I have several GraphQL queries and mutations, now I'm trying to implement a delete mutation without returning any data:
type Mutation{
addElement(element: ElementData): ID
removeElement(id: ID): ¿?
}
However, it seems to be required to have a return value for the delete operation. Is there a way to perform an "empty" response in GraphQL? I would like to avoid things like returning a boolean or status flag if possible.
I'm not sure on what are the best practices for GraphQL delete operations.
According to this Github issue you cannot return nothing.
You can define a return type which is nullable e.g.
type Mutation {
addElement(element: ElementData): ID
removeElement(id: ID): Boolean
}
But I suggest you return the id of the deleted element, because if you want to work with a cached store you have to update the store when the delete mutation has ran successfully.
(A) Solution with graphql-scalars
The original answer is below.
Here is another one solution with graphql-scalars library:
install npm install graphql-scalars and then
import their Void type: https://www.graphql-scalars.dev/docs/scalars/void
(B) Solution with a custom scalar
Note: design with void-result from mutations goes against "GQL best practices"
This example was written for NodeJS Apollo Framework, but it is pretty easy to convert the implementation for your language/framework
I'm pretty sure: there is an NPM-package named graphql-void but if you don't want to add another one dependency just copy this code.
1. define Void-scalar in your schema
# file: ./schema.gql
scalar Void
2. implement resolver
// file ./scalar-void.js
import { GraphQLScalarType } from 'graphql'
const Void = new GraphQLScalarType({
name: 'Void',
description: 'Represents NULL values',
serialize() {
return null
},
parseValue() {
return null
},
parseLiteral() {
return null
}
})
export Void
3. add the resolver to ApolloServer
Add the Void resolver to the options of your instance of Apollo Server:
# file: ./server.js
import { ApolloServer } from 'apollo-server-express'
import { Void } from './scalar-void'
const server = new ApolloServer({
typeDefs, // use your schema
resolvers: {
Void: Void,
// ... your resolvers
},
})
4. use Void for your mutations in the schema
Finally, use the new scalar in your schema:
# file: ./schema.gql
type Mutation{
addElement(element: ElementData): ID
removeElement(id: ID): Void
}
If you use TypeScript and graphql-codegen:
In the GraphQL schema:
scalar Void
type Mutation {
removeElement(id: ID): Void
}
In the codegen config for resolvers:
config:
scalars:
Void: "void"
With this config TypeScript will ensure that nothing is returned from the removeElement mutation resolver. And the returning value for the mutation will always be null on the GraphQL side.
Check out graphql-scalars Void. This is standard boilerplate for all of my GraphQL projects.
npm i graphql-scalars
Related
I am using Apollo GraphQL server and directives.
Here is my simple schema. Notice the directive on the token field, User type.
const typeDefs = `
directive #allow(service: String) on FIELD_DEFINITION
type User {
email: String!
pass: String!
... other fields here
token: String #allow(service: "login")
}
type Mutation {
login(email: String!, pass: String!): User
}`;
I would like to return the token field only if the login has been called. Otherwise, I would like to return the User object without the token field, all I could find is throwing an Exception or returning the null in the "token" field.
class SkipDirective extends SchemaDirectiveVisitor {
visitFieldDefinition(field, details) {
const { resolve = defaultFieldResolver } = field;
field.resolve = async function (...args) {
// If called in context different from "login"
// Here I would like to just "delete" the "token" field
else {
const result = await resolve.apply(this, args);
return result;
}
};
}
}
Ideas?
If a field is requested, it should be returned with either a value matching the field's type or else null. To do otherwise would break the spec.
There is no way you can modify this behavior through a schema directive. A field definition directive can only change runtime behavior by modifying the field's resolver. However, by the time the resolver is called, the selection set has already been determined so it's too late to modify it. Returning null or throwing an error are pretty much the only two options.
You might be able to implement some kind of workaround through either the formatResponse option or a custom plugin. However, because this behavior would break the spec, there's no telling if it wouldn't cause issues with client libraries or other tools.
the enum define in OrderTypesEnum.gql
enum OrderTypes {
full_buy
pink_buy
}
import OrderTypesEnum.gql file
import OrderTypes from '#/graphql/OrderTypesEnum.gql'`
but, How to get enum in code ?
I use OrderTypes.full_buy get some error:
self.$apollo.mutate({
mutation: createOrder,
variables: {
subjectId: self.subject.id,
types: OrderTypes.full_buy
}
})
Mutation createOrderMutation error: Invariant Violation: Schema type definitions not allowed in queries. Found: "EnumTypeDefinition"
the inspect of OrderTypes type enum
Prerequisites:
< SomeEnumType > is defined in GraphQL schema (server side, no client configuration needed)
Let's assume we have:
enum SomeEnumType {
OPTION1,
OPTION2,
OPTION3
}
Apollo Client should be configured appropriate way and connected with the GraphQL API.
Then on the client side:
export const OUR_MUTATION = gql`
mutation ourMutation($foo: SomeEnumType){
ourMutation(foo: $foo){
bar
}
}
`
Only by doing this, we can pass an enum as a variable in our query or mutation. For example, with useMutation hook we can now mutate as follows:
const [ourMutation] = useMutation(OUR_MUTATION, {
variables: {
foo: "OPTION2"
},
Since the type definition in gql tag equals the definition in Schema, GraphQL recognizes a variable as an enum type despite giving it as a string.
If we want to pass an enum to variables using typescript enums we can do it as follows:
enum SomeEnumType {
OPTION1 = 0,
OPTION2 = 1,
OPTION3 = 2
}
const [ourMutation] = useMutation(OUR_MUTATION, {
variables: {
foo: SomeEnumType[SomeEnumType.OPTION1]
},
UPDATE: String enums and type generation
Personally, I recommend using string enums if possible. The usage of string enums is more straightforward.
enum SomeEnumType {
OPTION1 = "OPTION1",
OPTION2 = "OPTION2",
OPTION3 = "OPTION3"
}
...
...
variables: {
foo: SomeEnumType.OPTION1
}
For next-level coding, enum types, and all other type definitions can be automatically generated to the frontend with graphql-codegen. I really recommend using this approach, since backend schema updates and additions directly can be directly reflected in your frontend code revealing bugs and helping you code faster and more reliable.
As the error message is suggesting, Schema type definitions not allowed in queries., you can't add an enum definition in an operation document (ExecutableDefinition). You can only have operations (query, mutation, or subscription), or fragments definitions. That is, this is invalid:
enum OrderTypes {
FULL_BUY
PINK_BUY
}
mutation createOrderMutation {
...
}
If you want to define a local enum on your client, you can use the typeDefs property during ApolloClient initialization:
const client = new ApolloClient({
cache,
typeDefs: gql`
enum OrderTypes {
FULL_BUY,
PINK_BUY
}
`,
});
And then you'll be able to see the OrderTypes enum on client-side introspection (i.e Apollo extension).
Pay attention to the client-side highlight: if you try to send a request with this enum for a non-client field (i.e without the #client directive) and it makes through your server, you'll get a schema error saying that the enum type does not exist, unless you define it on your backend.
I've been reading through the graphQL docs and found that they've explained the implementation of the graphql server in 2 ways: one using graphql-yoga which is a fully featured graphql server and another one is using graphql, express-graphql and express. In both cases, we pass the schema and resolver functions while creating the server instance.
But the implementation of resolver function differs. While using graphql-yoga, the resolver function is provided with 4 arguments which contains information about the parent object, arguments received, context, info. whereas in the other case (using graphql), the resolver function only gets the arguments object.
Why is that so ? If I want the info, context objects, how do I get it ?
Using graphql-yoga example: https://graphql.org/learn/execution/
Using graphql example: https://graphql.github.io/graphql-js/mutations-and-input-types/
// Code example using graphql
var express = require('express');
var graphqlHTTP = require('express-graphql');
var { buildSchema } = require('graphql');
var schema = buildSchema(`
type Query {
rollDice(numDice: Int!, numSides: Int): [Int]
}
type Mutation {
addDice(numDice: Int): String
}
`);
var root = {
rollDice({numDice, numSides}) {
return [1, 2];
},
addDice({numDice}) {
console.log("Adding something");
return "Added";
}
};
var app = express();
app.use('/graphql', graphqlHTTP({
schema: schema,
rootValue: root,
graphiql: true,
}));
app.listen(4000);
console.log('Running a GraphQL API server at localhost:4000/graphql');
// Code example using graphql-yoga
let graphqlServer = require("graphql-yoga");
const typeDefs = `
type Query {
rollDice(numDice: Int!, numSides: Int): [Int]
}
type Mutation {
addDice(numDice: Int): String
}
`;
const resolvers = {
Query: {
rollDice(parent, args, context, info) {
console.log(args.numDice);
console.log(args.numSides);
return [1, 2];
}
},
Mutation: {
addDice(parent, args, context, info) {
console.log(args.numDice);
return "Added";
}
}
};
const server = new graphqlServer.GraphQLServer({
typeDefs,
resolvers
});
server.start(() => {
console.log("server started on localhost:4000");
});
Difference between these 2 code snippets:
The resolver functions are present inside appropriate types (i.e. Query, Mutation) in one case. In the other case, they are present inside one root object. This means that I can have methods with same name in Query and Mutation in the first case, whereas in the second case that's not possible since they are keys of a single object and keys should be unique.
Why is this so ? Am I basically missing something ? How can the implementation details differ from one package to another ?
REAL TALK: the GraphQL.js docs are not that great. In my opinion, they never should have used examples with buildSchema in the first place because it understandably leads to this kind of confusion.
GraphQL.js (i.e. the graphql package) is the JavaScript implementation of GraphQL. Building a schema in GraphQL.js is done programmatically, by constructing an instance of the GraphQLSchema class:
const userType = new GraphQLObjectType({
name: 'User',
fields: {
id: {
type: GraphQLID,
},
email: {
type: GraphQLString,
},
},
});
const queryType = new GraphQLObjectType({
name: 'Query',
fields: {
user: {
type: userType,
resolve: () => ({ id: 1, email: 'john.doe#example.com' }),
},
},
});
const schema = new GraphQLSchema({
query: queryType,
})
If we print this schema in Schema Definition Language (SDL), it looks like this:
type Query {
user: User
}
type User {
id: ID
email: String
}
Working with SDL is much easier than having to write out all that code. However, GraphQL.js does not provide a way to build a fully-featured schema from SDL. It does provide a buildSchema function, but this utility constructs a schema without any resolvers (and a number of other features like union/interface type resolution).
The graphql-tools package provides a makeExecutableSchema function that lets you build a schema from SDL and a resolver map object. This is what's used under the hood by apollo-server and graphql-yoga. makeExecutableSchema constructs a schema from SDL using buildSchema and then mutates the resulting object, adding the resolvers in after the fact.
In GraphQL.js, the resolve function (or resolver) for a field takes four parameters -- the parent value, the field's arguments, the context and a GraphQLResolveInfo object. If we're creating a GraphQLObjectType like userType in the above example, this is the optional function we can provide for each of the fields in our object. This is the same function you define when you construct a resolver map to use with graphql-yoga. This is the only implementation of a field resolver.
So what's the deal with buildSchema??
The examples in the docs take advantage of GraphQL's default field resolver:
export const defaultFieldResolver: GraphQLFieldResolver<any, *> = function(
source,
args,
contextValue,
info,
) {
if (typeof source === 'object' || typeof source === 'function') {
const property = source[info.fieldName];
if (typeof property === 'function') {
return source[info.fieldName](args, contextValue, info);
}
return property;
}
};
As you can see, the default resolution logic looks for a property with the same name as the field on the source (parent) value. In our example above, the user resolver returns {id: 1, email: 'john.doe#example.com'} -- this is the value the field resolves to. The field is of the type User. We do not have a resolver defined for our id field, so the default resolver does its thing. The id field resolves to 1 because that's the value of the property named id on the parent object the resolver receives.
However, the parent value can also be a function instead of an object. If it's a function, it gets called first and then the return value is used. What does the function get called with? Well, it can't pass it a parent value (because of infinite recursion), but it can pass it the remaining three parameters (args, context and info). So that's what it does.
Now for the magic trick 🎩🐇
In our example, I can omit the resolver for the user field and pass a function to the root value instead.
const root = {
user: () => ({id: 1, email: 'john.doe#example.com'})
}
The root object is just an optional object that's passed down as the parent value to resolvers at the root level (like your Query or Mutation types). Otherwise, those resolvers would not have a parent value.
Query is an operational root type -- it serves as an "entry point" to the rest of your schema. Any fields on the Query type will be passed the root object as the parent value. If I omit a resolver for the user field, the default resolver will 1) examine the parent object for a property with the same name, 2) find a property and determine that it's a function, 3) call the function, 4) resolve the field to the return value of the function.
TADA!
However, because the function is called by the default resolver, and is not used as a resolver itself, it will only receive the three aforementioned parameters, instead of 4.
This is a neat way to work around not being able to actually provide custom resolvers for a schema, but it's very limited. It only works for root types, so we can't similarly provide fake resolvers for User fields or other types. We can't use interfaces or unions in our schema because we can't provide resolveType functions. And so on...
Hopefully that provides some clarity. And hopefully we can get the docs updated in the near future to avoid all this confusion in the first place.
I am using graphql-tools. After receiving a GraphQL query, I execute a search using ElasticSearch and return the data.
However, usually the requested query includes only a few of the possible fields, not all. I want to pass only the requested fields to ElasticSearch.
First, I need to get the requested fields.
I can already get the whole query as a string. For example, in the resolver,
const resolvers = {
Query: {
async user(p, args, context) {
//can print query as following
console.log(context.query)
}
.....
}
}
It prints as
query User { user(id:"111") { id name address } }
Is there any way to get the requested fields in a format like
{ id:"", name:"", address:"" }
In graphql-js resolvers expose a fourth argument called resolve info. This field contains more information about the field.
From the GraphQL docs GraphQLObjectType config parameter type definition:
// See below about resolver functions.
type GraphQLFieldResolveFn = (
source?: any,
args?: {[argName: string]: any},
context?: any,
info?: GraphQLResolveInfo
) => any
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 },
}
In the fieldNodes field you can search for your field and get the selectionSet for the particular field. From here it gets tricky since the selections can be normal field selections, fragments or inline fragments. You would have to merge all of them to know all fields that are selected on a field.
There is an info object passed as the 4th argument in the resolver. This argument contains the information you're looking for.
It can be helpful to use a library as graphql-fields to help you parse the graphql query data:
const graphqlFields = require('graphql-fields');
const resolvers = {
Query: {
async user(_, args, context, info) {
const topLevelFields = graphqlFields(info);
console.log(Object.keys(topLevelFields)); // ['id', 'name', 'address']
},
};
Similarly for graphql-java you may do the same by extending the field parameters with myGetUsersResolverMethod(... DataFetchingEnvironment env).
This DataFetchingEnvironment would be injected for you and you can traverse through this DataFetchingEnvironment object for any part of the graph/query.
This Object allows you to know more about what is being fetched and what arguments have been provided.
Example:
public List<User> getUsers(final UsersFilter filter, DataFetchingEnvironment env) {
DataFetchingFieldSelectionSet selectionSet = env.getSelectionSet();
selectionSet.getFields(); // <---List of selected fields
selectionSet.getArguments(); // <--- Similarly but MAP
...
}
In fact you may be alluding to look ahead data fetching. The above should give you enough insights into the fields requested and you can take it from there to tailor you downstream calls manually. But also you may look into a more efficient way to do this by using the data fetchers for Building efficient data fetchers by looking ahead
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 :)