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Nexus Client Code Generator

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caution

nexgen is pre-release software and may not retain backwards compatibility with previous versions of the tool. It is not yet published to any package registry, so you build it from source.

A Nexus Service is a contract meant to be shared across team boundaries. Those teams often work in different languages, so the same request and response types get hand-written for each SDK. Hand-written copies drift: a field is required on one side and optional on the other, a bound is enforced by the caller but not the handler.

The Nexus Client Code Generator removes those copies. You describe your types and Nexus Operations once in a definition file, and the generator emits the equivalent library code for Go, Java, Python, and TypeScript. The generator is a command-line tool named nexgen, distributed from the temporalio/nexgen repository.

What the generator produces​

The generator produces a client library for the inputs and outputs of your Nexus Operations. The generated types check values against the contract as they are sent and received, so a violation surfaces as an error rather than as bad data.

That client library contains three things:

  • A typed model. An idiomatic struct, class, interface, or dataclass, with doc comments carried over from the schema.
  • A runtime validator. One validator per type, applied when a value is parsed off the wire and again when it is serialized onto it.
  • A Nexus Service Contract definition, for a file that declares Services. These are the Service and Operation declarations you register on a Worker and call from a caller Workflow. A pure JSON Schema file declares none, so it produces only the models and their validators.

Constraint failures are aggregated into a single native error listing every violation, each naming the offending field and the bound it broke. A handler maps that error to a BAD_REQUEST Nexus error, so a malformed request tells the caller everything that was wrong with it in one response.