Re: remove specified key from data container

      Hi all, I like data containers with json. I have a simple
      data container

      '{ "name1": "aaaa", "name2": "bbbb", "name3": "cccc" }'

      and I don't know how to remove the key 'name2' from the data
      container.

      I tried a difference function but its returns only slist,
      not data container. What is the best practice? Is posible
      using json_pipe, how?

      Thanks Michal Svamberg

Hi Michal,

I can think of a couple ways of doing it. The first thing that came to
mind was leveraging a classic array. This is a pattern that I have used
for a long time. I still find it useful quite often. Another method that
came to mind was to leverage `jq' via `mapdata()' using the `json_pipe'
interpretation as you noted.

Here is an example:

,----
| bundle agent __main__
| {
|   vars:
|       "original" data => '{ "name1": "aaaa", "name2": "bbbb", "name3": "cccc" }';
| 
|       # Method 0, build up a classic array using iteration
|       "_original_keys" slist => getindices( original );
|       "_a[$(_original_keys)]"
|         string => "$(original[$(_original_keys)])",
|         unless => strcmp( "name2", "$(_original_keys)" );
|       "method_0" data => mergedata( "_a" );
| 
|       # Method 1, jq via json_pipe
|       # mapdata returns a json array, so we use parsejson(nth(0)) to pick out the dict
|       "_method_1_json_array"
|         data => mapdata( "json_pipe",
|                          `$(def.jq) 'del(.name2)'`,
|                          original);
|       "method_1" data => mergedata( "_method_1_json_array[0]" );
| }
`----
Listing 1: Example Policy

,----
| # cf-agent --no-lock --log-level info --show-evaluated-vars=default:main\\. --file /tmp/example.cf
| Variable name                            Variable value                                               Meta tags                                Comment                                 
| default:main._a[name1]                   aaaa                                                         source=promise                                                                   
| default:main._a[name3]                   cccc                                                         source=promise                                                                   
| default:main._method_1_json_array        [{"name1":"aaaa","name3":"cccc"}]                            source=promise                                                                   
| default:main._original_keys               {"name1","name2","name3"}                                   source=promise                                                                   
| default:main.method_0                    {"name1":"aaaa","name3":"cccc"}                              source=promise                                                                   
| default:main.method_1                    {"name1":"aaaa","name3":"cccc"}                              source=promise                                                                   
| default:main.original                    {"name1":"aaaa","name2":"bbbb","name3":"cccc"}               source=promise                                                                   
`----


I don't know that I have any firm position on what is /best/. I think
both methodologies have their own merits. The classic array generator
works anywhere CFEngine works. `mapdata()' using the `json_pipe'
interpretationrequires some external utility like jq which may not be
universally available.

Hope this helps ...

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