How can we add a new field to an existing schema using graphql-tools

[Ramakant2021]

I am trying to add a new field to an existing schema using graphql-tools. I am trying using appendObjectFields() without success as below. I am getting error "Cannot query field "newField" on type "Product"

transformSchema(schema: GraphQLSchema) {
typeName: string = "String";
fieldName: string = "newField";
schemaTypename: string = "Product";

const QueryType = schema.getQueryType();
const queryConfig = QueryType.toConfig();

const nestedQuery = new GraphQLObjectType({
  ...queryConfig,
  name: this.typeName,
});
 
const newRootFieldConfigMap: GraphQLFieldConfigMap<any, any> = {
  [this.fieldName]: {
    type: new GraphQLNonNull(nestedQuery),
    resolve: (parent, args, context, info) => {
      if (this.resolver != null) {
        console.log("Resolver is not null");
        return "10";
      }
      return "11";
    },
  },
};

schema = appendObjectFields(schema, this.schemaTypename, newRootFieldConfigMap);
return schema;

}

[ardatan]

You can use mergeSchemas from @graphql-tools/merge
https://www.graphql-tools.com/docs/schema-merging

mergeSchemas({
  schemas: [schema],
  typeDefs: ``, // Additional typeDefs here
  resolvers: {} // Additional resolvers here
})

[Ramakant2021]

Thanks for the answer. I have tried with mergeSchemas from @graphql-tools/merge earlier but it gives me following error "Cannot query field "foo" on type "Product". Not sure where I am going wrong. Can you please advice.

import { mergeSchemas } from "@graphql-tools/merge";

export class AddField {
  
  transformSchema(schema: GraphQLSchema) {
      const mergedSchema = mergeSchemas({
      schemas: [
        schema
      ],
      typeDefs: `
        type Product {
          foo: String
        }
      `,
      resolvers: {
        Product: {
          foo: () => "FOO",
        }
      }
    });
    
   return mergedSchema; 
}
}

**Error**
{
  "errors": [
    {
      "message": "Cannot query field \"foo\" on type \"Product\".",
      "path": [
        "findProducts"
      ],
      "extensions": {
        "code": "GRAPHQL_VALIDATION_FAILED",
        "exception": {
          "stacktrace": [
            "GraphQLError: Cannot query field \"foo\" on type \"Product\".",
            "    at Object.relocatedError (d:\\BFF\\designer-bff-new\\node_modules\\@graphql-tools\\utils\\index.cjs.js:3953:12)",
            "    at mergeDataAndErrors (d:\\BFF\\designer-bff-new\\node_modules\\@graphql-tools\\delegate\\index.cjs.js:1400:34)",
            "    at checkResultAndHandleErrors (d:\\BFF\\designer-bff-new\\node_modules\\@graphql-tools\\delegate\\index.cjs.js:1389:38)",
            "    at CheckResultAndHandleErrors.transformResult (d:\\BFF\\designer-bff-new\\node_modules\\@graphql-tools\\delegate\\index.cjs.js:1385:16)",
            "    at d:\\BFF\\designer-bff-new\\node_modules\\@graphql-tools\\delegate\\index.cjs.js:1572:40",
            "    at Array.reduceRight (<anonymous>)",
            "    at Transformer.transformResult (d:\\BFF\\designer-bff-new\\node_modules\\@graphql-tools\\delegate\\index.cjs.js:1571:37)",
            "    at d:\\BFF\\designer-bff-new\\node_modules\\@graphql-tools\\delegate\\index.cjs.js:1657:48",
            "    at processTicksAndRejections (internal/process/task_queues.js:95:5)",
            "    at async d:\\BFF\\designer-bff-new\\node_modules\\@graphql-mesh\\runtime\\index.cjs.js:96:32"
          ]
        }
      }
    }
  ],
  "data": {
    "findProducts": null
  }
}
``

[ardatan]

Why do you create transform? Just use the schema returned by mergeSchemas

[Ramakant2021]

I need transformSchema() as I am trying to create a new custom Transform. I found the issue with the code. Its resolved now. Thanks for your help