Ansible - How To Use Selectattr With Yaml Of Different Keys

im pulling my hairs trying to do a simple thing (i thought it should be easy) with parsing a yaml and filtering for some key in Ansible. My yaml file looks like this: --- - vm: 'v

Solution 1:

More precisely, it is expecting all dicts in the list to have the attribute you are selecting on.

It is not 100% true for all filter functions, to select objects by an attribute not defined by all elements:

{{ test_var | selectattr('vm','defined') |selectattr('vm','equalto','vm1') | list }} 

Solution 2:

Is selectattr filter expecting all the dicts in the list to have the same keys?

More precisely, it is expecting all dicts in the list to have the attribute you are selecting on. If not all dict in the list have it, you will have to first filter out the items where it is not defined. This can be done with selectattr as well. (thanks @Randy for making this clearer since my initial answer).

In your situation, the json_query filter (which implements jmespath) can also do the job in sometimes a more compact manner. But it is not a core filter and requires to have the community.general collection installed.

Here are a few examples taken from your above requirements solved with both core filters and json_query solutions.

The playbook:

----name:"Filter data with core filters or json query"hosts:"localhost"gather_facts:falsevars:# Your initial data on a single line for legibilitytest_var: [{"vm":"vm1"},{"ip":"10.10.10.1"},{"vm":"vm2","ip":"10.10.10.2"},{"test_vm":"something","process_1":"X","process_2":"Y","process_3":"Z"},{"another_vm":"something_other"}]

  tasks:-name:Getobjectshavingvm==vm1vars:msg:|-
          With core filters: {{ test_var | selectattr('vm', 'defined') | selectattr('vm', '==', 'vm1') | list }}
          With json_query: {{ test_var | json_query("[?vm=='vm1']") | list }}
debug:msg:"{{ msg.split('\n') }}"-name:Getallobjectshavingvmattributevars:msg:|-
          With core filters: {{ test_var | selectattr('vm', 'defined') | list }}
          With json_query: {{ test_var | json_query("[?vm]") | list }}
debug:msg:"{{ msg.split('\n') }}"-name:Getallobjectshavingprocess_2attributevars:msg:|-
          With core filters: {{ test_var | selectattr('process_2', 'defined') | list }}
          With json_query: {{ test_var | json_query("[?process_2]") | list }}
debug:msg:"{{ msg.split('\n') }}"-name:Getonlyalistofprocess_2attributesvars:msg:|-
          With core filters: {{ test_var | selectattr('process_2', 'defined') | map(attribute='process_2') | list }}
          With json_query: {{ test_var | json_query("[].process_2") | list }}
debug:msg:"{{ msg.split('\n') }}"

which gives:

PLAY [Filter data with core filters or json query] *********************************************************************

TASK [Get objects having vm==vm1] *********************************************************************
ok: [localhost] => {
    "msg": [
        "With core filters: [{'vm': 'vm1', 'ip': '10.10.10.1'}]",
        "With json_query: [{'vm': 'vm1', 'ip': '10.10.10.1'}]"
    ]
}

TASK [Get all objects having vm attribute] *********************************************************************
ok: [localhost] => {
    "msg": [
        "With core filters: [{'vm': 'vm1', 'ip': '10.10.10.1'}, {'vm': 'vm2', 'ip': '10.10.10.2'}]",
        "With json_query: [{'vm': 'vm1', 'ip': '10.10.10.1'}, {'vm': 'vm2', 'ip': '10.10.10.2'}]"
    ]
}

TASK [Get all objects having process_2 attribute] *********************************************************************
ok: [localhost] => {
    "msg": [
        "With core filters: [{'test_vm': 'something', 'process_1': 'X', 'process_2': 'Y', 'process_3': 'Z'}]",
        "With json_query: [{'test_vm': 'something', 'process_1': 'X', 'process_2': 'Y', 'process_3': 'Z'}]"
    ]
}

TASK [Get only a list of process_2 attributes] *********************************************************************
ok: [localhost] => {
    "msg": [
        "With core filters: ['Y']",
        "With json_query: ['Y']"
    ]
}

PLAY RECAP *********************************************************************
localhost                  : ok=4    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0