Graphql Cant Return Array

Question

I am using Apollo-Server and trying to create a REST query against the IEX REST API which returns back data that looks like this:

{
  "symbol": "AAPL",
  "companyName": "Apple Inc.",
  "exchange": "Nasdaq Global Select",
  "industry": "Computer Hardware",
  "website": "http://www.apple.com",
  "description": "Apple Inc is an American multinational technology company. It designs, manufactures, and markets mobile communication and media devices, personal computers, and portable digital music players.",
  "CEO": "Timothy D. Cook",
  "issueType": "cs",
  "sector": "Technology",
  "tags": [
      "Technology",
      "Consumer Electronics",
      "Computer Hardware"
  ]
}

I am using datasources. My typeDefs and resolvers look something like this:

const typeDefs = gql`
    type Query{
        stock(symbol:String): Stock
    }

    type Stock {
        companyName: String
        exchange: String
        industry: String
        tags: String!
    }
`;
const resolvers = {
    Query:{
        stock: async(root, {symbol}, {dataSources}) =>{
            return dataSources.myApi.getSomeData(symbol)
        }
    }
};

The Datasource file looks like this:

class MyApiextends RESTDataSource{
    constructor(){
        super();
        this.baseURL = 'https://api.iextrading.com/1.0';
    }

    async getSomeData(symbol){
        return this.get(`/stock/${symbol}/company`)
    }
}

module.exports = MyApi

I can run a query and get data back, but it is not formatting in an array and is throwing an error when I run a query like so:

query{
  stock(symbol:"aapl"){
    tags
  }
}

Error:

{
  "data": {
    "stock": null
  },
  "errors": [
    {
      "message": "String cannot represent value: [\"Technology\", \"Consumer Electronics\", \"Computer Hardware\"]",
      "locations": [
        {
          "line": 3,
          "column": 5
        }
      ],
      "path": [
        "stock",
        "tags"
      ],
      "extensions": {
        "code": "INTERNAL_SERVER_ERROR",
        "exception": {
          "stacktrace": [
            "TypeError: String cannot represent value: [\"Technology\", \"Consumer Electronics\", \"Computer Hardware\"]",

The data I am expecting (technology, consumer electronics, and computer hardware) are correct, but not returning in an array. I tried to make a new type for tags, and set the it with a tag property, but the value just returns null.

I am very new to graphql, so any feedback is appreciated!

Welcome to SO! It would be helpful to see your datasource code as well. Can you update your question to include that as well? — Daniel Rearden
– Daniel Rearden, Commented Sep 20, 2018 at 12:08

Daniel Rearden · Accepted Answer · 2018-09-20 13:01:21Z

5

Inside your type definition for Stock, you're defining the type for the tags field as String!:

tags: String!

That tells GraphQL to expect a String value that will not be null. The actual data being returned by the REST endpoint, however, is not a String -- it's an array of Strings. So your definition should minimally look like this:

tags: [String]

If you want GraphQL to throw if the tags value is null, add an exclamation point to the end to make it non-nullable:

tags: [String]!

If you want GraphQL to throw if any of the values inside the array are null, add an exclamation point inside the brackets. You can also combine the two:

tags: [String!]!

answered Sep 20, 2018 at 13:01

Daniel Rearden

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