Schema Projections

Sometimes, you may want to create a new schema based on an existing one, focusing specifically on either its Type or Encoded aspect. The Schema module provides several functions to make this possible.

toType

Schema.toType extracts the decoded side of a schema. The result has the original Type as both its Type and Encoded, requires no services, and discards the encoding path.

Function Signature

declare const toType: <S extends Schema.Constraint>(
  schema: S,
) => Schema.toType<S>

Example (Extracting Only Type-Specific Properties)

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import { Schema } from "effect"
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const Original = Schema.Struct({
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  quantity: Schema.FiniteFromString.check(Schema.isGreaterThanOrEqualTo(2)),
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})
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// This creates a schema where 'quantity' is defined as a number
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// that must be greater than or equal to 2.
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const TypeSchema = Schema.toType(Original)
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// TypeSchema is equivalent to:
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const TypeSchema2 = Schema.Struct({
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  quantity: Schema.Finite.check(Schema.isGreaterThanOrEqualTo(2)),
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})
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Schema.decodeUnknownSync(TypeSchema)({ quantity: 5 }) // => { quantity: 5 }

toEncoded

Schema.toEncoded extracts the encoded side of a schema. The result has the original Encoded as both its Type and Encoded, requires no services, and discards the decoding path while preserving checks that apply to the encoded representation.

Function Signature

declare const toEncoded: <S extends Schema.Constraint>(
  schema: S,
) => Schema.toEncoded<S>

Example (Retaining Initial Refinements Only)

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import { Schema } from "effect"
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const Original = Schema.Struct({
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  foo: Schema.String.check(Schema.isMinLength(3)).pipe(
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    Schema.decodeTo(Schema.Trim),
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  ),
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})
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// The EncodedSchema preserves the minLength(3) check,
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// ensuring the string length condition is enforced
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// but omits the Schema.Trim transformation.
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const EncodedSchema = Schema.toEncoded(Original)
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// EncodedSchema is equivalent to:
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const EncodedSchema2 = Schema.Struct({
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  foo: Schema.String.check(Schema.isMinLength(3)),
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})
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Schema.decodeUnknownSync(EncodedSchema)({ foo: "abcd" }) // => { foo: "abcd" }