Default parameters in nested yaml pipeline Azure DevOps - azure-devops

Question

I have multiple resusable yaml templates to build my project using Azure DevOps. I want to let the default template values when I don't want to override it. The problem I have is when I nest multiple templates, it's not working as I expected, here is an example of my issue:
task_template1.yml:
parameters:
foo: 'data'
steps:
- task: Bash#3
inputs:
targetType: 'inline'
script: echo ${{ parameters.foo }}
Inside a job_template.yml I call this task_template1.yml like this:
job_template.yml:
parameters:
fooTemplate: 'data'
jobs:
- job:
steps:
- template: task_template1.yml
parameters:
${{ if variables[parameters.fooTemplate] }}:
foo: ${{ parameters.fooTemplate }}
And then my global template:
stage_build.yml:
stages:
- stage: Build
jobs:
- template: job_template.yml
parameters:
fooTemplate: 'hello'
So in this case, by default I expect that my variable fooTemplate will set the value of the variable foo inside my task_template1.yml to hello because I specify it.
But it's not the case, because it looks like ${{ if variables[parameters.fooTemplate] }}: is evaluated before the build start so foo is set to data instead of hello. Conversely if I would like to keep the default value of fooTemplate (data) I just want to not specify it like this:
stages:
- stage: Build
jobs:
- template: job_template.yml
It looks like a problem of nested templates. How can I do to fit this two rules? Feel free to ask me some more details if needed.
EDIT:
I always have this message : 'foo has no value: undefined'
Other case that I have, instead of a simple parameter:
parameters:
foo:'data'
foo1:'data1'
steps:
- task: Bash#3
inputs:
targetType: 'inline'
script: echo ${{ parameters.foo }}
So for the job I have:
parameters:
fooTemplate:
foo:'data'
foo1:'data1'
jobs:
- job:
steps:
- template: task_template1.yml
parameters:
${{ if ne(parameters.fooTemplate.foo, ' ') }}:
foo: ${{ parameters.fooTemplate.foo }}
${{ if ne(parameters.fooTemplate.foo1, ' ') }}:
foo: ${{ parameters.fooTemplate.foo1 }}
And then same case if I don't specify the foo and foo1 value I have the undefined error, instead of taking the default values:
stages:
- stage: Build
jobs:
- template: job_template.yml

Answer 1

I think something is wrong with your syntax here:
parameters:
${{ if variables[parameters.fooTemplate] }}:
foo: ${{ parameters.fooTemplate }}
Try this way(according to this):
parameters:
${{ if eq(parameters.fooTemplate, true) }}:
foo: ${{ parameters.fooTemplate }}
It works on my side.
Notes:
You can have something like this:
parameters:
fooTemplate: 'data'
jobs:
- job:
steps:
- template: task_template1.yml
parameters:
${{ if ne(parameters.fooTemplate, ' ') }}:
foo: ${{ parameters.fooTemplate }}
Now if you specify 'hello' in stage_build.yml, the task_template1.yml will output hello. And if you don't specify the parameter in stage_build.yml like this:
pool:
vmImage: 'ubuntu-latest'
jobs:
- template: job_template.yml
It will output the default data. Here're more details about Expressions and Conditions.