hayes
Errors Plugin
A plugin for easily including error types in your GraphQL schema and hooking up error types to resolvers
Usage
Install
yarn add @giraphql/plugin-errorsSetup
Ensure that the target in your tsconfig.json is set to es6 or higher (default is es3).
Example Usage
import ErrorsPlugin from '@giraphql/plugin-errors';
const builder = new SchemaBuilder({
plugins: [ErrorsPlugin],
errorOptions: {
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 fordirectResultoption on fields (only affects non-list fields)
Options on Fields
types: An array of Error classes to catch and handle as error objects in the schema. Will be merged withdefaultTypesfrom builder.union: An options object for the union type. Can include any normal union type options, andnameoption for setting a custom name for the union type.result: An options object for result object type. Can include any normal object type options, andnameoption 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 nameddataby default, but can be written by passsing a customnameoption.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
defaultTypesin 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 '@giraphql/plugin-errors';
const builder = new SchemaBuilder({
plugins: [ErrorsPlugin],
errorOptions: {
defaultTypes: [Error],
},
});
const ErrorInterface = builder.interfaceRef<Error>('Error').implement({
fields: (t) => ({
message: t.exposeString('message'),
}),
});
builder.objectType(Error, {
name: 'BaseError',
isTypeOf: (obj) => obj instanceof Error,
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],
isTypeOf: (obj) => obj instanceof LengthError,
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 }[] {
// eslint-disable-next-line no-underscore-dangle
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],
isTypeOf: (obj) => obj instanceof ZodError,
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 validation 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.
plugin. This is because if items are nullable, the items in the list may be set to null rather that
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 validation plugin in your plugin list. This will enable errors option to work 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