Formatting responses.md

Formatting REST responses

By default, non-error responses (operation completed successfully, "data" object has at least one non-null property), are formatted to look like standard REST responses. That is, a flat JSON object or array, with no extra 'errors' array; if one (but not all) of the resolvers encountered an error and returned null, that field in the response will be null.

Upon error (operation did not complete successfully, "data" object is undefined or has only null properties) the REST API will return an object with the original errors array from GraphQL.

The format of both successful responses and error responses can be modified by providing init() with formatErrorFn or formatDataFn functions.

Each of these function receives the original response from GraphQL, and returns a modified JSON response that will be sent to the client via REST API.

formatErrorFn also receives the HTTP status code that the REST API sends to the client.

Example:

/* this function will be called to format all errors emitted by GraphQL before sent out via REST API */
const formatError = (graphQlErrorObj, httpStatusCode = 500) => {
    const err = graphQlErrorObj;
    if (!err || typeof err !== 'object' || !err.errors || !Array.isArray(err.errors)) return err;
    const firstError = err.errors[0];
    if (!firstError || typeof firstError !== 'object') return err;
    
    return {
        message: firstError.message || 'General error',
        status: httpStatusCode
    }
}

And call init() with:

const restRouter = GraphQL2REST.init(schema, execute, options, formatError);

Note: If you change the structure of the error response you might need to edit the value of the field "graphqlErrorCodeObjPath" in the options object passed to init(), so as to set the new location of the "code" property in the object if it has changed (by default, it is set to (errorResponse).errors[0].extensions.code). This field is used to map GraphQL error codes to HTTP status codes when an erroneous response is returned.

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Learn more about:

• Filtering and shaping the responses on the client side
• Using apollo-link to work with a remote GraphQL server

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