Building a properties file with Ansible where the Property should not be added if the value doesn't exist

Question

I am trying to build a property file with mandatory and optional properties in Ansible with templating.

I want each essentially-static string (each optional property name) to show up only if the associated property value exists (from an Ansible variable)

Right now, my ansible template looks like this:

# Mandatory Properties
ManProperty1={{ ManProperty1_value }}
ManProperty2={{ ManProperty2_value }}
# Optional Properties
OptProperty1={{ OptProperty1_value }}
OptProperty2={{ OptProperty2_value }}

But the application itself has hardcoded values for all the optional properties, and I only want a "property=value" line to get written to the properties file from the template if the associated variable exists.

So continuing with the template above, if I set for environment X (group_vars)

ManProperty1_value = myManValue1
ManProperty2_value = myManValue2
OptProperty1_value = myOptValue1

but do not set

OptProperty2_value

My desired output of the template to the deployed file is:

# Mandatory Properties
ManProperty1=myManValue1
ManProperty2=myManValue2
# Optional Properties
OptProperty1=myOptValue1

There must be a better solution in Ansible to this. The closest I found was ansible filtering, but I couldn't find anything in there related to show/hide of template text.

Final note: I do have a hackish backup solution - I take each line of property=value and make the variable equal the entire string. But this feels like it's completely missing the point of a template with so much static text stored in variables.

Answer 1

^{Firstly, this is not an Ansible problem, it's a question how to use Jinja2 templating language (and as a strictly programming question, it should be asked on StackOverflow not ServerFault).}

Head to Jinja2 documentation on if statement and you will find an exact example for your case:

The if statement in Jinja is comparable with the Python if statement. In the simplest form, you can use it to test if a variable is defined, not empty and not false.

Here's an example how you should customise it:

{% if OptProperty2_value %}OptProperty2={{ OptProperty2_value }}{% endif %}