coordinate, then `apiHost` and `apiPort` need to be
set for each record lookup. And to do so, user need to configure dynamic
properties at LookupRecord processor using record paths, which can be awkward
since RecordPathValidator doesn't allow literal String value. A work-around is
to use `concat('test.example.com')` to return the constant value for every
record lookup.
To make this scenario more flexible while meeting with the idea of
separating lookup coordinates and context, I wrote MikeThomsen/nifi#1 so that
target URL can be configured by 2 properties (if necessary). `BASE_URL` can use
Variable Registry, and `URL` can use coordinate.
If we pursue the path to separate lookup and coordinate more
implementations like that will be needed in different places. That has both
pros / cons I think.
On the other hand, the variables those can be referred by an EL is already
muddled a lot IMHO. It contains System properties, Variable registry, and
FlowFile attribute values and EL can utilize those without knowing where it's
configured.
Adding those values into lookup coordinate may not sound that wrong, if we
keep the consistent overlaying order.
---
