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Extend the schema with custom resolvers

Combining multiple Sources explains how additionalResolvers can shape and augment the unified schema with custom resolvers.

Alternatively, using the additionalResolvers config allows you to upload a custom resolver as a JavaScript file to the Mesh.

Programmatic additionalResolvers

In this example, we will use additionalResolvers to apply a set of discounts to products in Adobe Commerce. The following example uses two handlers:

  • The Venia handler is a publicly available Adobe Commerce GraphQL endpoint for the Venia sample storefront.

  • The DiscountsAPI handler points to a .json file that contains key-value pairs of sample item names and their corresponding discount percentages.

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{
  "meshConfig": {
    "sources": [
      {
        "name": "Venia",
        "handler": {
          "graphql": {
            "endpoint": "https://venia.magento.com/graphql"
          }
        }
      },
      {
        "name": "DiscountsAPI",
        "handler": {
          "JsonSchema": {
            "baseUrl": "https://raw.githubusercontent.com/AdobeDocs/graphql-mesh-gateway/main/src/pages/_examples/discounts-api.json",
            "operations": [
              {
                "type": "Query",
                "field": "discounts",
                "path": "/",
                "method": "GET",
                "responseSample": "https://raw.githubusercontent.com/AdobeDocs/graphql-mesh-gateway/main/src/pages/_examples/discounts-api.json"
              }
            ]
          }
        }
      }
    ],
    "additionalResolvers": [
      "./additional-resolvers.js"
    ],
    "files": [
      {
        "path": "./additional-resolvers.js",
        "content": "\r\nmodule.exports = {\r\n\tresolvers: {\r\n\t\tConfigurableProduct: {\r\n\t\t\tspecial_price: {\r\n\t\t\t\tselectionSet: \"{ name price_range { maximum_price { final_price { value } } } }\",\r\n\t\t\t\tresolve: (root, args, context, info) => {\r\n\t\t\t\t\tlet max = 0;\r\n\r\n\t\t\t\t\ttry {\r\n\t\t\t\t\t\tmax = root.price_range.maximum_price.final_price.value;\r\n\t\t\t\t\t} catch (e) {\r\n\t\t\t\t\t\t// ignore\r\n\t\t\t\t\t}\r\n\r\n\t\t\t\t\treturn context.DiscountsAPI.Query.discounts(\r\n\t\t\t\t\t\t{ root, args, context, info, selectionSet: \"{ name discount }\" }\r\n\t\t\t\t\t)\r\n\t\t\t\t\t\t.then((response) => {\r\n\t\t\t\t\t\t\tconst discountConfig = response.find((discount) => discount.name === root.name);\r\n\r\n\t\t\t\t\t\t\tif (discountConfig) {\r\n\t\t\t\t\t\t\t\treturn max * ((100 - discountConfig.discount) / 100);\r\n\t\t\t\t\t\t\t} else {\r\n\t\t\t\t\t\t\t\treturn max\r\n\t\t\t\t\t\t\t}\r\n\t\t\t\t\t\t})\r\n\t\t\t\t\t\t.catch(() => {\r\n\t\t\t\t\t\t\treturn null;\r\n\t\t\t\t\t\t});\r\n\t\t\t\t},\r\n\t\t\t},\r\n\t\t},\r\n\t},\r\n};\r\n"
      }
    ]
  }
}

The previous example contains a files object that contains the following javascript:

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module.exports = {
    resolvers: {
        ConfigurableProduct: {
            special_price: {
                selectionSet: '{ name price_range { maximum_price { final_price { value } } } }',
                resolve: (root, args, context, info) => {
                    let max = 0;


                    try {
                        max = root.price_range.maximum_price.final_price.value;
                    } catch (e) {
                        // ignore
                    }


                    return context.DiscountsAPI.Query.discounts({
                            root,
                            args,
                            context,
                            info,
                            selectionSet: '{ name discount }',
                        })
                        .then(response => {
                            let discount = 0;
                            const discountConfig = response.find(discount => discount.name === root.name);


                            if (discountConfig) {
                                discount = discountConfig.discount;
                            }


                            return max * ((100 - discount) / 100);
                        })
                        .catch(() => {
                            return null;
                        });
                },
            },
        },
    },
};

This javascript file targets the special_price field on ConfigurableProduct that uses the maximum_price for a product and then applies the discount listed for that product in the discountsapi.json file. The following arguments define how the custom resolver interacts with your mesh:

  • special_price - the name of the field we are adding a custom resolver to

  • selectionSet - the information from the parent field, ConfigurableProduct, that the special_price field needs to resolve

  • root, context, args, and info - are the parameters provided to the new resolver function

Running the following query results in a response that lists the original maximum_price value and the special_price that was calculated using the DiscountsAPI file. In this example, we are searching for "sweater", but you could modify it to search for any products.

In the following response, you can see that the "Roxana Cropped Sweater" and the "Hanna Sweater" we specified in our discounts-api.json file have a special_price that is 10% less than their value.

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{
  products(search: "sweater") {
    items {
      name
      special_price
      price_range {
        maximum_price {
          final_price {
            value
          }
        }
      }
    }
  }
}
Jared HooverJeff Matthews
Last updated 9/11/2023
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