Conditionally running a second job in a GitHub Actions workflow#

My simonwillisonblog-backup workflow periodically creates a JSON backup of my blog’s PostgreSQL database, using db-to-sqlite and sqlite-diffable. It then commits any changes back to the repo using this pattern:

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    - name: Commit any changes
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      run: |-
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        git config user.name "Automated"
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        git config user.email "actions@users.noreply.github.com"
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        git add simonwillisonblog
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        timestamp=$(date -u)
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        git commit -m "Latest data: ${timestamp}" || exit 0
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        git push

I decided to upgrade it to also build and deploy a SQLite database of the content to datasette.simonwillison.net - but only if a change had been detected.

I figured out the following pattern for doing that.

First, I added a line to the above block that set a change_detected output variable for that step if it made it past the || exit 0. I also added an id to the step so I could reference it later on:

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    - name: Commit any changes
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      id: commit_and_push
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      run: |-
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        git config user.name "Automated"
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        git config user.email "actions@users.noreply.github.com"
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        git add simonwillisonblog
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        timestamp=$(date -u)
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        git commit -m "Latest data: ${timestamp}" || exit 0
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        git push
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        echo "::set-output name=change_detected::1"

This next piece took me a while to figure out: I also had to declare that output variable at the top of the initial job, copying the result of the named step:

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jobs:
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  backup:
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    runs-on: ubuntu-latest
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    outputs:
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      change_detected: ${{ steps.commit_and_push.outputs.change_detected }}

Without this, the output is not visible to the second job.

My second job started like this:

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  build_and_deploy:
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    runs-on: ubuntu-latest
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    needs: backup
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    if: ${{ inputs.force_deploy || needs.backup.outputs.change_detected }}
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    steps:

This second job is called build_and_deploy and specify that it needs: backup - so it should run directly after that backup job completes.

That new job has an if: expression which looks at needs.backup.outputs.change_detected to read the variable that was set by my echo "::set-output line.

I’m also checking inputs.force_deploy here. That’s a separate mechanism, which allows me to trigger the workflow with manually and specify that a deploy should happen even if no changes were detected - useful for when I alter the code that configures the deployed Datasette instance.

The force_deploy variable comes from this section at the start of the YAML:

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on:
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  push:
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    branches:
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      - main
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  workflow_dispatch:
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    inputs:
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      force_deploy:
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        description: 'Deploy even if no changes detected'
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        required: false
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        type: boolean

This configuration adds the following UI which I can use to manually trigger the workflow: