Unable to merge GraphQL type ... undefined is not iterable (for a duplicate type)

[kumar303]

Using [email protected], I was trying to call something like:

import {mergeTypes} from 'merge-graphql-schemas';

(async () => {
    mergeTypes(
      await Promise.all([
        fs.readFile('schema1.graphql'),
        fs.readFile('schema2.graphql'),
      ]),
    );
})();

I got an error like:

Error: Unable to merge GraphQL type "MyType": undefined is not iterable (cannot read property Symbol(Symbol.iterator))
    at mergeType (/.../app/node_modules/@graphql-toolkit/schema-merging/index.cjs.js:675:19)
    at /.../app/node_modules/@graphql-toolkit/schema-merging/index.cjs.js:717:30
    at Array.reduce (<anonymous>)
    at mergeGraphQLNodes (/.../app/node_modules/@graphql-toolkit/schema-merging/index.cjs.js:706:18)
    at mergeGraphQLTypes (/.../app/node_modules/@graphql-toolkit/schema-merging/index.cjs.js:856:25)
    at Object.mergeTypeDefs (/.../app/node_modules/@graphql-toolkit/schema-merging/index.cjs.js:755:22)
    at mergeTypes (/.../app/node_modules/merge-graphql-schemas/dist/index.cjs.js:24:26)
    ...

I was trying to introduce type MyType {} in schema1.graphql but that exact type already existed in schema2.graphql.

This error message should be more informative. RIP my last hour.

[ardatan]

merge-graphql-schemas has been deprecated as you can see in https://github.com/Urigo/merge-graphql-schemas/blob/master/README.md We recommend you to start using GraphQL Tools instead; https://www.graphql-tools.com/docs/migration-from-merge-graphql-schemas/

[kumar303]

Since I have the solution, I just wanted to post it here so that someone else could search and find it. I was trying to search for this error and not finding anything.

Ultimately, I'd hope the newer lib has a better error message but I'm not able to migrate my app at this time.

[ArtemKislov]

@kumar303

Since I have the solution, I just wanted to post it here so that someone else could search and find it. I was trying to search for this error and not finding anything.

You have just saved me an hour :) thanks for the explanation!