Checkpointing

This section is largely a light introduction to the hof datamodel command, or hof dm for short.

As we have mentioned, the hof dm subcommands are utilities for managing the versioning and history of your datamodels.

Available Commands:
  checkpoint  create a snapshot of the data model
  diff        show the diff between data model version
  history     list the snapshots for a data model
  info        print details for a data model
  list        print available data models
  log         show the history of diffs for a data model

Run hof dm -h for the full listing. The top-level data-modeling goes deeper into the command and many related topics.

Checkpointing

We can run hof dm checkpoint to create a versioned snapshot of our data model. With many snapshots, we can introspect the history and diff between versions. This opens up some interesting possibilities:

• check backwards compatibility and suggest appropriate semantic version changes
• automatically generating migrations as our program and data model evolve
• generating transformation functions between versions
  • for supporting many versions while keeping business logic clear of these details
    • feature flag capabilities
    • deploying migrations and applications updates without downtime or coordination

The inspiration for some of this is

• automating database migrations as applications evolve
• Project Cambria for the lenses concept
• grafana/thema for lacuna, or filling the gaps

Trying hof dm

You can try out the hof dm commands by

1. hof dm checkpoint to create a first snapshot
2. hof dm ... list, info, history to introspect
3. add some fields or new models
4. hof dm diff to see what has changed
5. the introspection commands to see backwards compatibility