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Add additional details about dropping columns to 50-50 state documentation #538

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Apr 17, 2024
Merged

Add additional details about dropping columns to 50-50 state documentation #538

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Add additional details about dropping columns to 50-50 state document…
zachmargolis Apr 16, 2024
062c488
Add a little more explanation
zachmargolis Apr 16, 2024
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14 changes: 14 additions & 0 deletions _articles/manage-50-50-state.md
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Expand Up @@ -33,8 +33,22 @@ existing data.

### Remove a table or field
* Deploy 1: Remove all reads in the code
* If removing a field from an in-use table, mark that field as an ignored columns.
This is necessary in the IDP because it is [configured to explicitly load columns][idp-explicit-config]
instead of using `SELECT *`.

```ruby
class MyTable < ApplicationRecord
self.ignored_columns = %w[my_column_to_drop]
end
```

* Deploy 2: Remove all writes in the code
* Deploy 3: Remove the table/field
* If removing a field, the field can be removed from the ignored columns list
* If removing a table, the entire model file can be removed

[idp-explicit-config]: https://github.com/18F/identity-idp/blob/c4a0cc098867a209f8196c312024b24001b6fa9b/app/models/application_record.rb#L6-L7

## Persistent data structures in redis

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