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Validation ​

Custom scalars can be useful for handling specific data types that are not natively supported by GraphQL or you want a version of an existing type that does some validation.

In this example, we create a new scalar type Username, which ensures that the username is longer than 3 characters. In case of success the request proceeds, otherwise an error is thrown.

ts
import { g, InferResolvers, buildSchema } from 'garph'
import { GraphQLError } from 'graphql'

const username = g.scalarType<string, string>('Username', {
  serialize: (username) => username,
  parseValue: (username) => {
    if (username.length < 3) {
      throw new GraphQLError('Username must be at least 3 characters long')
    }

    return username
  }
})

const queryType = g.type('Query', {
  login: g.string().args({ username }),
})

const resolvers: InferResolvers<{ Query: typeof queryType }, {}> = {
  Query: {
    login: (parent, args) => `Welcome back, ${args.username}!`
  }
}

const schema = buildSchema({ g, resolvers })
import { g, InferResolvers, buildSchema } from 'garph'
import { GraphQLError } from 'graphql'

const username = g.scalarType<string, string>('Username', {
  serialize: (username) => username,
  parseValue: (username) => {
    if (username.length < 3) {
      throw new GraphQLError('Username must be at least 3 characters long')
    }

    return username
  }
})

const queryType = g.type('Query', {
  login: g.string().args({ username }),
})

const resolvers: InferResolvers<{ Query: typeof queryType }, {}> = {
  Query: {
    login: (parent, args) => `Welcome back, ${args.username}!`
  }
}

const schema = buildSchema({ g, resolvers })

Validating with Zod ​

Same as the example above, except we are now using Zod validator instead of writing the logic ourselves.

Before you continue, make sure you have installed Zod from NPM

ts
import { g, InferResolvers, buildSchema } from 'garph'
import { z } from 'zod'
import { GraphQLError } from 'graphql'

const usernameValidator = z.string().min(3)

const username = g.scalarType<string, string>('Username', {
  serialize: (username) => username,
  parseValue: (username) => {
    if (!usernameValidator.safeParse(username).success) {
      throw new GraphQLError('Username must be at least 3 characters long')
    }

    return username
  }
})

const queryType = g.type('Query', {
  login: g.string().args({ username }),
})

const resolvers: InferResolvers<{ Query: typeof queryType }, {}> = {
  Query: {
    login: (parent, args) => `Welcome back, ${args.username}!`
  }
}

const schema = buildSchema({ g, resolvers })
import { g, InferResolvers, buildSchema } from 'garph'
import { z } from 'zod'
import { GraphQLError } from 'graphql'

const usernameValidator = z.string().min(3)

const username = g.scalarType<string, string>('Username', {
  serialize: (username) => username,
  parseValue: (username) => {
    if (!usernameValidator.safeParse(username).success) {
      throw new GraphQLError('Username must be at least 3 characters long')
    }

    return username
  }
})

const queryType = g.type('Query', {
  login: g.string().args({ username }),
})

const resolvers: InferResolvers<{ Query: typeof queryType }, {}> = {
  Query: {
    login: (parent, args) => `Welcome back, ${args.username}!`
  }
}

const schema = buildSchema({ g, resolvers })