I have an graphql/apollo-server/graphql-yoga endpoint. This endpoint exposes data returned from a database (or a REST endpoint or some other service).
I know my data source is returning the correct data -- if I log the result of the call to the data source inside my resolver, I can see the data being returned. However, my GraphQL field(s) always resolve to null.
If I make the field non-null, I see the following error inside the errors array in the response:
Cannot return null for non-nullable field
Why is GraphQL not returning the data?
There's two common reasons your field or fields are resolving to null: 1) returning data in the wrong shape inside your resolver; and 2) not using Promises correctly.
Note: if you're seeing the following error:
Cannot return null for non-nullable field
the underlying issue is that your field is returning null. You can still follow the steps outlined below to try to resolve this error.
The following examples will refer to this simple schema:
type Query {
post(id: ID): Post
posts: [Post]
}
type Post {
id: ID
title: String
body: String
}
Returning data in the wrong shape
Our schema, along with the requested query, defines the "shape" of the data object in the response returned by our endpoint. By shape, we mean what properties objects have, and whether those properties' values' are scalar values, other objects, or arrays of objects or scalars.
In the same way a schema defines the shape of the total response, the type of an individual field defines the shape of that field's value. The shape of the data we return in our resolver must likewise match this expected shape. When it doesn't, we frequently end up with unexpected nulls in our response.
Before we dive into specific examples, though, it's important to grasp how GraphQL resolves fields.
Understanding default resolver behavior
While you certainly can write a resolver for every field in your schema, it's often not necessary because GraphQL.js uses a default resolver when you don't provide one.
At a high level, what the default resolver does is simple: it looks at the value the parent field resolved to and if that value is a JavaScript object, it looks for a property on that Object with the same name as the field being resolved. If it finds that property, it resolves to the value of that property. Otherwise, it resolves to null.
Let's say in our resolver for the post field, we return the value { title: 'My First Post', bod: 'Hello World!' }. If we don't write resolvers for any of the fields on the Post type, we can still request the post:
query {
post {
id
title
body
}
}
and our response will be
{
"data": {
"post" {
"id": null,
"title": "My First Post",
"body": null,
}
}
}
The title field was resolved even though we didn't provide a resolver for it because the default resolver did the heavy lifting -- it saw there was a property named title on the Object the parent field (in this case post) resolved to and so it just resolved to that property's value. The id field resolved to null because the object we returned in our post resolver did not have an id property. The body field also resolved to null because of a typo -- we have a property called bod instead of body!
Pro tip: If bod is not a typo but what an API or database actually returns, we can always write a resolver for the body field to match our schema. For example: (parent) => parent.bod
One important thing to keep in mind is that in JavaScript, almost everything is an Object. So if the post field resolves to a String or a Number, the default resolver for each of the fields on the Post type will still try to find an appropriately named property on the parent object, inevitably fail and return null. If a field has an object type but you return something other than object in its resolver (like a String or an Array), you will not see any error about the type mismatch but the child fields for that field will inevitably resolve to null.
Common Scenario #1: Wrapped Responses
If we're writing the resolver for the post query, we might fetch our code from some other endpoint, like this:
function post (root, args) {
// axios
return axios.get(`http://SOME_URL/posts/${args.id}`)
.then(res => res.data);
// fetch
return fetch(`http://SOME_URL/posts/${args.id}`)
.then(res => res.json());
// request-promise-native
return request({
uri: `http://SOME_URL/posts/${args.id}`,
json: true
});
}
The post field has the type Post, so our resolver should return an object with properties like id, title and body. If this is what our API returns, we're all set. However, it's common for the response to actually be an object which contains additional metadata. So the object we actually get back from the endpoint might look something like this:
{
"status": 200,
"result": {
"id": 1,
"title": "My First Post",
"body": "Hello world!"
},
}
In this case, we can't just return the response as-is and expect the default resolver to work correctly, since the object we're returning doesn't have the id , title and body properties we need. Our resolver isn't needs to do something like:
function post (root, args) {
// axios
return axios.get(`http://SOME_URL/posts/${args.id}`)
.then(res => res.data.result);
// fetch
return fetch(`http://SOME_URL/posts/${args.id}`)
.then(res => res.json())
.then(data => data.result);
// request-promise-native
return request({
uri: `http://SOME_URL/posts/${args.id}`,
json: true
})
.then(res => res.result);
}
Note: The above example fetches data from another endpoint; however, this sort of wrapped response is also very common when using a database driver directly (as opposed to using an ORM)! For example, if you're using node-postgres, you'll get a Result object that includes properties like rows, fields, rowCount and command. You'll need to extract the appropriate data from this response before returning it inside your resolver.
Common Scenario #2: Array Instead of Object
What if we fetch a post from the database, our resolver might look something like this:
function post(root, args, context) {
return context.Post.find({ where: { id: args.id } })
}
where Post is some model we're injecting through the context. If we're using sequelize, we might call findAll. mongoose and typeorm have find. What these methods have in common is that while they allow us to specify a WHERE condition, the Promises they return still resolve to an array instead of a single object. While there's probably only one post in your database with a particular ID, it's still wrapped in an array when you call one of these methods. Because an Array is still an Object, GraphQL will not resolve the post field as null. But it will resolve all of the child fields as null because it won't be able to find the appropriately named properties on the array.
You can easily fix this scenario by just grabbing the first item in the array and returning that in your resolver:
function post(root, args, context) {
return context.Post.find({ where: { id: args.id } })
.then(posts => posts[0])
}
If you're fetching data from another API, this is frequently the only option. On the other hand, if you're using an ORM, there's often a different method that you can use (like findOne) that will explicitly return only a single row from the DB (or null if it doesn't exist).
function post(root, args, context) {
return context.Post.findOne({ where: { id: args.id } })
}
A special note on INSERT and UPDATE calls: We often expect methods that insert or update a row or model instance to return the inserted or updated row. Often they do, but some methods don't. For example, sequelize's upsert method resolves to a boolean, or tuple of the the upserted record and a boolean (if the returning option is set to true). mongoose's findOneAndUpdate resolves to an object with a value property that contains the modified row. Consult your ORM's documentation and parse the result appropriately before returning it inside your resolver.
Common Scenario #3: Object Instead of Array
In our schema, the posts field's type is a List of Posts, which means its resolver needs to return an Array of objects (or a Promise that resolves to one). We might fetch the posts like this:
function posts (root, args) {
return fetch('http://SOME_URL/posts')
.then(res => res.json())
}
However, the actual response from our API might be an object that wraps the the array of posts:
{
"count": 10,
"next": "http://SOME_URL/posts/?page=2",
"previous": null,
"results": [
{
"id": 1,
"title": "My First Post",
"body" "Hello World!"
},
...
]
}
We can't return this object in our resolver because GraphQL is expecting an Array. If we do, the field will resolve to null and we'll see an error included in our response like:
Expected Iterable, but did not find one for field Query.posts.
Unlike the two scenarios above, in this case GraphQL is able to explicitly check the type of the value we return in our resolver and will throw if it's not an Iterable like an Array.
Like we discussed in the first scenario, in order to fix this error, we have to transform the response into the appropriate shape, for example:
function posts (root, args) {
return fetch('http://SOME_URL/posts')
.then(res => res.json())
.then(data => data.results)
}
Not Using Promises Correctly
GraphQL.js makes use of the Promise API under the hood. As such, a resolver can return some value (like { id: 1, title: 'Hello!' }) or it can return a Promise that will resolve to that value. For fields that have a List type, you may also return an array of Promises. If a Promise rejects, that field will return null and the appropriate error will be added to the errors array in the response. If a field has an Object type, the value the Promise resolves to is what will be passed down as the parent value to the resolvers of any child fields.
A Promise is an "object represents the eventual completion (or failure) of an asynchronous operation, and its resulting value." The next few scenarios outline some common pitfalls encountered when dealing with Promises inside resolvers. However, if you're not familiar with Promises and the newer async/await syntax, it's highly recommended you spend some time reading up on the fundamentals.
Note: the next few examples refer to a getPost function. The implementation details of this function are not important -- it's just a function that returns a Promise, which will resolve to a post object.
Common Scenario #4: Not Returning a Value
A working resolver for the post field might looks like this:
function post(root, args) {
return getPost(args.id)
}
getPosts returns a Promise and we're returning that Promise. Whatever that Promise resolves to will become the value our field resolves to. Looking good!
But what happens if we do this:
function post(root, args) {
getPost(args.id)
}
We're still creating a Promise that will resolve to a post. However, we're not returning the Promise, so GraphQL is not aware of it and it will not wait for it to resolve. In JavaScript functions without an explicit return statement implicitly return undefined. So our function creates a Promise and then immediately returns undefined, causing GraphQL to return null for the field.
If the Promise returned by getPost rejects, we won't see any error listed in our response either -- because we didn't return the Promise, the underlying code doesn't care about whether it resolves or rejects. In fact, if the Promise rejects, you'll see an
UnhandledPromiseRejectionWarning in your server console.
Fixing this issue is simple -- just add the return.
Common Scenario #5: Not chaining Promises correctly
You decide to log the result of your call to getPost, so you change your resolver to look something like this:
function post(root, args) {
return getPost(args.id)
.then(post => {
console.log(post)
})
}
When you run your query, you see the result logged in your console, but GraphQL resolves the field to null. Why?
When we call then on a Promise, we're effectively taking the value the Promise resolved to and returning a new Promise. You can think of it kind of like Array.map except for Promises. then can return a value, or another Promise. In either case, what's returned inside of then is "chained" onto the original Promise. Multiple Promises can be chained together like this by using multiple thens. Each Promise in the chain is resolved in sequence, and the final value is what's effectively resolved as the value of the original Promise.
In our example above, we returned nothing inside of the then, so the Promise resolved to undefined, which GraphQL converted to a null. To fix this, we have to return the posts:
function post(root, args) {
return getPost(args.id)
.then(post => {
console.log(post)
return post // <----
})
}
If you have multiple Promises you need to resolve inside your resolver, you have to chain them correctly by using then and returning the correct value. For example, if we need to call two other asynchronous functions (getFoo and getBar) before we can call getPost, we can do:
function post(root, args) {
return getFoo()
.then(foo => {
// Do something with foo
return getBar() // return next Promise in the chain
})
.then(bar => {
// Do something with bar
return getPost(args.id) // return next Promise in the chain
})
Pro tip: If you're struggling with correctly chaining Promises, you may find async/await syntax to be cleaner and easier to work with.
Common Scenario #6
Before Promises, the standard way to handle asynchronous code was to use callbacks, or functions that would be called once the asynchronous work was completed. We might, for example, call mongoose's findOne method like this:
function post(root, args) {
return Post.findOne({ where: { id: args.id } }, function (err, post) {
return post
})
The problem here is two-fold. One, a value that's returned inside a callback isn't used for anything (i.e. it's not passed to the underlying code in any way). Two, when we use a callback, Post.findOne doesn't return a Promise; it just returns undefined. In this example, our callback will be called, and if we log the value of post we'll see whatever was returned from the database. However, because we didn't use a Promise, GraphQL doesn't wait for this callback to complete -- it takes the return value (undefined) and uses that.
Most more popular libraries, including mongoose support Promises out of the box. Those that don't frequently have complimentary "wrapper" libraries that add this functionality. When working with GraphQL resolvers, you should avoid using methods that utilize a callback, and instead use ones that return Promises.
Pro tip: Libraries that support both callbacks and Promises frequently overload their functions in such a way that if a callback is not provided, the function will return a Promise. Check the library's documentation for details.
If you absolutely have to use a callback, you can also wrap the callback in a Promise:
function post(root, args) {
return new Promise((resolve, reject) => {
Post.findOne({ where: { id: args.id } }, function (err, post) {
if (err) {
reject(err)
} else {
resolve(post)
}
})
})
I had the same issue on Nest.js.
If you like to solve the issue. You can add {nullable: true} option to your #Query decorator.
Here's an example.
#Resolver(of => Team)
export class TeamResolver {
constructor(
private readonly teamService: TeamService,
private readonly memberService: MemberService,
) {}
#Query(returns => Team, { name: 'team', nullable: true })
#UseGuards(GqlAuthGuard)
async get(#Args('id') id: string) {
return this.teamService.findOne(id);
}
}
Then, you can return null object for query.
Coming from Flutter here.
I couldn't find any flutter related solution to this so since my search always brought me here, lemme just add it here.
The exact error was:
Failure performing sync query to AppSync:
[GraphQLResponse.Error{message='Cannot return null for non-nullable
type: 'AWSTimestamp' within parent
So, in my schema (on the AppSync console) I had this:
type TypeName {
id: ID!
...
_version: Int!
_deleted: Boolean
_lastChangedAt: AWSTimestamp!
createdAt: AWSDateTime!
updatedAt: AWSDateTime!
}
I got the error from the field _lastChangedAt as AWSTimestamp couldn't be null.
All I had to do was remove the null-check (!) from the field and it was resolved.
Now, I don't know the implications of this in the long run but I'll update this answer if necessary.
EDIT: The implication of this as I have found out is anything I do, amplify.push that change is reversed. Just go back to your appsync console and change it again while you test. So this isn't a sustainable solution but chatter I've picked up online suggests improvements are coming to amplify flutter very soon.
#Thomas Hennes got it spot on for me
The title field was resolved even though we didn't provide a resolver for it because the default resolver did the heavy lifting -- it saw there was a property named title on the Object the parent field (in this case post) resolved to and so it just resolved to that property's value. The id field resolved to null because the object we returned in our post resolver did not have an id property. The body field also resolved to null because of a typo -- we have a property called bod instead of body!
Pro tip: If bod is not a typo but what an API or database actually returns, we can always write a resolver for the body field to match our schema. For example: (parent) => parent.bod
One important thing to keep in mind is that in JavaScript, almost everything is an Object. So if the post field resolves to a String or a Number, the default resolver for each of the fields on the Post type will still try to find an appropriately named property on the parent object, inevitably fail and return null. If a field has an object type but you return something other than object in its resolver (like a String or an Array), you will not see any error about the type mismatch but the child fields for that field will inevitably resolve to null.
In case anyone has used apollo-server-express and getting null value.
// This will return values, as you expect.
const typeDefs = require('./schema');
const resolvers = require('./resolver');
const server = new ApolloServer({typeDefs,resolvers});
// This will return null, since ApolloServer constructor is not using correct properties.
const withDifferentVarNameSchema = require('./schema');
const withDifferentVarNameResolver= require('./resolver');
const server = new ApolloServer({withDifferentVarNameSchema,withDifferentVarNameResolver});
Note: While creating an instance of Apolloserver pass the typeDefs and resolvers var name only.
If none of the above helped, and you have a global interceptor that envelopes all the responses for example inside a "data" field, you must disable this for graphql other wise graphql resolvers convert to null.
This is what I did to the interceptor on my case:
intercept(
context: ExecutionContext,
next: CallHandler,
): Observable<Response<T>> {
if (context['contextType'] === 'graphql') return next.handle();
return next
.handle()
.pipe(map(data => {
return {
data: isObject(data) ? this.transformResponse(data) : data
};
}));
}
I have just switched over from studying Java to studying Javascript and I am trying to learn React and Redux right now. I am having some confusion with how some objects seem to be created in this tutorial I have been following on YouTube. This tut has so far just covered logging in and signing into a webpage.
api.js
import axios from "axios";
export default {
user: {
login: credentials =>
axios.post("/api/auth", { credentials }).then(res => res.data.user),
signup: user =>
axios.post("/api/users", { user }).then(res => res.data.user),
confirm: token =>
axios.post("/api/auth/confirmation", { token }).then(res => res.data.user)
}
};
This is what I am understanding from this code currently:
axios is imported so that various HTTP requests can be made. A user object is created that contains an array of 3 objects (functions?) : login, signup and confirm. In login object, an arrow function is used to pass credentials as the parameter into the axios object's post function. A promise is then called where the response data is passed into ??? which returns a res.data.user object.
I don't understand what the res.data.user object is, why is it described in such form with the dot separation instead of just something like responseDataObject?
This next piece of code is the 'action' part of the app (Redux) where the api.js is imported. Here 2 of the functions are exported into a new function which is called depending on the state of the user.... I don't think the other parts are relevant to talk about because I understand that programming logic. What I don't understand is how and why the res.data.object is returned like that. Where is the data part coming from? Is that arbitrarily described?
I am clearing missing something here, I've been watching some videos to try to understand what's going on but I think it might be a simple reason best described here.
There are a few terminologies you are using or understanding incorrectly. I think it is important to understand them before dive too deep into React.
First, Object:
An object has key/value pairs.
{
fruit: "apple"
}
that contains an array of 3 objects (functions?)
This would be incorrect. Since array's syntax is []. What you were describing is element or member or key.
Next part is about the promise in Javascript. You have this code. axios.post("/api/auth", { credentials }).then(res => res.data.user), This is basically saying once you call the api with that url, some data will come back(we stored in res). But the res is an object in this case.
If you console log res, you will get an object like this:
{
...
key1: "something",
key2: "something else",
data: {
...
user: { //some info about the user}
...
},
...
}
What you want is the data inside of res, more specifically you want the user's value. So to access it, you want to use res.data.user.
Hopefully, this answers some of your questions, but there is a lot to talk about. You should read more on js's object.
https://www.w3schools.com/js/js_objects.asp
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise
Welcome to JS world :)
A user object is created that contains an array of 3 objects
(functions?)
Yep it's just 3 simple functions
A promise is then called where the response data is passed into ???
which returns a res.data.user object.
Promise is resolved (then function called) when server response status 2** and inside then res is just simple object witch is come from server (status, headers, response body), here is docs describing what res contains: https://www.npmjs.com/package/axios#response-schema
So inside res.data - client assumed that server responds with user object which contains some user data (example server returns json {user: {id: 1, name: 'Hary'}})
I don't understand what the res.data.user object is, why is it
described in such form with the dot separation instead of just
something like responseDataObject?
You just accessing object properties (example res = {data: {user: {id: 1, name: 'Hary'}}})
So this code .then(res => res.data.user) just an simple helper to return user and not whole response from server, here how you can use it user.login({login: 'cool_user', password: 'qwerty'}).then(user => console.log(user.id)) so if I assumed that sever retunrs this data you got into console user id after success login
One thing not covered in the other posts is this syntax:
export default {
// ...
};
This exports an object from the api.js file. This object is not assigned to a variable or given a name here. Instead, you do that when you import:
import api from 'api.js';
Now in the file with this import, the name api refers to the object exported from api.js. So you can do things like api.user.login(credentials) to call one of the functions defined iniside this object.
Hi I'm trying to update my database with function that returns a number
$scope.sum = function()
{
return $scope.inp + $scope.points;
};
this function will update the record in object points, column name and id 1:
$scope.addPoint = function() {
PointService.addPoint($scope.sum, 1)
.then(function(result) {
$scope.inp = 0;
getMyPoints();
});
}
addPoint = function(id,points)
{
return $http.put(getUrlForId(1),points,name);
}
the error is: Error details: Cannot convert type 'int' to 'System.Collections.Generic.Dictionary'
the data type of the field is Float.
Any idea what is wrong with the code?
you are passing function reference to PointService.addPointer(),
use this:
$scope.addPoint = function() {
PointService.addPoint($scope.sum(), 1) // NOT PointService.addPoint($scope.sum, 1)
.then(function(result) {
$scope.inp = 0;
getMyPoints();
});
}
this will execute your function and pass the output (id parameter) to addPoint function, further, for more safe side, you can return Number from $scope.sum() i.e.
$scope.sum = function()
{
return Number($scope.inp + $scope.points);
};
This looks like an issue with how you're contacting Backand. You use the following code to send your points over:
addPoint = function(id,points)
{
return $http.put(getUrlForId(1),points,name);
}
This is an older version of calling the Backand API that is manually constructing a PUT request, and putting "points" and "name" as the "Data" and "config" parameters to $http. With an object update via PUT, you'll need to provide the updates as an object. So if you wanted to update the points and the name of the object (and I'm doing some assuming based upon what I can tell from the code snippet above), you'd need to encapsulate these properties in an object that has the following general format:
{
"field_name_1":"new value_1",
"field_name_2":"new value_2",
etc ...
}
This should then be sent as the body of the request. So, for your code, change it to the following and see if this helps:
addPoint = function(id,points)
{
return $http.put(getUrlForId(1),{points: points, name: name});
}
To give more info on why you're seeing this particular error, Backand is depending on this JSON format in the body. Our platform should definitely do more validation (and I'll create a ticket for the devs to handle non-conforming input more gracefully), but at the moment we simply take the body of the request, convert it to a dictionary object, then begin the requested operation. As your code above sends only "1.0" as the body, this fails the conversion into a dictionary, causing the stack exception and the issue you are seeing.
As a note, we offer a new SDK that encapsulates these HTTP methods, performing the authentication header generation and HTTP messaging for you, providing promises to handle responses. You can find it on our Github page at https://github.com/backand/vanilla-sdk. To make the same call using the new SDK, the code would resemble the following:
backand.object.update("your object name", 1, {name: name, points: points})
.then(function(response){
console.log(response.data);
});
Hi I have this model :
window.shop = Backbone.Model.extend({
initialize: function () {
console.log('initializing shop');
},
urlRoot: "shopData.json",
});
and then i go :
var myShop = new shop();
myShop.fetch({
success: function (model, resp){
console.log(resp);
},
error: function (model, resp){
console.log("error retrieving model");
}}, {wait: true});
now I'm always getting the error message - never reaching success :-(
thanks for any help.
Edit 1:
As per your comment the server is sending the proper response but Backbone is still calling the error function. Add the following line at the beginning of the error callback:
error: function (model, resp){
console.log('error arguments: ', arguments);
console.log("error retrieving model");
}
The first line should print an array of objects. The first element in the array should the jqXhr object, the second should be a string representation of the error. If you click on the first object, the dev tools will let you inspect its properties. Read up on the properties of the object here http://api.jquery.com/jQuery.ajax/#jqXHR.
Using that information you can verify if the jQuery is receiving an error from the server.
If there is no server side error, then check the value of the responseText property. That holds the string data returned from the server. $.ajax will try to parse that data into JSON. Most likely the parsing is throwing an error and the error handler is being raised instead.
Copy the response text and paste it into http://jsonlint.com/. Verify that the response sent from the server is valid JSON. Do update your question with the output of the console.log statement and the responseText property of the jqxhr object.
-x-x-x-
You seem to be using the model independently. As the per the documentation, http://backbonejs.org/#Model-url,
Generates URLs of the form: "/[urlRoot]/id"
That means, you are making a request to shopData.json/id. Also, you haven't specified the id.
Insert a console.log(myShop.url()) before the myShop.fetch(). Let us know whats the output. Also, possibly share the details of the ajax request as seen in Firebug or Chrome Dev Tools. I am interested in two things, the request url and the response returned by the server. (http://getfirebug.com/network)
I have a mode that saves data to a codeigniter function the codeigniter function returns valid JSON data back if it has an error how do i get the error details that the server returns when using save(). I have the following code that doesn't work
this.newproject.save({
'Objective':Objective,
"Planner":Planner,
"NISupervisor":NISupervisor,
"SiteIDs":SiteIDs,
"Status":Status ,
"StartDate":StartDate,
"EndDate":EndDate,
"Details":Details,
"PrjTitle":PrjTitle
},{
success:function(model,response){
console.log(response);
}
},{
error:function(){
alert("wrong");
}
});
Success doesn't work at all
The 2nd option to save is an object with 2 properties, success and error. I'm assuming that you mean that "error" doesn't work at all, and success works fine, based on your actual question text.
this.newproject.save({
'Objective':Objective,
"Planner":Planner,
"NISupervisor":NISupervisor,
"SiteIDs":SiteIDs,
"Status":Status ,
"StartDate":StartDate,
"EndDate":EndDate,
"Details":Details,
"PrjTitle":PrjTitle
},{
success:function(model,response){console.log(response);},
error:function(model,response){console.log(response);}
});
The error callback also passes model and response, so the response argument is what you're probably looking for.
The problem with your code is that you've got three hash arguments. The save method accepts attrs and options as its two arguments. As such, your code should look similar to this:
var attrs = {
"Objective":Objective,
"Planner":Planner,
"NISupervisor":NISupervisor,
"SiteIDs":SiteIDs,
"Status":Status ,
"StartDate":StartDate,
"EndDate":EndDate,
"Details":Details,
"PrjTitle":PrjTitle
};
this.newproject.save(attrs, {
success: function(model, response) {
console.log(response);
},
error: function(model, response) {
alert('wrong');
}
});
So your call would not have been able to attach the error function. The above example should work for you since it combines the success and error functions in the second hash argument.