{
  "title": "Schema Evolution - Backward Compatible Change",
  "description": "Example of a backward compatible schema change: adding an optional field with a default value to an existing Avro schema. The new schema can read data written with the old schema.",
  "schemaV1": {
    "type": "record",
    "name": "OrderEvent",
    "namespace": "com.example.events",
    "fields": [
      { "name": "orderId", "type": "string" },
      { "name": "customerId", "type": "string" },
      { "name": "totalAmount", "type": "double" },
      { "name": "status", "type": { "type": "enum", "name": "OrderStatus", "symbols": ["PENDING", "PROCESSING", "SHIPPED", "DELIVERED", "CANCELLED"] } },
      { "name": "createdAt", "type": "string" }
    ]
  },
  "schemaV2": {
    "type": "record",
    "name": "OrderEvent",
    "namespace": "com.example.events",
    "fields": [
      { "name": "orderId", "type": "string" },
      { "name": "customerId", "type": "string" },
      { "name": "totalAmount", "type": "double" },
      { "name": "status", "type": { "type": "enum", "name": "OrderStatus", "symbols": ["PENDING", "PROCESSING", "SHIPPED", "DELIVERED", "CANCELLED"] } },
      { "name": "createdAt", "type": "string" },
      {
        "name": "shippingMethod",
        "type": ["null", "string"],
        "default": null,
        "doc": "Shipping carrier and service level. Added in v2."
      },
      {
        "name": "currency",
        "type": "string",
        "default": "USD",
        "doc": "ISO 4217 currency code. Added in v2 with backward-compatible default."
      }
    ]
  },
  "changeRecord": {
    "schemaName": "OrderEvent",
    "fromVersion": "1.0.0",
    "toVersion": "2.0.0",
    "changes": [
      {
        "changeType": "field-added",
        "fieldPath": "fields.shippingMethod",
        "compatibilityImpact": "backward-compatible",
        "description": "Added optional shippingMethod field with null default. Old messages that lack this field will deserialize with null value."
      },
      {
        "changeType": "field-added",
        "fieldPath": "fields.currency",
        "compatibilityImpact": "backward-compatible",
        "description": "Added currency field with default 'USD'. Old messages without this field will be read as USD."
      }
    ],
    "migrationRequired": false
  }
}