How do you implement and use a custom GraphQL scalar type in NestJS?

Q: How do you implement and use a custom GraphQL scalar type in NestJS?

import { Scalar, CustomScalar } from '@nestjs/graphql'; import { Kind, ValueNode } from 'graphql'; @Scalar('Date', () => Date) export class DateScalarProvider implements CustomScalar { description = 'Date custom scalar — ISO-8601 string'; // server -> client: Date object to ISO string serialize(value: Date): string { return value.toISOString(); } // client -> server (variable): string to Date parseValue(value: string): Date { return new Date(value); } // client -> server (inline literal in query): string literal to Date parseLiteral(ast: ValueNode): Date | null { if (ast.kind === Kind.STRING) return new Date(ast.value); return null; } } // Register in module @Module({ providers: [DateScalarProvider, UsersResolver], }) export class UsersModule {} // Use in object types @ObjectType() export class User { @Field(() => Date) createdAt: Date; @Field(() => Date) updatedAt: Date; } serialize() — converts the server-side value to the wire format sent to the client. parseValue() — converts a client-provided variable value to the server-side type. parseLiteral() — converts an inline literal in the query document to the server-side type. The scalar name in @Scalar() must match the name used in @Field(() => ScalarType). Add the scalar class to the module providers — it is not auto-discovered.

Difficulty: 5/10

custom scalar implementation, validation & parsing, NestJS GraphQL integration

Implement the scalar as a class decorated with @Scalar('ScalarName', () => NativeType) and add it to the module's providers array. The class must define parseValue (client to server), serialize (server to client), and parseLiteral (inline literal in the query). The scalar name in @Scalar() must match the @Field() type annotation.

Custom Date scalar implementation

Custom scalar implementation rules:

1
serialize() — converts the server-side value to the wire format sent to the client.
2

How do you implement and use a custom GraphQL scalar type in NestJS?

Difficulty: 5/10

custom scalar implementation, validation & parsing, NestJS GraphQL integration

Implement the scalar as a class decorated with @Scalar('ScalarName', () => NativeType) and add it to the module's providers array. The class must define parseValue (client to server), serialize (server to client), and parseLiteral (inline literal in the query). The scalar name in @Scalar() must match the @Field() type annotation.

Custom Date scalar implementation

Custom scalar implementation rules:

1
serialize() — converts the server-side value to the wire format sent to the client.
2

How do you implement and use a custom GraphQL scalar type in NestJS?

How do you implement and use a custom GraphQL scalar type in NestJS?

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