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Version: 0.17

Schema Evolution

Schema evolution lets different versions of your service exchange messages safely — a v2 writer can produce a message a v1 reader still understands, and vice versa.

Two Modes​

  • Schema-consistent mode (default): more compact, but both sides must have exactly the same schema. Good when all services update together.
  • Compatible mode: writes extra field metadata so readers can skip unknown fields and tolerate missing ones. Good for independent deployments or rolling upgrades.

Enable Compatible Mode​

const fory = new Fory({ compatible: true });

Use this when:

  • services deploy schema changes independently
  • older readers may see newer payloads
  • newer readers may see older payloads from before a field was added

Example​

Writer schema:

const writerType = Type.struct(
  { typeId: 1001 },
  {
    name: Type.string(),
    age: Type.int32(),
  },
);

Reader schema with fewer fields:

const readerType = Type.struct(
  { typeId: 1001 },
  {
    name: Type.string(),
  },
);

With compatible: true, the reader ignores fields it does not know about, and fills unknown fields with default values.

Opting Out of Evolution for One Struct​

You can disable evolution metadata for a specific struct even inside a compatible: true instance:

const fixedType = Type.struct(
  { typeId: 1002, evolving: false },
  {
    name: Type.string(),
  },
);

evolving: false produces smaller messages for that struct, but both the writer and reader must agree on this setting. If one side writes with evolving: false and the other reads expecting compatible metadata, deserialization will fail.

When to Use Each Mode​

Schema-consistentCompatible
Services always update together✔ best choiceworks, but wasteful
Independent deploymentswill break✔ best choice
Smallest possible messages✔slightly larger
Rolling upgradesrisky✔ safe

Cross-Language Requirement​

Compatible mode only protects you from schema differences in the fields of a type. You still need the same type identity (same numeric ID or same namespace + typeName) on every side. See Cross-Language.