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title Schema Evolution
sidebar_position 60
id schema_evolution
license Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to You under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

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.

Compatible Mode

Compatible mode is the default. It writes extra field metadata so readers can skip unknown fields and tolerate missing ones. Keep it for independent deployments, rolling upgrades, and xlang services. For payloads whose reader and writer schemas never differ, see When to Use Each Mode.

Compatible readers also tolerate selected scalar field type changes when the conversion is lossless. A matched field can read between boolean, string, numeric scalars, and Decimal when the converted value has the same logical value. For example, "true", "false", "1", and "0" can be read as booleans, exact finite ASCII numeric strings can be read as numeric fields that can hold them, numbers and decimals can be read as canonical strings, and numeric widening or narrowing succeeds only when no precision or range is lost. Invalid strings and lossy conversions fail during deserialization. Nullable fields still compose with these conversions, but reference-tracked scalar type changes are incompatible.

Default Compatible Mode

const fory = new Fory();

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 mode, the reader ignores fields it does not know about, and fills unknown fields with default values.

When to Use Each Mode

Requirement Same-schema opt-out Compatible mode
Every reader and writer uses the same schema works works
Independent deployments unsafe recommended
Best size and speed for same-schema data yes no
Rolling upgrades unsafe recommended

Set compatible: false for xlang payloads only after verifying that every language uses the same schema, or when native types are generated from Fory schema IDL.

Same-Schema Per-Struct Opt-Out

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 can be faster and smaller for that struct. Use it only when every reader and writer always uses the same struct schema. If one side writes with evolving: false and the other reads expecting compatible metadata, deserialization will fail.

Xlang 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 typeName) on every side. See Xlang Serialization.

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