0.17.4

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Argument and Input validation

Scalars

The standard way to ensure that inputs and arguments are correct, such as an email field that really contains a proper e-mail address, is to use custom scalars e.g. GraphQLEmail from graphql-custom-types. However, creating scalars for all single cases of data types (credit card number, base64, IP, URL) might be cumbersome.

That's why TypeGraphQL has built-in support for argument and input validation by using the class-validator library! We can use the awesomeness of decorators to easily declare the requirements for incoming data (e.g. a number is in the range 0-255 or a password that is longer than 8 characters).

How to use

First we decorate the input/arguments class with the appropriate decorators from class-validator. So we take this:

@InputType()
export class RecipeInput {
  @Field()
  title: string;

  @Field({ nullable: true })
  description?: string;
}

...and turn it into this:

import { MaxLength, Length } from "class-validator";

@InputType()
export class RecipeInput {
  @Field()
  @MaxLength(30)
  title: string;

  @Field({ nullable: true })
  @Length(30, 255)
  description?: string;
}

And that's it! 😉

TypeGraphQL will automatically validate our inputs and arguments based on the definitions:

@Resolver(of => Recipe)
export class RecipeResolver {
  @Mutation(returns => Recipe)
  async addRecipe(@Arg("input") recipeInput: RecipeInput): Promise<Recipe> {
    // you can be 100% sure that the input is correct
    console.assert(recipeInput.title.length <= 30);
    console.assert(recipeInput.description.length >= 30);
    console.assert(recipeInput.description.length <= 255);
  }
}

Of course, there are many more decorators we have access to, not just the simple @Length decorator used in the example above, so take a look at the class-validator documentation.

This feature is enabled by default. However, we can disable it if we must:

const schema = await buildSchema({
  resolvers: [RecipeResolver],
  validate: false, // disable automatic validation or pass the default config object
});

And we can still enable it per resolver's argument if we need to:

class RecipeResolver {
  @Mutation(returns => Recipe)
  async addRecipe(@Arg("input", { validate: true }) recipeInput: RecipeInput) {
    // ...
  }
}

The ValidatorOptions object used for setting features like validation groups can also be passed:

class RecipeResolver {
  @Mutation(returns => Recipe)
  async addRecipe(
    @Arg("input", { validate: { groups: ["admin"] } })
    recipeInput: RecipeInput,
  ) {
    // ...
  }
}

Note that by default, the skipMissingProperties setting of the class-validator is set to true because GraphQL will independently check whether the params/fields exist or not.

GraphQL will also check whether the fields have correct types (String, Int, Float, Boolean, etc.) so we don't have to use the @IsOptional, @Allow, @IsString or the @IsInt decorators at all!

Response to the Client

When a client sends incorrect data to the server:

mutation ValidationMutation {
  addRecipe(
    input: {
      # too long!
      title: "Lorem ipsum dolor sit amet, Lorem ipsum dolor sit amet"
    }
  ) {
    title
    creationDate
  }
}

the ArgumentValidationError will be thrown.

By default, the apollo-server package from the bootstrap guide will format the error to match the GraphQLFormattedError interface. So when the ArgumentValidationError occurs, the client will receive this JSON with a nice validationErrors property inside of extensions.exception:

{
  "errors": [
    {
      "message": "Argument Validation Error",
      "locations": [
        {
          "line": 2,
          "column": 3
        }
      ],
      "path": ["addRecipe"],
      "extensions": {
        "code": "INTERNAL_SERVER_ERROR",
        "exception": {
          "validationErrors": [
            {
              "target": {
                "title": "Lorem ipsum dolor sit amet, Lorem ipsum dolor sit amet"
              },
              "value": "Lorem ipsum dolor sit amet, Lorem ipsum dolor sit amet",
              "property": "title",
              "children": [],
              "constraints": {
                "maxLength": "title must be shorter than or equal to 30 characters"
              }
            }
          ],
          "stacktrace": [
            "Error: Argument Validation Error",
            "    at Object.<anonymous> (F:\\#Projekty\\type-graphql\\src\\resolvers\\validate-arg.ts:29:11)",
            "    at Generator.throw (<anonymous>)",
            "    at rejected (F:\\#Projekty\\type-graphql\\node_modules\\tslib\\tslib.js:105:69)",
            "    at processTicksAndRejections (internal/process/next_tick.js:81:5)"
          ]
        }
      }
    }
  ],
  "data": null
}

Of course we can also create our own custom implementation of the formatError function provided in the ApolloServer config options which will transform the GraphQLError with a ValidationError array in the desired output format (e.g. extensions.code = "ARGUMENT_VALIDATION_ERROR").

Example

To see how this works, check out the simple real life example.

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