{
  "id": "database-migration-rehearsal",
  "title": "Database Migration Rehearsal",
  "level": 3,
  "languages": [
    "Python"
  ],
  "source": "core",
  "tagline": "Rehearse a proposed migration on a copy and show exactly what changes.",
  "summary": "Let a developer or coding agent propose SQLite migrations against a disposable database copy. Record schema and row-count invariants before and after, test declared rollback steps, and expose irreversible changes. Export a machine-readable rehearsal receipt and review page without touching the source database.",
  "prerequisiteProjects": [
    "csv-sql-question-workbench",
    "json-schema-output-guard"
  ],
  "status": "ready",
  "hours": 8,
  "prerequisites": [
    "Python 3.10+; lists, dictionaries and functions"
  ],
  "skills": [
    "Snapshot a local database and define invariants",
    "Apply migrations only to the disposable copy",
    "Exercise rollback and detect data loss",
    "Export evidence for an explicit release decision"
  ],
  "youWillBuild": "Schema diff, invariant results and reversible-migration receipt",
  "author": {
    "name": "AI Engineering from Scratch",
    "github": "rohitg00"
  },
  "overviewFigure": "pj-database-migration-rehearsal-1",
  "figures": true,
  "demo": {
    "cwd": "solution",
    "command": [
      "python3",
      "cli.py",
      "samples/input.json",
      "--output",
      "demo-output"
    ]
  },
  "stages": [
    {
      "id": "01-snapshot",
      "title": "Snapshot a local database and define invariants",
      "summary": "Capture schema, row counts and content identities from a read-only source.",
      "hours": 2,
      "language": "python",
      "difficulty": "starter",
      "concepts": [
        "SQLite backup",
        "row fingerprints"
      ],
      "figure": "pj-database-migration-rehearsal-1"
    },
    {
      "id": "02-migration",
      "title": "Apply migrations only to the disposable copy",
      "summary": "Run the supplied SQL on a disposable in-memory copy.",
      "hours": 2,
      "language": "python",
      "difficulty": "core",
      "concepts": [
        "SQLite authorizer",
        "migration evidence"
      ],
      "figure": "pj-database-migration-rehearsal-2"
    },
    {
      "id": "03-rollback",
      "title": "Exercise rollback and detect data loss",
      "summary": "Exercise the declared reverse operation and compare all captured state.",
      "hours": 2,
      "language": "python",
      "difficulty": "core",
      "concepts": [
        "rollback verification",
        "data loss"
      ],
      "figure": "pj-database-migration-rehearsal-3"
    },
    {
      "id": "04-receipt",
      "title": "Export evidence for an explicit release decision",
      "summary": "Combine schema diffs, invariants and rollback into release evidence.",
      "hours": 2,
      "language": "python",
      "difficulty": "core",
      "concepts": [
        "invariants",
        "release review"
      ],
      "figure": "pj-database-migration-rehearsal-4"
    }
  ],
  "demos": [
    {
      "gif": "media/run.gif",
      "poster": "media/run.png",
      "title": "Initialize and grade",
      "caption": "Recorded starter failure followed by every reference stage passing."
    },
    {
      "gif": "media/output.gif",
      "poster": "media/output.png",
      "title": "Inspect actual output",
      "caption": "Recorded interaction with the generated local interface. Run the documented command to inspect your own output."
    }
  ]
}