How to use omit with Ansible and avoid any errors?

问题

I tried to use omit with an expression like this:

id: "{{ openstack_networks.id | default(omit) }}"

But it seems that it keeps failing with an exception when openstack_networks variable is not defined.

What is the correct way to write this jinja2 filter?

I want to omit the parameter in case openstack_networks.id does not exists.

回答1:

Not super elegant, but 100% working solution to handle keys of possibly undefined parent dicts:

id: "{{ (openstack_networks | default({})).id | default(omit) }}"

This will give you omit if openstack_networks is defined but has no id key or if openstack_networks is undefined.

回答2:

Interestingly enough, Ansible will take something that reads like plain English:

id: "{{ omit if openstack_networks.id is not defined or openstack_networks.id }}"

The benefit here is that there are no additional parentheses.

来源：https://stackoverflow.com/questions/41725555/how-to-use-omit-with-ansible-and-avoid-any-errors