How do I set Azure Pipelines triggers on condition directly from the .yml file?

Question

I tried with

trigger:
  branches:
    include:
      ${{ if flavour == 'staging' }}:
      - staging
      ${{ else }}:
      - master

But Azure returns the following error:

/devops/build&upload.yml (Line: 4, Col: 7): A mapping was not expected

The result I want to achieve is to have triggers depending on the value of the flavour variable. It can be set to staging, in which case I want the value of include to be staging, or it can have other values, in which case I want the include to have the value master.

Answer 1

Trigger blocks can't contain variables or template expressions.

You can check the link for the details.

If you would triggers depending on the value of the flavour variable, as an alternative, you can:

1. Use UI trigger to override the yaml trigger, as if you use trigger in yaml, it could have different triggers defined between branches.

2. Use a new pipeline, determine the branch according to the variable flavour value, then use rest api to get the pipeline definition, and update the trigger to your expectation.

The new yaml sample:

pool:
  vmImage: ubuntu-latest

variables:
  - name: flavour
    value: staging 

steps:
- ${{ if eq(variables.flavour, 'staging') }}:
  - script: echo "##vso[task.setvariable variable=branchToUse;]staging"
- ${{ else }}:
  - script: echo "##vso[task.setvariable variable=branchToUse;]main"

- powershell: |
    $Organization = "org"
    $Project = "project"
    $PipelineId = "pipelineid"
    $header = @{Authorization = "Bearer $(System.AccessToken)"}

    $request = "https://dev.azure.com/$($Organization)/$($Project)/_apis/build/definitions/$($PipelineId)?api-version=7.1-preview.7"
    echo $request   # check the request url
    $json = Invoke-WebRequest -Uri $request -Method Get -Headers $header -ContentType "application/json" | ConvertFrom-Json

    # Set Branch Filter
    $defaultBranch = "$(branchToUse)"
    $branchFilters = @("+refs/heads/$($defaultBranch)")

    $json.triggers[0].branchFilters = $branchFilters

    echo $json.triggers[0].branchFilters   # check the branch value

    # Convert PSObject back to Json
    $json = $json | ConvertTo-Json -Depth 100

    # Update Pipeline
    $request = "https://dev.azure.com/$($Organization)/$($Project)/_apis/build/definitions/$($PipelineId)?api-version=7.1-preview.7"
    $result = Invoke-RestMethod -Uri $request -Method Put -ContentType "application/json" -Headers $header -Body $json

The branch updated:

Here i used system.accestoken in the rest api, please make sure on target pipeline, the build service account has edit pipeline permission otherwise the rest api will be denied.