builder.hook(

"GraphQLObjectType:fields:field",

(

field,

{ pgSql: sql },

{ scope: { isRootMutation, fieldName }, addArgDataGenerator }

) => {

if (!isRootMutation || fieldName !== "createLink") {

// If it's not the root mutation, or the mutation isn't the 'createLink'

// mutation then we don't want to modify it - so return the input object

// unmodified.

return field;

}

// We're going to need link.id for our `performAnotherTask`; so we're going

// to abuse addArgDataGenerator to make sure that this field is ALWAYS

// requested, even if the user doesn't specify it. We're careful to alias

// the result to a field that begins with `__` as that's forbidden by

// GraphQL and thus cannot clash with a user's fields.

addArgDataGenerator(() => ({

pgQuery: queryBuilder => {

queryBuilder.select(

// Select this value from the result of the INSERT:

sql.query`${queryBuilder.getTableAlias()}.id`,

// And give it this name in the result data:

"__createdRecordId"

);

},

}));

// It's possible that `resolve` isn't specified on a field, so in that case

// we fall back to a default resolver.

const defaultResolver = obj => obj[fieldName];

// Extract the old resolver from `field`

const { resolve: oldResolve = defaultResolver, ...rest } = field;

return {

// Copy over everything except 'resolve'

...rest,

// Add our new resolver which wraps the old resolver

async resolve(...resolveParams) {

// Perform some validation (or any other action you want to do before

// calling the old resolver)

const RESOLVE_ARGS_INDEX = 1;

const { input: { link: { title } } } = resolveParams[

RESOLVE_ARGS_INDEX

];

if (title.length < 3) {

throw new Error("Title is too short!");

}

// Call the old resolver (you SHOULD NOT modify the arguments it

// receives unless you also manipulate the AST it gets passed as the

// 4th argument; which is quite a lot of effort) and store the result.

const oldResolveResult = await oldResolve(...resolveParams);

// Perform any tasks we want to do after the record is created.

await performAnotherTask(oldResolveResult.data.__createdRecordId);

// Finally return the result.

return oldResolveResult;

},

};

}

);