Adding new columns to a snapshot

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1

I have the following snapshot:

{% snapshot meter_readings_snapshot %}

    {{
        config(
          target_schema=get_snapshot_schema(),
          unique_key='id',

          strategy='timestamp_with_nulls',
          updated_at='updated_at',
          invalidate_hard_deletes=True,
        )
    }}

select id,
       meter_id,
       estar_meter_reading_id,
       from_date,
       to_date,
       cost,
       usage,
       exported,
       demand,
       demand_charge,
       is_custom,
       created_at,
       is_estimate,
       updated_at,
       _sdc_extracted_at,
       _sdc_batched_at,
       _sdc_deleted_at

from {{ source('CORE', 'METER_READINGS') }}

{% endsnapshot %}

We added two new columns to this METER_READINGS table in Production (updated_by and created_by), but now I would like to add those columns to the snapshot. I expected that the next time dbt ran it would pull in those new columns, pull in the current values for the columns, and then all the historical data where dbt_valid_to is not null would have null values for the new fields. That’s not what happened. Instead I got two new columns that were almost entirely null, and then I’m slowly getting values, presumably as people make changes, again presumably because of the update strategy, I imagine?

So… my question is, how do I need to go about this so that I preserve all the historical data we’ve been collecting for years, while also bringing in the current values of the two new columns for all the current rows? Thanks all.