Graphql returning Cannot return null for non-nullable field Query.getDate. As I am new to graphql I want to know is my approach is wrong or my code? - aws-lambda

Question

I have created resolver, schema and handler which will fetch some record from dynamoDB. Now when I perform query then I am getting "Cannot return null for non-nullable field Query.getDate" error. I would like to know whether my approach is wrong or there is any change required in code.
My code : https://gist.github.com/vivek-chavan/95e7450ff73c8382a48fb5e6a5b96025
Input to lambda :
{
"query": "query getDate {\r\n getDate(id: \"0f92fa40-8036-11e8-b106-952d7c9eb822#eu-west-1:ba1c96e7-92ff-4d63-879a-93d5e397b18a\") {\r\n id\r\n transaction_date\r\n }\r\n }"
}
Response :
{
"errors": [
{
"message": "Cannot return null for non-nullable field Query.getDate.",
"locations": [
{
"line": 2,
"column": 7
}
],
"path": [
"getDate"
]
}
],
"data": null
}
Logs of lambda function :
[ { Error: Cannot return null for non-nullable field Query.getDate.
at completeValue (/var/task/node_modules/graphql/execution/execute.js:568:13)
at completeValueCatchingError (/var/task/node_modules/graphql/execution/execute.js:503:19)
at resolveField (/var/task/node_modules/graphql/execution/execute.js:447:10)
at executeFields (/var/task/node_modules/graphql/execution/execute.js:293:18)
at executeOperation (/var/task/node_modules/graphql/execution/execute.js:237:122)
at executeImpl (/var/task/node_modules/graphql/execution/execute.js:85:14)
at execute (/var/task/node_modules/graphql/execution/execute.js:62:229)
at graphqlImpl (/var/task/node_modules/graphql/graphql.js:86:31)
at /var/task/node_modules/graphql/graphql.js:32:223
at graphql (/var/task/node_modules/graphql/graphql.js:30:10)
message: 'Cannot return null for non-nullable field Query.getDate.',
locations: [Object],
path: [Object] } ],
data: null }
2019-02-25T10:07:16.340Z 9f75d1ea-2659-490b-ba59-5289a5d18d73 { Item:
{ model: 'g5',
transaction_date: '2018-07-05T09:30:31.391Z',
id: '0f92fa40-8036-11e8-b106-952d7c9eb822#eu-west-1:ba1c96e7-92ff-4d63-879a-93d5e397b18a',
make: 'moto' } }
Thanks in advance!

Answer 1

This is your code:
const data = {
getDate(args) {
var params = {
TableName: 'delete_this',
Key: {
"id": args.id
}
};
client.get(params, function(err,data){
if(err){
console.log('error occured '+err)
}else{
console.log(data)
}
});
},
};
const resolvers = {
Query: {
getDate: (root, args) => data.getDate(args),
},
};
You're seeing that error because getDate is a a Non-Null field in your schema, but it is resolving to null. Your resolver needs to return either a value of the appropriate type, or a Promise that will resolve to that value. If you change data like this
const data = {
getDate(args) {
return {
id: 'someString',
transaction_date: 'someString',
}
}
}
you'll see the error go away. Of course, your goal is to return data from your database, so we need to add that code back in. However, your existing code utilizes a callback. Anything you do inside the callback is irrelevant because it's ran after your resolver function returns. So we need to use a Promise instead.
While you can wrap a callback with Promise, that shouldn't be necessary with aws-sdk since newer versions support Promises. Something like this should be sufficient:
const data = {
getDate(args) {
const params = //...
// must return the resulting Promise here
return client.get(params).promise().then(result => {
return {
// id and transaction_date based on result
}
})
}
}
Or using async/await syntax:
const data = {
async getDate(args) {
const params = //...
const result = await client.get(params).promise()
return {
// id and transaction_date based on result
}
}
}