Re: Merge of data containers

Stefan Skoglund <[email protected]> writes:

Reading the docs for `mapdata()', I was a bit surprised that `mapdata(
"json", '{ "stats": $(this.v) }' , "ifs")' works.

,----
| bundle agent __main__
| {
|   vars:
|       "a"
|         data => parsejson('{ "ifname": "lo"}');
|       "b"
|         data => parsejson('{ "ifname": "enp1"}');
|
|       "ifs"
|         slist => { "a", "b"};
|
|       "a_b"
|         data => mapdata( "json", '{ "status": $(this.v) }' , "ifs");
| }
`----

,----
| Variable name                            Variable value                                               Meta tags                                Comment
| default:main.a                           {"ifname":"lo"}                                              source=promise
| default:main.a_b                         [{"status":{"ifname":"lo"}},{"status":{"ifname":"enp1"}}]    source=promise
| default:main.b                           {"ifname":"enp1"}                                            source=promise
| default:main.ifs                          {"a","b"}                                                   source=promise
`----


The last parameter to `mapdata()' is expected to be an array or data
container:

,----
| bundle agent __main__
| {
|   vars:
|       "a"
|         data => parsejson('{ "ifname": "lo"}');
|       "b"
|         data => parsejson('{ "ifname": "enp1"}');
|
|       "ifs"
|         data => '[ "a", "b" ]';
|
|       "a_b"
|         data => mapdata( "json", '{ "status": $(this.v) }' , "ifs");
| }
`----

,----
| Variable name                            Variable value                                               Meta tags                                Comment
| default:main.a                           {"ifname":"lo"}                                              source=promise
| default:main.a_b                         [{"status":{"ifname":"lo"}},{"status":{"ifname":"enp1"}}]    source=promise
| default:main.b                           {"ifname":"enp1"}                                            source=promise
| default:main.ifs                         ["a","b"]                                                    source=promise
`----


`$(this.v)' should expand to `a' and `b'.

But then I remembered that you can wrap naked variable names. You can
achieve similar result with `mergedata()' explicitly

,----
| bundle agent __main__
| {
|   vars:
|       "a"
|         data => parsejson('{ "ifname": "lo"}');
|       "b"
|         data => parsejson('{ "ifname": "enp1"}');
|
|       "a_b"
|         data => mergedata( '[{ "status": a }]' , '[{ "status": b }]' );
| }
`----

,----
| Variable name                            Variable value                                               Meta tags                                Comment
| default:main.a                           {"ifname":"lo"}                                              source=promise
| default:main.a_b                         [{"status":{"ifname":"lo"}},{"status":{"ifname":"enp1"}}]    source=promise
| default:main.b                           {"ifname":"enp1"}                                            source=promise
`----


      So how to load data from multiple datacontainers into a json
      array in a data container ?

If your trying to merge data containers, remember that objects will
overwrite. If you merge `{ "ifname": "lo"}' and `{ "ifname": "enp1"}'
whichever is merged last will win.

,----
| bundle agent __main__
| {
|   vars:
|       "a"
|         data => parsejson('{ "ifname": "lo"}');
|       "b"
|         data => parsejson('{ "ifname": "enp1"}');
|
|       # Here b will win since it's merged last
|       "a_b"
|         data => mergedata( a, b );
|
|       # Here a will win since it's merged last
|       "b_a"
|         data => mergedata( b, a );
| }
`----

,----
| Variable name                            Variable value                                               Meta tags                                Comment
| default:main.a                           {"ifname":"lo"}                                              source=promise
| default:main.a_b                         {"ifname":"enp1"}                                            source=promise
| default:main.b                           {"ifname":"enp1"}                                            source=promise
| default:main.b_a                         {"ifname":"lo"}                                              source=promise
`----


When you merge arrays, they will merge. This is the behavior you saw
when you used mapdata.

You could potentially use `variablesmatching_as_data()'.

,----
| bundle agent __main__
| {
|   vars:
|       "a"
|         data => parsejson('{ "ifname": "lo"}'),
|         meta => { "tag" };
|       "b"
|         data => parsejson('{ "ifname": "enp1"}'),
|         meta => { "tag" };
|
|       "tagged_with_tag"
|         data => variablesmatching_as_data( ".*", "tag" );
|
|       "tagged_with_tag_i" slist => getindices( a_b );
| }
`----

,----
| Variable name                            Variable value                                               Meta tags                                Comment
| default:main.a                           {"ifname":"lo"}                                              source=promise,tag
| default:main.b                           {"ifname":"enp1"}                                            source=promise,tag
| default:main.tagged_with_tag             {"default:main.a":{"ifname":"lo"},"default:main.b":{"ifname":"enp1"}} source=promise
| default:main.tagged_with_tag_i                                                                        source=promise
`----


You might be better off using a module to do all the json munging and
simply return that back to CFEngine.

-- Nick Anderson | Doer of Things | (+1) 785-550-1767 |
<https://northern.tech>

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