While I try to learn GraphQL-Tools.I found this article.In this article,example resolvers are described as follows.
const resolvers = {
Query: {
posts: () => posts,
author: (_, { id }) => find(authors, { id })
},
Mutation: {
upvotePost: (_, { postId }) => {
const post = find(posts, { id: postId })
if (!post) {
throw new Error(`Couldn't find post with id ${postId}`)
}
post.votes += 1
return post
}
},
Author: {
posts: author => filter(posts, { authorId: author.id })
},
Post: {
author: post => find(authors, { id: post.authorId })
}
}
I understood that Queryand MutationandSubscriptionis main function of Graphql resolvers.
My question is what is Author,Post in this resolver ?
I can understand QueryandMutationsection of this resolver. but how to think about Authorand Post?
It seems that it defined functions.
Thanks
That is Trival Resolver
https://graphql.org/learn/execution/#trivial-resolvers
Until Graphql has a completely understandable return value.
Graphql goes on to the next search with the returned type.
Those functions [Author, Post] tell to Graphql how to find the object's value.
For exameple if "PostFindById" reoslver promised to graphql that will return "author" field But instead it return "Post" Graphql will excute Trival Rsolver to find value of author field with given "Post".
So it will execute this resolver with given 'post'
Post: {
author: post => find(authors, { id: post.authorId })
}
Related
Let's say I have a simple GraphQL type for a user:
type User {
id: ID!
name: String!
}
Query {
user(id:ID!)
}
and a resolver
user = (_, {id}, {api})=> api.getUser(id)
Now I have add a new field to the User called friends and added a new resolver for the User.friends field.
friends = ({id}, _, {api})=> api.getFriends(id)
So now I wonder when we made a query like this, how can I prevent the call to api.getUser but only call api.getFriends.
query {
user(id){
friends {
name
}
}
}
My understanding is that having a resolver defined for the user field in the Query type, it will always call this resolver first and after that all resolvers for fields in the User type.
This is a common problem and there is for example this solution out there: https://github.com/gajus/graphql-lazyloader
Check out the README of the project for a structured description of your problem.
Alternatively, you can implement your own class that contains a cached value making use of how GraphQL.js implements default resolvers:
class User {
constructor(id) {
this.id = id;
}
getInstance({ api }) {
if (!this.instance) {
this.instance = api.getUser(this.id);
}
return this.instance;
}
// notice how id is already a property of this class
name(args, ctx) {
return this.getInstance(ctx).then(instance => instance.name);
}
// do the same for other fields, user will only be fetched once.
friends(args, { api }) {
return api.getFriends(this.id);
}
}
const resolvers = {
Query: {
user: (args) => new User(args.id),
}
}
If you use dataloader you can even do this with even less code thanks to caching in dataloader:
// You probably have this function already somewhere in your apollo server creation
function createContext({ api }) {
return {
api,
loaders: {
user: new Dataloader((ids) => ids.map(id => api.getUser(id))),
},
}
}
const resolvers = {
Query: {
user: (parent, args) => ({ id: args.id }),
},
User: {
name: ({ id }, args, { loaders }) =>
loaders.user.load(id).then(user => user.name),
otherProp: ({ id }, args, { loaders }) =>
loaders.user.load(id).then(user => user.otherProp),
friends: ({ id }, args, { api })=> api.getFriends(id),
}
}
Dataloader will, even when called twice, only reach to the API once. An added benefit is, that it will cache the value. Ideally, you even provide a batch load function in the API to make the loader even more efficient.
Be aware, that user.fields.name now makes calls for every friend to the API. To avoid that, you could check if the property exists:
name: (parent, args, { loaders }) =>
parent.name ?? loaders.user.load(parent.id).then(user => user.name),
I am creating a Next.js blog that uses an API created with KeystoneJS. I am extremely confused by how I can get an individual post on a dynamic route from the post's slug.
The Query
This is how I thought the query should be:
query Post($slug: String) {
Post(where: { slug: $slug }) {
id
}
}
And this was queried like so in a file called post.service.js:
export async function getBySlug(slug) {
return apolloClient
.query({
query: gql`
query Post($slug: String) {
Post(where: { slug: $slug }) {
id
}
}
`,
})
.then((result) => {
return result.data.Post;
});
}
Unsurprisingly, that causes an ApolloError because how would the query know what slug to query the API for when accessing posts/[slug].js?
It's also worth noting that KeystoneJS say on their guides that:
The single entity query accepts a where parameter which must provide an id.
How would I pass the post's ID to the query depending on what slug was accessed at [slug].js and does this mean I can't query by the slug at all?
On [slug].js I am using getStaticPaths() and getStaticProps() like this:
export async function getStaticPaths() {
const posts = await getAll();
const paths = posts.map((post) => ({
params: { slug: post.slug },
}));
return { paths, fallback: false };
}
export async function getStaticProps({ params }) {
const term = await getBySlug(params.slug);
return { props: { post } };
}
How can I do this?
If you're using a where clause rather than matching on id, you have to query allPosts rather than Post.
A tested example, matching a user by their email address:
query($email: String!) {
allUsers(where : {email: $email}){
id
}
}
Variables:
{
"email": "user#email.com"
}
So I think you want:
query($slug: String!) {
allPosts(where: {slug: $slug}) {
id
}
}
I have a problem, thx for any help.
With prisma we can use include with where conditions for models with a relation. If I make include conditions I get the right result. If I return it to the frontend it gets overwritten. I want to return exact my result from the backend.
I have at the frontend a query (ApolloClient, gql) like. It will return an array of comments for each post, I just want to have the first Comment for each post.
const POSTS = gql`
query posts {
posts(postId: $postId) {
id
comments{ // at the backend I have conditions for the comments
id
}
}
}
`;
Backend: Primsa and graphql nexus
Prisma Schema
model Post {
id String #id #default(cuid())
comments Comment[]
}
model Comment {
id String #id #default(cuid())
post Post #relation(fields: [postId], references: [id])
postId String
}
Nexus Model
const Post = objectType({
name: 'Post',
definition(t) {
t.model.id()
t.model.comments()
})
const Comment = objectType({
name: 'Comment',
definition(t) {
t.model.id()
t.model.post()
t.model.postId()
})
Resolver
export const posts = queryField('posts', {
type: 'Post',
list: true,
args: {
...
},
resolve: async (_parent, args: any, { prisma, request }, info) => {
const posts = await prisma.post.findMany({
include: {
comments: {
take: 1
}
}
})
console.log(posts)
//Perfect result I want to return the include condition. But at the frontend I have all
//comments
return posts
},
})
The console.log(posts) is exact what I want to return!. Every post has an Array of ONE Comment.
I return the posts and at the frontend every post has an Array of ALL Comments, what I don't want. How can I prevent that the frontend query overwrite the backend return? The fields are the same.
I can't add a comment, so I am adding this to another answer.
Like I said with my PrismaSelect plugin, you can't use nexus-plugin-prisma t.model, t.crud. You will need to use Pal.Js CLI to autoGenerate all CRUD and ObjectTypes for all models.
const Post = objectType({
name: 'Post',
definition(t) {
t.model.id()
t.model.comments() // this field will overwritten by next one so this not needed
t.list.field('comments', {
type: 'Comment',
list: true,
resolve: (parent, args, { prisma }) => {
// here parent type include all other fields but not this field
return prisma.comment.findMany({ // this query is very wrong will case N+1 issue
where: {
postId: parent.id,
},
take: 1,
})
},
})
})
Example
model User {
id Int #default(autoincrement()) #id
createdAt DateTime #default(now())
email String #unique
name String?
password String
posts Post[]
comments Comment[]
}
model Post {
id Int #default(autoincrement()) #id
published Boolean #default(false)
title String
author User? #relation(fields: [authorId], references: [id])
authorId Int?
comments Comment[]
}
model Comment {
id Int #default(autoincrement()) #id
contain String
post Post #relation(fields: [postId], references: [id])
postId Int
author User? #relation(fields: [authorId], references: [id])
authorId Int?
}
Here is my Pal.Js CLI generated type for Post model
import { objectType } from '#nexus/schema'
export const Post = objectType({
name: 'Post',
definition(t) {
t.int('id', { nullable: false })
t.boolean('published', { nullable: false })
t.string('title', { nullable: false })
t.field('author', {
nullable: true,
type: 'User',
resolve(parent: any) {
return parent['author']
},
})
t.int('authorId', { nullable: true })
t.field('comments', {
nullable: false,
list: [true],
type: 'Comment',
args: {
where: 'CommentWhereInput',
orderBy: 'CommentOrderByInput',
cursor: 'CommentWhereUniqueInput',
take: 'Int',
skip: 'Int',
distinct: 'CommentDistinctFieldEnum',
},
resolve(parent: any) {
return parent['comments']
},
})
},
})
when you use my Pal.js CLI, your frontend request will be like this
query {
findOnePost(where: {id: 1}) {
comments(where: {}, take: 1){
id
}
}
}
``
The best way to handle this issue and just query what your frontend request to use my PrismaSelect plugin.
Prisma Select takes the info: GraphQLResolveInfo object in general graphql arguments (parent, args, context, info) to select object accepted by prisma client. The approach allows a better performance since you will only be using one resolver to retrieve all your request. By doing so, it also eliminates the N + 1 issue.
Also, you can use my CLI to autogenerate all CRUD from your schema.prisma file https://paljs.com/generator/nexus
I mean I can add to my Post-ObjectType a field condition like:
const Post = objectType({
name: 'Post',
definition(t) {
t.model.id()
t.model.comments()
t.list.field('comments', {
type: 'Comment',
list: true,
resolve: (parent, args, { prisma }) => {
return prisma.comment.findMany({
where: {
postId: parent.id,
},
take: 1,
})
},
})
})
This is working. But if I understood it correct I have for every post one extra request. But I have already at the mutation resolver the right result. And I don't have the comments field at the parent (t.list.field- resolver)
I am querying my graphql backend and need the response to have a flatten shape,
my query:
gql`
{
questions {
edges {
id
title
author: user {
email
}
}
}
}
`
my response:
'5d3eafb7889a135ff8cd950c': {
id: '5d3eafb7889a135ff8cd950c',
title: 's',
author: {
email: 'dggdfgdgfd#gmail.com',
__typename: 'User'
},
__typename: 'Question'
},
problem is with author, I need as a string instead of an object:
id: '5d3eafb7889a135ff8cd950c',
title: 's',
author: 'dggdfgdgfd#gmail.com' // <===
`
You have two options:
1) After getting the data from the GraphQL server, transform the data as you need to fit your needs. A Javascript implementation might be:
function flattenGqlResponse (response) {
return Object.keys(response).map((question) => {
return {
id: response[question].id,
title: response[question].title,
author: response[question].author.email
}
}
);
}
2) Flatten the structure in your GraphQL Resolver on your GraphQL Server. Likely, you do not want to pursue this route based on what I see about your schema, unless your User object only has one field, that is email
Going off Apollo's cacheRedirect example (https://www.apollographql.com/docs/react/advanced/caching.html#cacheRedirect)
Now, I make the following schema modification...
type Query {
books: [BookPayload!]!
}
type BookPayload {
books: [Book!]!
// other stuff, e.g. bookCount: Int
}
In the example, Apollo can check if any returned books are in the cache by:
cacheRedirects: {
Query: {
books: (_, args, { getCacheKey }) =>
args.ids.map(id =>
getCacheKey({ __typename: 'Book', id: id }))
}
}
However, I'm not sure how to redirect the cache when the type being checked isn't directly returned. I've tried every permutation of return to no avail.
Any help is really appreciated. Thanks!
You're question is unclear. You say "I'm not sure how to redirect the cache when the type being checked isn't directly returned," but you appear to be checking and returning [BookPayload!]!
Therefore I see no reason why this wouldn't work:
cacheRedirects: {
Query: {
books: (_, args, { getCacheKey }) =>
args.ids.map(id =>
getCacheKey({ __typename: 'BookPayload', id: id }))
}
}