documents different approach for initial population of data #6691
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| In many cases, an app may wish to make use of Nautobot's various extensibility features, such as [custom fields](../../../../user-guide/platform-functionality/customfield.md) or [relationships](../../../../user-guide/platform-functionality/relationship.md). It can be useful for an app to automatically create a custom field definition or relationship definition as a consequence of being installed and activated, so that everyday usage of the app can rely upon these definitions to be present. | ||
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| To make this possible, Nautobot provides a custom [signal](https://docs.djangoproject.com/en/stable/topics/signals/), `nautobot_database_ready`, that apps can register to listen for. This signal is triggered when `nautobot-server migrate` or `nautobot-server post_upgrade` is run after installing an app, and provides an opportunity for the app to make any desired additions to the database at this time. | ||
| Furthermore, sometimes apps might want to create a baseline of available data. This could, for example, be a baseline of circuit providers for an SSoT app that synchronizes circuit data. |
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May want to define SSoT here as it's the first time it's referenced in the doc?
A couple other examples would probably be helpful to get developers thinking; the one I've seen the most is creating default Status and/or Role records (or just adding to the content_types of existing records) to use with an app's new data models.
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| **Con**: | ||
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| - Prevent Nautobot from starting when there are errors |
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- Re-runs every time
nautobot-server migrateornautobot-server post_upgradeis run- Must be idempotent (doesn't introduce duplicate records or error out if run repeatedly)
- May recreate or revert records that a user intentionally deleted or altered
- Nautobot startup/upgrade performance?
- The possibility of later user modifications to data must be accounted for and handled in code.
| **Pro**: | ||
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| - Execution: Automatic | ||
| - Provide a clean way to delete any associated objects when uninstalling the app |
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- Runs exactly once (on
nautobot-server migrateornautobot-server post_upgrade), so idempotence is not a concern, and will not later revert or recreate records that a user intentionally deleted or altered. - Users can later modify the created data like any other record, if a need arises.
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| - Implementation: Medium | ||
| - Prevent Nautobot from starting when there are errors | ||
| - Immutable—if you add new objects, you need to add a new migration |
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Suggested change
| - Immutable—if you add new objects, you need to add a new migration | |
| - Immutable — if you later need to add new objects or alter existing one, you need to add a new migration |
| **Pro**: | ||
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| - Execution: Automatic | ||
| - Implementation: Easy |
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- Can be rerun as needed (opposite of "Con" on data migrations below)
- Can be updated "in place" in later App releases (opposite of "Con" on data migrations below)
- Users can later modify the created data like any other record, if a need arises.
| **Con**: | ||
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| - Data is not available in the DB/API/GUI until the process that uses it runs | ||
| - Some care has to be taken to not duplicate information if multiple things depend on this data |
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- Later modifications to the object definitions may be error-prone if a given record/set of attributes is created/referenced in many locations
- User modifications to the data may result in side effects (renaming a Status may result in a new Status with the original name being recreated next time the code runs, etc.)
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| - Execution: Manual | ||
| - Implementation: Medium | ||
| - Creating/updating them is not straight-forward, especially for big data sets |
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- The possibility of later user modifications to data must be accounted for and handled in code.
| **Pro**: | ||
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| - Have good support for usage in unit tests | ||
| - Have good performance |
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- Users can later modify the created data like any other record, if a need arises.
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| **Con**: | ||
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| - Execution: Manual |
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- The possibility of later user modifications to data must be accounted for and handled in code.
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| - Signal Handlers on `nautobot_database_ready` (see above) | ||
| - [Django Onboard Tooling](https://docs.djangoproject.com/en/4.2/howto/initial-data/) | ||
| - [Django Data Migrations](https://docs.djangoproject.com/en/4.2/topics/migrations/#data-migrations) | ||
| - [Django Fixtures](https://docs.djangoproject.com/en/4.2/topics/db/fixtures/#fixtures) | ||
| - [Design Builder Jobs](https://docs.nautobot.com/projects/design-builder/en/latest/) | ||
| - Creating data in-place where needed |
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Given the repetition of pros/cons below, I wonder if it'd be possible and reasonable to create a table here of approaches versus their use cases/pros/cons?
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Closes #6671
What's Changed
See attached issue.
TODO