Errors plugin

A plugin for easily including error types in your GraphQL schema and hooking up error types to resolvers

Usage

Install

npm install --save @pothos/plugin-errors

Setup

Ensure that the target in your tsconfig.json is set to es6 or higher (default is es3).

Example Usage

import ErrorsPlugin from '@pothos/plugin-errors';
const builder = new SchemaBuilder({
  plugins: [ErrorsPlugin],
  errors: {
    defaultTypes: [],
  },
});
 
builder.objectType(Error, {
  name: 'Error',
  fields: (t) => ({
    message: t.exposeString('message'),
  }),
});
 
builder.queryType({
  fields: (t) => ({
    hello: t.string({
      errors: {
        types: [Error],
      },
      args: {
        name: t.arg.string({ required: false }),
      },
      resolve: (parent, { name }) => {
        if (name.slice(0, 1) !== name.slice(0, 1).toUpperCase()) {
          throw new Error('name must be capitalized');
        }
 
        return `hello, ${name || 'World'}`;
      },
    }),
  }),
});

The above example will produce a GraphQL schema that looks like:

type Error {
  message: String!
}
 
type Query {
  hello(name: String!): QueryHelloResult
}
 
union QueryHelloResult = Error | QueryHelloSuccess
 
type QueryHelloSuccess {
  data: String!
}

This field can be queried using fragments like:

query {
  hello(name: "World") {
    __typename
    ... on Error {
      message
    }
    ... on QueryHelloSuccess {
      data
    }
  }
}

This plugin works by wrapping fields that define error options in a union type. This union consists of an object type for each error type defined for the field, and a Success object type that wraps the returned data. If the fields resolver throws an instance of one of the defined errors, the errors plugin will automatically resolve to the corresponding error object type.

Builder options

defaultTypes: An array of Error classes to include in every field with error handling.
directResult: Sets the default for directResult option on fields (only affects non-list fields)

defaultResultOptions: Sets the defaults for result option on fields.

name: Function to generate a custom name on the generated result types.

export const builderWithCustomErrorTypeNames = new SchemaBuilder<{}>({
  plugins: [ErrorPlugin, ValidationPlugin],
  errors: {
    defaultTypes: [Error],
    defaultResultOptions: {
      name: ({ parentTypeName, fieldName }) => `${fieldName}_Custom`,
    },
    defaultUnionOptions: {
      name: ({ parentTypeName, fieldName }) => `${fieldName}_Custom`,
    },
  },
});

defaultUnionOptions: Sets the defaults for result option on fields.

name: Function to generate a custom name on the generated union types.

export const builderWithCustomErrorTypeNames = new SchemaBuilder<{}>({
  plugins: [ErrorPlugin, ValidationPlugin],
  errors: {
    defaultTypes: [Error],
    defaultResultOptions: {
      name: ({ parentTypeName, fieldName }) => `${fieldName}_Custom`,
    },
    defaultUnionOptions: {
      name: ({ parentTypeName, fieldName }) => `${fieldName}_Custom`,
    },
  },
});

Options on Fields

types: An array of Error classes to catch and handle as error objects in the schema. Will be merged with defaultTypes from builder.
union: An options object for the union type. Can include any normal union type options, and name option for setting a custom name for the union type.
result: An options object for result object type. Can include any normal object type options, and name option for setting a custom name for the result type.
dataField: An options object for the data field on the result object. This field will be named data by default, but can be written by passsing a custom name option.
directResult: Boolean, can only be set to true for non-list fields. This will directly include the fields type in the union rather than creating an intermediate Result object type. This will throw at build time if the type is not an object type.

Recommended Usage

Set up an Error interface
Create a BaseError object type
Include the Error interface in any custom Error types you define
Include the BaseError type in the defaultTypes in the builder config

This pattern will allow you to consistently query your schema using a ... on Error { message } fragment since all Error classes extend that interface. If your client want's to query details of more specialized error types, they can just add a fragment for the errors it cares about. This pattern should also make it easier to make future changes without unexpected breaking changes for your clients.

The follow is a small example of this pattern:

import ErrorsPlugin from '@pothos/plugin-errors';
const builder = new SchemaBuilder({
  plugins: [ErrorsPlugin],
  errors: {
    defaultTypes: [Error],
  },
});
 
const ErrorInterface = builder.interfaceRef<Error>('Error').implement({
  fields: (t) => ({
    message: t.exposeString('message'),
  }),
});
 
builder.objectType(Error, {
  name: 'BaseError',
  interfaces: [ErrorInterface],
});
 
class LengthError extends Error {
  minLength: number;
 
  constructor(minLength: number) {
    super(`string length should be at least ${minLength}`);
 
    this.minLength = minLength;
    this.name = 'LengthError';
  }
}
 
builder.objectType(LengthError, {
  name: 'LengthError',
  interfaces: [ErrorInterface],
  fields: (t) => ({
    minLength: t.exposeInt('minLength'),
  }),
});
 
builder.queryType({
  fields: (t) => ({
    // Simple error handling just using base error class
    hello: t.string({
      errors: {},
      args: {
        name: t.arg.string({ required: true }),
      },
      resolve: (parent, { name }) => {
        if (!name.startsWith(name.slice(0, 1).toUpperCase())) {
          throw new Error('name must be capitalized');
        }
 
        return `hello, ${name || 'World'}`;
      },
    }),
    // Handling custom errors
    helloWithMinLength: t.string({
      errors: {
        types: [LengthError],
      },
      args: {
        name: t.arg.string({ required: true }),
      },
      resolve: (parent, { name }) => {
        if (name.length < 5) {
          throw new LengthError(5);
        }
 
        return `hello, ${name || 'World'}`;
      },
    }),
  }),
});

With validation plugin

To use this in combination with the validation plugin, ensure that that errors plugin is listed BEFORE the validation plugin in your plugin list.

Once your plugins are set up, you can define types for a ZodError, the same way you would for any other error type. Below is a simple example of how this can be done, but the specifics of how you structure your error types are left up to you.

// Util for flattening zod errors into something easier to represent in your Schema.
function flattenErrors(
  error: ZodFormattedError<unknown>,
  path: string[],
): { path: string[]; message: string }[] {
    const errors = error._errors.map((message) => ({
    path,
    message,
  }));
 
  Object.keys(error).forEach((key) => {
    if (key !== '_errors') {
      errors.push(
        ...flattenErrors((error as Record<string, unknown>)[key] as ZodFormattedError<unknown>, [
          ...path,
          key,
        ]),
      );
    }
  });
 
  return errors;
}
 
// A type for the individual validation issues
const ZodFieldError = builder
  .objectRef<{
    message: string;
    path: string[];
  }>('ZodFieldError')
  .implement({
    fields: (t) => ({
      message: t.exposeString('message'),
      path: t.exposeStringList('path'),
    }),
  });
 
// The actual error type
builder.objectType(ZodError, {
  name: 'ZodError',
  interfaces: [ErrorInterface],
  fields: (t) => ({
    fieldErrors: t.field({
      type: [ZodFieldError],
      resolve: (err) => flattenErrors(err.format(), []),
    }),
  }),
});
 
builder.queryField('fieldWIthValidation', (t) =>
  t.boolean({
    errors: {
      types: [ZodError],
    },
    args: {
      string: t.arg.string({
        validate: {
          type: 'string',
          minLength: 3,
        },
      }),
    },
    resolve: () => true,
  }),
);

Example query:

query {
  validation(string: "a") {
    __typename
    ... on QueryValidationSuccess {
      data
    }
    ... on ZodError {
      fieldErrors {
        message
        path
      }
    }
  }
}

With the dataloader plugin

To use this in combination with the dataloader plugin, ensure that that errors plugin is listed BEFORE the dataloader plugin in your plugin list.

If a field with errors returns a loadableObject, or loadableNode the errors plugin will now catch errors thrown when loading ids returned by the resolve function.

If the field is a List field, errors that occur when resolving objects from ids will not be handled by the errors plugin. This is because those errors are associated with each item in the list rather than the list field itself. In the future, the dataloader plugin may have an option to throw an error at the field level if any items can not be loaded, which would allow the error plugin to handle these types of errors.

With the prisma plugin

To use this in combination with the prisma plugin, ensure that that errors plugin is listed BEFORE the prisma plugin in your plugin list. This will enable errors option to work correctly with any field builder method from the prisma plugin.

errors can be configured for any field, but if there is an error pre-loading a relation the error will always surfaced at the field that executed the query. Because there are cases that fall back to executing queries for relation fields, these fields may still have errors if the relation was not pre-loaded. Detection of nested relations will continue to work if those relations use the errors plugin

Errors plugin

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