Effect CommunityEC
Effect Community•2y ago•
2 replies
whatplan

Handling Conditional Defaults in API Schema Parsing

I am parsing a schema for an api endpoint it has some optional options with defaults
however, there is one specific scenario where based on a condition I determine sometime after parsing I need to know whether a value was provided or from the default

basically if the condition is true I first need to check if foo was provided in the body, if not then look at another optional thing, and then finally use the default value of the schema

import * as S from "@effect/schema/Schema";

const Body = S.Struct({
  foo: S.String.pipe(S.optional({ default: () => "foo" })),
});

declare const bodyJson: unknown;

const result = S.decodeUnknownSync(Body)(bodyJson);

// use result.foo in a couple places where the default value is expected if the value was not provided

declare const otherThing: { foo: string | undefined };
declare const condition: boolean;

const finalValue = (() => {
  if (
    condition &&
    typeof bodyJson === "object" &&
    bodyJson !== null &&
    "foo" in bodyJson &&
    typeof bodyJson.foo === "string"
  ) {
    return bodyJson.foo;
  } else if (otherThing.foo) {
    return otherThing.foo;
  } else {
    return result.foo;
  }
})();


the solutions I have thought of are:
1. use S.optionalToRequired and map the 
T | undefined
 to { value: T, provided: boolean }
2. create a schema that requires some services that inject the otherThing and the condition and inject them and use the result of that special schema in this specific scenario

thoughts appriciated
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