Merge pull request #24 from microbiomedata/eecavanna-decisions-0007-m…

…ongo-migration-scripts

ADR: Document decision to provide data migration scripts alongside schema changes

decisions/0007-mongo-migration-scripts.md

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+---
+status: accepted
+date: 2023-08-01
+deciders: @eecavanna, @Shalsh23, @shreddd, @turbomam, @dwinston
+consulted: (same as `deciders`)
+informed: All existing `nmdc-schema` and `nmdc-runtime` contributors
+---
+# Mongo schema changes will always be accompanied by data migration scripts
+
+## Context and Problem Statement
+
+The Mongo database used by the NMDC contains data that adheres to the specific version of `nmdc-schema` being imported by `nmdc-runtime`. Over time, new versions of `nmdc-schema` are imported into `nmdc-runtime`.
+
+Currently, when a new version of `nmdc-schema` is imported into `nmdc-runtime`, the maintainers of `nmdc-runtime` do not always know whether any changes to existing data will be required in order to make it so that the existing data adheres to the new version of `nmdc-schema`; and, if so, what those changes are.
+
+## Considered Options
+
+1. An `nmdc-schema` maintainer and an `nmdc-runtime` maintainer discuss each new version of `nmdc-schema` before it gets imported into `nmdc-runtime`
+2. An `nmdc-schema` maintainer commits a data migration script (which may be a no-op) in the `nmdc-schema` repository along with each unit of schema changes
+
+## Decision Outcome
+
+Chosen option: "An `nmdc-schema` maintainer commits a data migration script (which may be a no-op) in the `nmdc-schema` repository along with each unit of schema changes"
+
+This was chosen because it will make it so the data changes (or lack thereof) are explicitly documented, in a standard format and location, and can (eventually) be performed by a CI system.