I have written a GraphQL query which like the one below:
{
posts {
author {
comments
}
comments
}
}
I want to know how can I get the details about the requested child fields inside the posts resolver.
I want to do it to avoid nested calls of resolvers. I am using ApolloServer's DataSource API.
I can change the API server to get all the data at once.
I am using ApolloServer 2.0 and any other ways of avoiding nested calls are also welcome.
You'll need to parse the info object that's passed to the resolver as its fourth parameter. This is the type for the object:
type GraphQLResolveInfo = {
fieldName: string,
fieldNodes: Array<Field>,
returnType: GraphQLOutputType,
parentType: GraphQLCompositeType,
schema: GraphQLSchema,
fragments: { [fragmentName: string]: FragmentDefinition },
rootValue: any,
operation: OperationDefinition,
variableValues: { [variableName: string]: any },
}
You could transverse the AST of the field yourself, but you're probably better off using an existing library. I'd recommend graphql-parse-resolve-info. There's a number of other libraries out there, but graphql-parse-resolve-info is a pretty complete solution and is actually used under the hood by postgraphile. Example usage:
posts: (parent, args, context, info) => {
const parsedResolveInfo = parseResolveInfo(info)
console.log(parsedResolveInfo)
}
This will log an object along these lines:
{
alias: 'posts',
name: 'posts',
args: {},
fieldsByTypeName: {
Post: {
author: {
alias: 'author',
name: 'author',
args: {},
fieldsByTypeName: ...
}
comments: {
alias: 'comments',
name: 'comments',
args: {},
fieldsByTypeName: ...
}
}
}
}
You can walk through the resulting object and construct your SQL query (or set of API requests, or whatever) accordingly.
Here, are couple main points that you can use to optimize your queries for performance.
In your example there would be great help to use
https://github.com/facebook/dataloader. If you load comments in your
resolvers through data loader you will ensure that these are called
just once. This will reduce the number of calls to database
significantly as in your query is demonstrated N+1 problem.
I am not sure what exact information you need to obtain in posts
ahead of time, but if you know the post ids you can consider to do a
"look ahead" by passing already known ids into comments. This will
ensure that you do not need to wait for posts and you will avoid
graphql tree calls and you can do resolution of comments without
waiting for posts. This is great article for optimizing GraphQL
waterfall requests and might you give good idea how to optimize your
queries with data loader and do look ahead
https://blog.apollographql.com/optimizing-your-graphql-request-waterfalls-7c3f3360b051
Related
From Redux docs:
This [normalized] state structure is much flatter overall. Compared to
the original nested format, this is an improvement in several ways...
From https://github.com/paularmstrong/normalizr
:
Many APIs, public or not, return JSON data that has deeply nested objects. Using data in this kind of structure is often very difficult for JavaScript applications, especially those using Flux or Redux.
Seems like normalized database-ish data structures are better to work with on front end. Then why GraphQL is so popular if it's whole language style is revolved around quickly getting any nested data? Why do people use it then?
This kind of discussion is off-topic on SO ...
it's not only about [normalized] structures ...
graphql client (like apollo) takes care of all data fetching related nuances (error handling, cache, refetching, data conversion, and many more) also but hardly doable with redux.
Different use cases, you can use both:
keep (complex) app state in redux,
handle data fetching in apollo (you can use it for local state, too).
Let's look at why we want to normalize the cache and what kind of work we have to do to get a normalized cache.
For the main page we fetch a list of TODOs and a list of high priority TODOS. Our two endpoints return the following data:
{
all: [{ id: 1, title: "TODO 1" }, { id: 2, title: "TODO 2" }, { id: 2, title: "TODO 2"}],
highPrio: [{ id: 1, title: "TODO 1" }]
}
If we would store the data like this into our cache, we have a difficult time updating a single todo, because we have to update the todo in every array we have in our store or might have in our store in the future.
We can normalize the data and only store references in the array. This way we can easily update a single todo in a single place:
{
queries: {
all: [{ ref: "Todo:1" }, { ref: "Todo:2" }, { ref: "Todo:2" }],
highPrio: [{ ref: "Todo:1" }}]
},
refs: {
"Todo:1": { id: 1, title: "TODO 1" },
"Todo:2": { id: 2, title: "TODO 2" },
"Todo:3": { id: 3, title: "TODO 3" }
}
}
The downside is, that this shape of data is now much harder to use in our list component. We will have to transform the cache a lot, roughtly like so:
function denormalise(cache) {
return {
all: cache.queries.all.map(({ ref }) => cache.ref[ref]),
highPrio: cache.queries.highPrio.map(({ ref }) => cache.ref[ref]),
};
}
Notice how now updating Todo:1 inside of the cache will update all queries that reference the todo automatically, if we run this function inside of the React component (this is often called a selector in Redux).
The magical thing about GraphQL is that it is a strict specification with a type system. This allows GraphQL clients like Apollo to globally identify objects and normalise that cache. At the same time it can also automatically denormalise the cache for you and update objects in the cache automatically after a mutation. This means that most of the time you have to write no caching logic at all. And this should explain why it is so popular: The best code is no code!
const { data, loading, error } = useQuery(gql`
{ all { id title } highPrio { id title }
`);
This code automatically fetches the query on load, normalizes the response and writes it into the cache. Then denormalizes the cache back into the shape of the query using the cache data. Updates to elements in the cache automatically update all subscribed components.
We are in the situation that the response of our GraphQL Query has to return some dynamic properties of an object. In our case we are not able to predefine all possible properties - so it has to be dynamic.
As we think there are two options to solve it.
const MyType = new GraphQLObjectType({
name: 'SomeType',
fields: {
name: {
type: GraphQLString,
},
elements: {
/*
THIS is our special field which needs to return a dynamic object
*/
},
// ...
},
});
As you can see in the example code is element the property which has to return an object. A response when resolve this could be:
{
name: 'some name',
elements: {
an_unkonwn_key: {
some_nested_field: {
some_other: true,
},
},
another_unknown_prop: 'foo',
},
}
1) Return a "Any-Object"
We could just return any object - so GraphQL do not need to know which fields the Object has. When we tell GraphQL that the field is the type GraphQlObjectType it needs to define fields. Because of this it seems not to be possible to tell GraphQL that someone is just an Object.
Fo this we have changed it like this:
elements: {
type: new GraphQLObjectType({ name: 'elements' });
},
2) We could define dynamic field properties because its in an function
When we define fields as an function we could define our object dynamically. But the field function would need some information (in our case information which would be passed to elements) and we would need to access them to build the field object.
Example:
const MyType = new GraphQLObjectType({
name: 'SomeType',
fields: {
name: {
type: GraphQLString,
},
elements: {
type: new GraphQLObjectType({
name: 'elements',
fields: (argsFromElements) => {
// here we can now access keys from "args"
const fields = {};
argsFromElements.keys.forEach((key) => {
// some logic here ..
fields[someGeneratedProperty] = someGeneratedGraphQLType;
});
return fields;
},
}),
args: {
keys: {
type: new GraphQLList(GraphQLString),
},
},
},
// ...
},
});
This could work but the question would be if there is a way to pass the args and/or resolve object to the fields.
Question
So our question is now: Which way would be recommended in our case in GraphQL and is solution 1 or 2 possible ? Maybe there is another solution ?
Edit
Solution 1 would work when using the ScalarType. Example:
type: new GraphQLScalarType({
name: 'elements',
serialize(value) {
return value;
},
}),
I am not sure if this is a recommended way to solve our situation.
Neither option is really viable:
GraphQL is strongly typed. GraphQL.js doesn't support some kind of any field, and all types defined in your schema must have fields defined. If you look in the docs, fields is a required -- if you try to leave it out, you'll hit an error.
Args are used to resolve queries on a per-request basis. There's no way you can pass them back to your schema. You schema is supposed to be static.
As you suggest, it's possible to accomplish what you're trying to do by rolling your own customer Scalar. I think a simpler solution would be to just use JSON -- you can import a custom scalar for it like this one. Then just have your elements field resolve to a JSON object or array containing the dynamic fields. You could also manipulate the JSON object inside the resolver based on arguments if necessary (if you wanted to limit the fields returned to a subset as defined in the args, for example).
Word of warning: The issue with utilizing JSON, or any custom scalar that includes nested data, is that you're limiting the client's flexibility in requesting what it actually needs. It also results in less helpful errors on the client side -- I'd much rather be told that the field I requested doesn't exist or returned null when I make the request than to find out later down the line the JSON blob I got didn't include a field I expected it to.
One more possible solution could be to declare any such dynamic object as a string. And then pass a stringified version of the object as value to that object from your resolver functions. And then eventually you can parse that string to JSON again to make it again an object on the client side.
I'm not sure if its recommended way or not but I tried to make it work with this approach and it did work smoothly, so I'm sharing it here.
I'm working with GraphQL and having some trouble finding the best way to pipe variables from the query to the result.
I have a schema like so:
type Fragment {
# The id of the fragment
id: String!
# The key of the fragment
key: String!
# The type of component
component_type: String!
# The params used to build the fragment
params: JSON
# Component data
data: JSON
children: [JSON]
items: [JSON]
}
The fragment is meant as a "cms" fragment. I want to pass some query data through to another backend after this resolves.
My query looks like this:
query getFragmentsWithItems($keys: [String!]!
$platform: PlatformType
$version: String
$userInfo: UserInput
$userId: Int
) {
fragmentsWithItems(keys: $keys, platform: $platform, version: $version, userInfo: $userInfo, userId: $userId) {
key
data
children
params
items
}
}
Here's the problem: I have some query data in the data field from the Fragment. That data is not available until that Fragment has resolved. I want to take that data and send it to a different backend. I want to do this with GraphQL, and I was hoping to do something like:
Fragment: () => {
async query(obj, args, context, info, {modles}) => {
const items = await models.getItems(obj.query_string);
}
}
But I need the user_info and user_id that I passed to the original query. Apparently that is only accessible from the info argument which is not meant to be used.
The other path I've taken is to have a manual resolver that does something like so:
const resolveFI = ({ keys, platform, version, userInfo, userId, models }) => {
if (!keys || !keys.length) {
return Promise.resolve(null);
}
return models.release.get({ platform, version }).then(release =>
Promise.all(
keys.map(key =>
models.fragments.get({
key,
platform,
version,
release: release.id
})
)
).then(data => {
const promises = [];
data.rows.forEach(r => {
if (r.data.query_data) {
const d = {
// Can just ignore
filters: r.data.query_data.filters || {},
user_info: userInfo,
user_id: userId
};
promises.push(
new Promise(resolve => {
resolve(
models.itemSearch.get(d).then(i => ({ items: i.items, ...r }))
);
})
);
}
...etc other backends
This works, however a manual promise chain seems to defeat the purpose of using GraphQL.
The last thing I tried was making items a non-scalar type, something like:
type Fragment {
items: ItemSearchResult(user_info: UserInput) etc
But since I can't pipe the actual result from Fragment to the ItemSearchResult that doesn't work.
I realize this is pretty long-winded so I'm open to edits or clarifying.
I'm looking to see if I've missed a better approach or if I should just bag it and have the client apps do the item query after they get the Fragment data back.
It's not that you're not supposed to use info -- it's just a tremendous pain in the butt to use ;) In all seriousness, it's meant to be used for optimization and more advanced use cases, so you shouldn't hesitate to use it if a better solution doesn't present itself. There are libraries out there (like this one) that you can use to parse the object more easily.
That said, there's a couple of ways I imagine you could handle this:
1.) Inside your query resolver(s)
getFragmentsWithItems: async (obj, args, ctx, info) => {
const fragments = await howeverYouDoThat()
const backendCalls = fragments.map(fragment => {
// extract whatever data you need from the fragment
return asyncCallToBackEnd()
})
await backendCalls
return fragments
}
Unfortunately, if you have a lot of different queries returning fragments, you'll end up with redundancy.
2.) Inside the resolver for an existing field (or an additional one) on the Fragment type.
If you go this route, and you need args passed to the query field, you can extract them using the info. Alternatively, you can also mutate the context object inside your query resolver and attach those arguments to it. Then, all resolvers "below" the query resolver (like the resolvers for your Fragment fields) can access those arguments through the context.
3.) Apollo Server lets you define a formatResponse function when configuring its middleware. This essentially provides a hook to do whatever you want with the response before it's returned to the client. You could parse the response inside that function and make the calls to the other backend from there.
I've been playing with GraphQL recently, and am currently learning about mutations. I'm a bit confused with something. I have a model Post with relation Comments. I have a mutation that looks like this:
mutation addCommentToPost {
updatePost(
id: "POST-1",
comments: [{
body: "Hello!"
}]
) {
id,
comments {
id,
body
}
}
}
The problem is, whenever I run this, it seems to remove all the comments and sets the comments to only the one I just added. To be more specific, how do I write a mutation that pushes to the comments array rather than replacing it?
You are using a mutation called updatePosts, which I assume (based on the name) simply updates a post by replacing the fields that are passed. If you want to use the updatePosts mutation to add a comment, you will first have to query for the post to get the current list of comments, add your comment to the end, and then call updateComment with the entire list of comments (including the one that you just added to the end).
However, this isn't really a good solution, especially if the list of comments is potentially very long. If you have the ability to change the GraphQL server, you should create a new mutation on the server with a signature like addComment(postId: ID, comment: CommentInput). In the resolve function for that mutation, simply add the comment that is passed to the end of the list of current comments.
// resolver for addComment:
addComment(root, args) {
// validate inputs here ...
const post = db.getPost(args.postId);
post.comments.append(args.comment);
db.writePost(post.id, post);
}
db.getPost and db.writePost are functions you have to define yourself to retrieve/write a post from/to wherever you store it.
It's important to note that unlike a SQL or Mongo query, a GraphQL mutation itself doesn't have any meaning without the resolve functions. What the mutation does is defined entirely inside its resolve function. Mutation names and arguments only gain meaning together with the resolve function. It's up to you (or the GraphQL server developers in your company) to write the resolve functions.
The way this situation is currently solved in the Graphcool API is to use a create mutation for the Comment that links to the Post. This is called a nested connect mutation.
This is how it would look like:
mutation {
createComment(
text: "Hello!"
postId: "POST-1"
) {
id
text
post {
comments {
id
}
}
}
}
In the future, other nested arguments like comments_set or comments_push could be introduced, then pushing would be possible like this:
mutation addCommentToPost {
updatePost(
id: "POST-1",
comments_push: [{
body: "Hello!"
}]
) {
id,
comments {
id,
body
}
}
}
Disclosure: I work at Graphcool.
You can use those code as an example for mutation.
module.exports = (refs) => ({
type: refs.commentType,
args: {
id: {
type: GraphQLString
},
body: {
type: GraphQLString
}
},
resolve: (parent, args, root) => {
return createUser(args);
}
});
Good day im newbie here and im tackling graphql and im having some problem on mutation can someone explain this block of code for me thank you
RootMutation: {
createAuthor: (root, args) => { return Author.create(args); },
createPost: (root, { authorId, tags, title, text }) => {
return Author.findOne({ where: { id: authorId } }).then( (author) => {
console.log('found', author);
return author.createPost( { tags: tags.join(','), title, text });
});
},
},
Sure, this is an example of two mutations in a GraphQL server. We can break it down to understand what is going on.
First let's look at the type system. A GraphQL schema normally has two root fields query and mutation (and sometimes subscription). These root fields are the root of your data hierarchy and expose the queries (GET requests) and mutations (POST, PUT, DELETE, etc requests) that you have access to.
By the looks of it you are implementing a schema with a root mutation type that looks like this:
type Mutation {
createAuthor: Author
createPost: Post
}
A type in GraphQL is made up of a set of fields each of which can have an associated resolver. Resolvers in GraphQL are like the event handlers you would attach to endpoints in REST.
The code that you have above is defining two resolvers that will handle the logic associated with the createAuthor and createPost mutations. I.E. the code in the createPost resolver is what will be run when I issue a query like this:
mutation CreatePost($post: CreatePostInput!) {
createPost(input: $post) {
id
title
tags
text
}
}
The GraphQL runtime parses the query and routes the operation to the correct resolver depending on the content of the query. In this example, it would see that I am calling the createPost mutation and would make sure to call the createPost resolver which in your case looks like this:
createPost: (root, { authorId, tags, title, text }) => {
return Author.findOne({ where: { id: authorId } }).then( (author) => {
console.log('found', author);
return author.createPost( { tags: tags.join(','), title, text });
});
},
To understand how a resolver works, let's look at the GraphQLFieldResovler type definition from graphql-js
export type GraphQLFieldResolver<TSource, TContext> = (
source: TSource,
args: { [argName: string]: any },
context: TContext,
info: GraphQLResolveInfo
) => mixed;
As you can see a GraphQLFieldResolver is a function that takes 4 arguments.
source: The source is the parent object of the current field. For example if you were defining a resolver for a field fullName on the User type, the source would be the full user object.
args: The args are any input arguments for that resolver. In my query above it would contain the value of the $post variable.
context: Context is a global context for a GraphQL execution. This is useful for passing information around that a resolver might need. For example, you include a database connection that you can use from your resolvers without importing it in every file.
info: The info object contains information about your GraphQL schema, the query, and other information such as the path to the current resolver being executed. This is useful in many ways. Here is one post talking about how you can use it to precompute queries: (https://scaphold.io/community/blog/querying-relational-data-with-graphql/)
This idea of having types and field resolvers is part of what makes GraphQL so powerful. Once you've defined you type system and the resolvers for their fields you can structure your schema however you want and GraphQL will always make sure to call the correct resolver no matter how deeply nested a query might be.
I hope this helps :)