How to create field resolver on RedwoodJS - redwoodjs

Question

RedwoodJS automatically maps GraphQL queries resolvers to api/src/services. How do I create a field resolver for a given GraphQL type?
Suppose I have this schema:
type Person {
name: string!
birthDate: DateTime!
age: Int!
}
But only name and birthDate are stored in the database.
Using graphql-tools I would write my resolvers like this:
const resolvers = {
Query: { ... },
Mutation: { ... },
Person: {
age(person) {
return new Date().getFullYear() - person.birthDate.getFullYear();
},
},
};
PS: I know the age formula is wrong.
PS2: I'm using age here for the sake of simplicity, imagine this is expensive to compute or get from database.

Answer 1

It's almost identical to the way you do it with graphql-tools.
You export an object with the same name as your type in your service:
// services/person.js
export const Person = {
age: (_args, { root }) {
return new Date().getFullYear() - root.birthDate.getFullYear();
},
}
As an aside, you could also export a resolvers in the person.sdl.js file (But services take precendence):
// graphql/person.sdl.js
export const schema = gql`/* ... */`
export const resolvers = {
Query: {},
Mutation: {},
Person: {},
}

Answer 2

Edit: I misunderstood the question, this answer just covers creating query + mutation resolvers, not a resolver for a computed field.
To create a field resolver, you'll need to decide whether you're creating a resolver for a query, or a handler for a mutation.
We can use the following schema as an example:
export const schema = gql`
type Person {
id: String!
name: String!
age: Int!
}
type PersonInput {
name: String
age: Int
}
type Mutation {
createPerson(input: PersonInput!): Person
}
type Query {
people: [Person]
person(id: String!): Person
}
`
If the above schema is stored in a file called persons.sdl.js, in the api/src/graphql directory, you can implement the queries and mutations in a file called persons.js in the api/src/services/persons directory.
// implements Mutation.createPerson(...)
export const createPerson({ input }) => {
return db.person.create({
data: input
})
}
// implements Query.people
export const people = () => {
return db.person.findMany()
}
// implements Query.person(...)
export const person = ({ id }) => {
return db.person.findOne({
where: { id }
})
}