mirror of https://github.com/ansible/ansible.git
start of 'data manipulation' examples (#46979)
Co-authored-by: Klaus Frank <agowa338@users.noreply.github.com> Co-authored-by: Felix Fontein <felix@fontein.de> Co-authored-by: Abhijeet Kasurde <akasurde@redhat.com>pull/71174/head
Brian Coca
4 years ago
committed by
GitHub
parent
4f54fb8d43
commit
f46b124d65
@ -0,0 +1,243 @@
|
||||
.. _complex_data_manipulation:
|
||||
|
||||
Data manipulation
|
||||
#########################
|
||||
|
||||
In many cases, you need to do some complex operation with your variables, while Ansible is not recommended as a data processing/manipulation tool, you can use the existing Jinja2 templating in conjunction with the many added Ansible filters, lookups and tests to do some very complex transformations.
|
||||
|
||||
Let's start with a quick definition of each type of plugin:
|
||||
- lookups: Mainly used to query 'external data', in Ansible these were the primary part of loops using the ``with_<lookup>`` construct, but they can be used independently to return data for processing. They normally return a list due to their primary function in loops as mentioned previously. Used with the ``lookup`` or ``query`` Jinja2 operators.
|
||||
- filters: used to change/transform data, used with the ``|`` Jinja2 operator.
|
||||
- tests: used to validate data, used with the ``is`` Jinja2 operator.
|
||||
|
||||
.. _note:
|
||||
* Some tests and filters are provided directly by Jinja2, so their availability depends on the Jinja2 version, not Ansible.
|
||||
|
||||
.. _for_loops_or_list_comprehensions:
|
||||
|
||||
Loops and list comprehensions
|
||||
=============================
|
||||
|
||||
Most programming languages have loops (``for``, ``while``, etc.) and list comprehensions to do transformations on lists including lists of objects. Jinja2 has a few filters that provide this functionality: ``map``, ``select``, ``reject``, ``selectattr``, ``rejectattr``.
|
||||
|
||||
- map: this is a basic for loop that just allows you to change every item in a list, using the 'attribute' keyword you can do the transformation based on attributes of the list elements.
|
||||
- select/reject: this is a for loop with a condition, that allows you to create a subset of a list that matches (or not) based on the result of the condition.
|
||||
- selectattr/rejectattr: very similar to the above but it uses a specific attribute of the list elements for the conditional statement.
|
||||
|
||||
|
||||
.. _keys_from_dict_matching_list:
|
||||
|
||||
Extract keys from a dictionary matching elements from a list
|
||||
------------------------------------------------------------
|
||||
|
||||
The Python equivalent code would be:
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
chains = [1, 2]
|
||||
for chain in chains:
|
||||
for config in chains_config[chain]['configs']:
|
||||
print(config['type'])
|
||||
|
||||
There are several ways to do it in Ansible, this is just one example:
|
||||
|
||||
.. code-block:: YAML+Jinja
|
||||
:emphasize-lines: 3
|
||||
:caption: Way to extract matching keys from a list of dictionaries
|
||||
|
||||
tasks:
|
||||
- name: Show extracted list of keys from a list of dictionaries
|
||||
debug: msg="{{ chains | map('extract', chains_config) | map(attribute='configs') | flatten | map(attribute='type') | flatten }}"
|
||||
vars:
|
||||
chains: [1, 2]
|
||||
chains_config:
|
||||
1:
|
||||
foo: bar
|
||||
configs:
|
||||
- type: routed
|
||||
version: 0.1
|
||||
- type: bridged
|
||||
version: 0.2
|
||||
2:
|
||||
foo: baz
|
||||
configs:
|
||||
- type: routed
|
||||
version: 1.0
|
||||
- type: bridged
|
||||
version: 1.1
|
||||
|
||||
|
||||
.. code-block:: ansible-output
|
||||
:caption: Results of debug task, a list with the extracted keys
|
||||
|
||||
ok: [localhost] => {
|
||||
"msg": [
|
||||
"routed",
|
||||
"bridged",
|
||||
"routed",
|
||||
"bridged"
|
||||
]
|
||||
}
|
||||
|
||||
|
||||
.. _find_mount_point:
|
||||
|
||||
Find mount point
|
||||
----------------
|
||||
|
||||
In this case, we want to find the mount point for a given path across our machines, since we already collect mount facts, we can use the following:
|
||||
|
||||
.. code-block:: YAML+Jinja
|
||||
:caption: Use selectattr to filter mounts into list I can then sort and select the last from
|
||||
:emphasize-lines: 7
|
||||
|
||||
- hosts: all
|
||||
gather_facts: True
|
||||
vars:
|
||||
path: /var/lib/cache
|
||||
tasks:
|
||||
- name: The mount point for {{path}}, found using the Ansible mount facts, [-1] is the same as the 'last' filter
|
||||
debug: msg="{{(ansible_facts.mounts | selectattr('mount', 'in', path) | list | sort(attribute='mount'))[-1]['mount']}}"
|
||||
|
||||
|
||||
|
||||
Omit elements from a list
|
||||
-------------------------
|
||||
|
||||
The special ``omit`` variable ONLY works with module options, but we can still use it in other ways as an identifier to tailor a list of elements:
|
||||
|
||||
.. code-block:: YAML+Jinja
|
||||
:caption: Inline list filtering when feeding a module option
|
||||
:emphasize-lines: 3, 7
|
||||
|
||||
- name: enable a list of Windows features, by name
|
||||
set_fact:
|
||||
win_feature_list: "{{ namestuff | reject('equalto', omit) | list }}"
|
||||
vars:
|
||||
namestuff:
|
||||
- "{{ (fs_installed_smb_v1 | default(False)) | ternary(omit, 'FS-SMB1') }}"
|
||||
- "foo"
|
||||
- "bar"
|
||||
|
||||
|
||||
Another way is to avoid adding elements to the list in the first place, so you can just use it directly:
|
||||
|
||||
.. code-block:: YAML+Jinja
|
||||
:caption: Using set_fact in a loop to increment a list conditionally
|
||||
:emphasize-lines: 3, 4, 6
|
||||
|
||||
- name: build unique list with some items conditionally omittted
|
||||
set_fact:
|
||||
namestuff: ' {{ (namestuff | default([])) | union([item]) }}'
|
||||
when: item != omit
|
||||
loop:
|
||||
- "{{ (fs_installed_smb_v1 | default(False)) | ternary(omit, 'FS-SMB1') }}"
|
||||
- "foo"
|
||||
- "bar"
|
||||
|
||||
|
||||
.. _complex_type_transfomations:
|
||||
|
||||
Complex Type transformations
|
||||
=============================
|
||||
|
||||
Jinja provides filters for simple data type transformations (``int``, ``bool``, etc), but when you want to transform data structures things are not as easy.
|
||||
You can use loops and list comprehensions as shown above to help, also other filters and lookups can be chained and leveraged to achieve more complex transformations.
|
||||
|
||||
|
||||
.. _create_dictionary_from_list:
|
||||
|
||||
Create dictionary from list
|
||||
---------------------------
|
||||
|
||||
In most languages it is easy to create a dictionary (a.k.a. map/associative array/hash etc.) from a list of pairs, in Ansible there are a couple of ways to do it and the best one for you might depend on the source of your data.
|
||||
|
||||
|
||||
These example produces ``{"a": "b", "c": "d"}``
|
||||
|
||||
.. code-block:: YAML+Jinja
|
||||
:caption: Simple list to dict by assuming the list is [key, value , key, value, ...]
|
||||
|
||||
vars:
|
||||
single_list: [ 'a', 'b', 'c', 'd' ]
|
||||
mydict: "{{ dict(single_list) | slice(2) | list }}"
|
||||
|
||||
|
||||
.. code-block:: YAML+Jinja
|
||||
:caption: It is simpler when we have a list of pairs:
|
||||
|
||||
vars:
|
||||
list_of_pairs: [ ['a', 'b'], ['c', 'd'] ]
|
||||
mydict: "{{ dict(list_of_pairs) }}"
|
||||
|
||||
Both end up being the same thing, with the ``slice(2) | list`` transforming ``single_list`` to the same structure as ``list_of_pairs``.
|
||||
|
||||
|
||||
|
||||
A bit more complex, using ``set_fact`` and a ``loop`` to create/update a dictionary with key value pairs from 2 lists:
|
||||
|
||||
.. code-block:: YAML+Jinja
|
||||
:caption: Using set_fact to create a dictionary from a set of lists
|
||||
:emphasize-lines: 3, 4
|
||||
|
||||
- name: Uses 'combine' to update the dictionary and 'zip' to make pairs of both lists
|
||||
set_fact:
|
||||
mydict: "{{ mydict | default({}) | combine({item[0]: item[1]}) }}"
|
||||
loop: "{{ (keys | zip(values)) | list }}"
|
||||
vars:
|
||||
keys:
|
||||
- foo
|
||||
- var
|
||||
- bar
|
||||
values:
|
||||
- a
|
||||
- b
|
||||
- c
|
||||
|
||||
This results in ``{"foo": "a", "var": "b", "bar": "c"}``.
|
||||
|
||||
|
||||
You can even combine these simple examples with other filters and lookups to create a dictionary dynamically by matching patterns to variable names:
|
||||
|
||||
.. code-block:: YAML+Jinja
|
||||
:caption: Using 'vars' to define dictionary from a set of lists without needing a task
|
||||
|
||||
vars:
|
||||
myvarnames: "{{ q('varnames', '^my') }}"
|
||||
mydict: "{{ dict(myvarnames | zip(q('vars', *myvarnames))) }}"
|
||||
|
||||
A quick explanation, since there is a lot to unpack from these two lines:
|
||||
|
||||
- The ``varnames`` lookup returns a list of variables that match "begin with ``my``".
|
||||
- Then feeding the list from the previous step into the ``vars`` lookup to get the list of values.
|
||||
The ``*`` is used to 'dereference the list' (a pythonism that works in Jinja), otherwise it would take the list as a single argument.
|
||||
- Both lists get passed to the ``zip`` filter to pair them off into a unified list (key, value, key2, value2, ...).
|
||||
- The dict function then takes this 'list of pairs' to create the dictionary.
|
||||
|
||||
|
||||
An example on how to use facts to find a host's data that meets condition X:
|
||||
|
||||
|
||||
.. code-block:: YAML+Jinja
|
||||
|
||||
vars:
|
||||
uptime_of_host_most_recently_rebooted: "{{ansible_play_hosts_all | map('extract', hostvars, 'ansible_uptime_seconds') | sort | first}}"
|
||||
|
||||
|
||||
Using an example from @zoradache on reddit, to show the 'uptime in days/hours/minutes' (assumes facts where gathered).
|
||||
https://www.reddit.com/r/ansible/comments/gj5a93/trying_to_get_uptime_from_seconds/fqj2qr3/
|
||||
|
||||
.. code-block:: YAML+Jinja
|
||||
|
||||
- debug:
|
||||
msg: Timedelta {{ now() - now().fromtimestamp(now(fmt='%s') | int - ansible_uptime_seconds) }}
|
||||
|
||||
|
||||
.. seealso::
|
||||
|
||||
:doc:`playbooks_filters`
|
||||
Jinja2 filters included with Ansible
|
||||
:doc:`playbooks_tests`
|
||||
Jinja2 tests included with Ansible
|
||||
`Jinja2 Docs <http://jinja.pocoo.org/docs/>`_
|
||||
Jinja2 documentation, includes lists for core filters and tests
|
||||
Loading…
Reference in New Issue