Allows using @constraint as a directive to validate input data. Inspired by Constraints Directives RFC and OpenAPI

npm install graphql-constraint-directive 

const ConstraintDirective = require('graphql-constraint-directive') const express = require('express') const bodyParser = require('body-parser') const { graphqlExpress } = require('apollo-server-express') const { makeExecutableSchema } = require('graphql-tools') const typeDefs = `  type Query {  books: [Book]  }  type Book {  title: String  }  type Mutation {  createBook(input: BookInput): Book  }  input BookInput {  title: String! @constraint(minLength: 5, format: "email")  }` const schema = makeExecutableSchema({ typeDefs, schemaDirectives: { constraint: ConstraintDirective } }) const app = express() app.use('/graphql', bodyParser.json(), graphqlExpress({ schema }))

@constraint(minLength: 5) Restrict to a minimum length

@constraint(maxLength: 5) Restrict to a maximum length

@constraint(startsWith: "foo") Ensure value starts with foo

@constraint(endsWith: "foo") Ensure value ends with foo

@constraint(contains: "foo") Ensure value contains foo

@constraint(notContains: "foo") Ensure value does not contain foo

@constraint(pattern: "^[0-9a-zA-Z]*$") Ensure value matches regex, e.g. alphanumeric

@constraint(format: "email") Ensure value is in a particular format

Supported formats:

• byte: Base64
• date-time: RFC 3339
• date: ISO 8601
• email
• ipv4
• ipv6
• uri
• uuid

@constraint(min: 3) Ensure value is greater than or equal to

@constraint(max: 3) Ensure value is less than or equal to

@constraint(exclusiveMin: 3) Ensure value is greater than

@constraint(exclusiveMax: 3) Ensure value is less than

@constraint(multipleOf: 10) Ensure value is a multiple

Each validation error throws a ConstraintDirectiveError. Combined with a formatError function, this can be used to customise error messages.

{ code: 'ERR_GRAPHQL_CONSTRAINT_VALIDATION', fieldName: 'theFieldName', context: [ { arg: 'argument name which failed', value: 'value of argument' } ] }

const formatError = function (error) { if (error.originalError && error.originalError.code === 'ERR_GRAPHQL_CONSTRAINT_VALIDATION') { // return a custom object } return error } app.use('/graphql', bodyParser.json(), graphqlExpress({ schema, formatError }))