JMESPath filter for elements with nested values starting with certain string

Question

I have the following JSON structure:

[
    {
        "stack": [
            "datasync"
        ],
        "env": [
            "dev",
            "test"
        ],
        "runOnBranch": [
            "feature/",
            "bugfix/",
            "develop"
        ]
    },
    {
        "stack": [
            "datasync"
        ],
        "env": [
            "val",
            "prod"
        ],
        "runOnBranch": [
            "main"
        ]
    }
]

And I would like to filter the list based on if a given string starts with one of the strings defined in the runOnBranch attribute.

My best guess so far doesn't work:

[?runOnBranch.starts_with(@, `feature/`) == `true`]

The error I get is:

"Search parse error": TypeError: starts_with() expected argument 1 to be type 2 but received type 3 instead.

The result I would like to get is:

[
    {
        "stack": [
            "datasync"
        ],
        "env": [
            "dev",
            "test"
        ],
        "runOnBranch": [
            "feature/",
            "bugfix/",
            "develop"
        ]
    }
]

What am I missing?

Your attempt does not work because `starts_with` needs a string (`boolean starts_with(string $subject, string $prefix)`), while you are passing an array to it. — β.εηοιτ.βε, Sep 02 '22 at 17:56

β.εηοιτ.βε · Accepted Answer · 2022-09-03T12:37:23.267

In order to assess that there is one element in the array that starts with something you will need to:

assess each string in the array, effectively creating a list of boolean, so, with starts_with but targeting each string, not the whole array:
```
runOnBranch[].starts_with(@, `feature/`),
```
assess that there is at least one true value contained in the resulting array, with the help of the contains function
```
contains(runOnBranch[].starts_with(@, `feature/`), `true`)
```
and finally put all this in your filter

So, we end with the query:

[?contains(runOnBranch[].starts_with(@, `feature/`), `true`)]

Which yields:

[
  {
    "stack": [
      "datasync"
    ],
    "env": [
      "dev",
      "test"
    ],
    "runOnBranch": [
      "feature/",
      "bugfix/",
      "develop"
    ]
  }
]

And to be more coherent in notation, this can also be written as:

[?(runOnBranch[].starts_with(@, `feature/`)).contains(@, `true`)]

Side note: simplify those kind of filter:

[?runOnBranch.starts_with(@, `feature/`) == `true`]

to

[?runOnBranch.starts_with(@, `feature/`)]

as starts_with already returns a boolean, as documented in the function signature:

boolean starts_with(string $subject, string $prefix)

^{Source: https://jmespath.org/specification.html#starts-with}

What can I say... great explanation! Thanks a ton! – WolfgangM Sep 03 '22 at 08:47 — WolfgangM, Sep 03 '22 at 08:47

Vladimir Botka · Answer 2 · 2022-09-04T03:48:13.410

Q: "Filter the list on attribute's runOnBranch any item starts with a given string."

A: Put the below declarations into the vars

_query: '[?runOnBranch[?starts_with(@, `feature/`)]]'
result: "{{ data|json_query(_query) }}"

gives

result:
  - env: [dev, test]
    runOnBranch: [feature/, bugfix/, develop]
    stack: [datasync]

^{Example of a complete playbook for testing
- hosts: localhost

vars:

data:
- env: [dev, test]
runOnBranch: [feature/, bugfix/, develop]
stack: [datasync]
- env: [val, prod]
runOnBranch: [main]
stack: [datasync]

_query: '[?runOnBranch[?starts_with(@, `feature/`)]]'
result: "{{ data|json_query(_query) }}"

tasks:

- debug:
var: result|to_yaml

You can put the string into a variable. For example,
pattern: feature/
_query: '[?runOnBranch[?starts_with(@, `{{ pattern }}`)]]'

Then, you can override the string on the command line. For example,
shell> ansible-playbook playbook.yml -e pattern=ma

PLAY [localhost] *****************************************************************************

TASK [debug] *********************************************************************************
ok: [localhost] =>
feature|to_yaml: |-
- env: [val, prod]
runOnBranch: [main]
stack: [datasync]

PLAY RECAP ***********************************************************************************
localhost: ok=1 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0}

JMESPath filter for elements with nested values starting with certain string

2 Answers2