Additional "in" operator for fields being lists of strings

[Marcin Szewczyk]

Hi,

I would like to propose an additional "in" operator which would treat
field's string value as a space-separated list and check if the
specified token is present.

I know that fully normalized relational databases would look like this:

    Device: plumbus
    Tag: dinglebop
    Tag: fleeb
    Tag: plubus
    Tag: grumbo

But it might be quicker to use when constructed in the following manner:

    Device: plumbus
    Tags: dinglebop fleeb plubus grumbo

Relational databases support non-scalar types like arrays[1], XML or
JSON. AFAIK arrays are used for performance reasons to save on JOINs.
Here I propose the operator just as a usability enhancement.

The '"fleeb" in Tags' expression seems a bit more expressive and
straightforward than similarly working 'Tag ~ "\bfleeb\b"' or 'Tag ~
"\<fleeb\>"'.

Furthermore, the array structure makes it easy to select records with
fields containing two specified values at the same time. Without an
array it seems to require piping two `recsel` processes[2]. With an
array and the "in" operator one could write:

    '"fleeb" in Tags && "grumbo" in Tags'

Proposed patch attached.


[1]: https://www.postgresql.org/docs/current/arrays.html
[2]: https://lists.gnu.org/archive/html/bug-recutils/2017-04/msg00001.html

-- 
Marcin Szewczyk
http://wodny.org

0001-add-the-in-operator.patch
Description: Text Data