My personal opinion would be no. We should not add another filter when
`json_query` or native jinja2 filters can produce the same results.
On Wed, Jan 30, 2019 at 4:23 PM Alex Willmer <a...@moreati.org.uk> wrote:
> *Abstract*
> I would like to contribute a new jq() filter to Ansible, exposing the jq
> expression language. This would complement the existing json_query()
> filter, based on jmespath expressions. I wanted to see if such a filter
> would be welcome, either as PR to Ansible itself, or a third party module
> through Ansible Galaxy
>
> *Background*
> jq is an expression language used for filtering and transforming JSON
> data. It is mostly commonly used through the jq command, to filter JSON in
> a pipeline.
>
> Examples of jq command
> $ echo '[{"x":1, "y":2}, {"x":11}]' | jq .[0].x
> 1
>
> $ echo '[{"x":1, "y":2}, {"x":11}]' | jq '[.[] | .x]'
> [
> 1,
> 11
> ]
>
> *Motivation*
> There are some operations expressible with jq that are not expressible
> with jmespath. The one I have encountered is producing a flat list of
> objects, from a list of objects each with a nested list of something. e.g.
>
> $ cat databases.json
> [
> {"db": "a", "users": [{"name": "alice"}, {"name": "alex"}]},
> {"db": "b", "users": [{"name": "bob"}, {"name": "brienne"}]}
> ]
> $ cat databases.json | jq '. | map({db, name: .users[].name})'
> [
> {
> "db": "a",
> "name": "alice"
> },
> {
> "db": "a",
> "name": "alex"
> },
> {
> "db": "b",
> "name": "bob"
> },
> {
> "db": "b",
> "name": "brienne"
> }
> ]
>
> *Design*
> The filter would be invoked in a similar manner to the json_query() filter
>
> Mockup:
> $ ansible localhost -mdebug -a'{{ [{"x":1, "y":2}, {"x":11}] | jq('[.[] |
> .x]') }}'
> localhost | SUCCESS => {
> "msg": [
> 1,
> 11
> ]
> }
>
> Initially jq features such as jq arguments/variables would be excluded.
>
> *Implementation*
> The filter would expose one of the existing Python bindings to libjq, the
> C library on which the jq command is built.
>
> *Alternatives*
> The json_query() filter (based on jmespath) covers much of the same
> functionality as jq. The few cases where jmespath cannot implement a
> particular operation alone could be overcome by supplementing with other
> filters, e.g.
>
> {{ databases | subelements('users')
> | to_json | from_json
> | json_query('[*].{db: [0].db, name: [1].name}')
> }}
>
> would produce the same result as the proposed {{ databases | jq('. |
> map({db, name: .users[].name})') }}.
>
> References
> https://stedolan.github.io/jq/
>
> https://docs.ansible.com/ansible/latest/user_guide/playbooks_filters.html#json-query-filter
>
> https://stackoverflow.com/questions/54160360/jmespath-expression-to-flatten-array-of-objects-each-with-nested-arrays-of-obje
> https://jqplay.org/s/5YHjzcspb5
> https://pypi.org/project/jq/
> https://pypi.org/project/pyjq/
>
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--
Matt Martz
@sivel
sivel.net
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