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GraphQL Mesh

GraphQL Mesh

Query anything, run anywhere.

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Extending the Unified Schema#

We saw on the "How to: Combine multiple Sources" guide that additionalResolvers could be used to shape and augment the Unified Schema with custom resolvers.

However, the additionalResolvers value can also be the path to a JavaScript/TypeScript file that exports the custom resolvers implementation.



Programatic additionalResolvers#

In our "How to: Combine multiple Sources" Gateway, the additionalResolvers could have been provided programatically as shown in the multiple-sources-prog-resolvers example.

The below meshrc.yaml configuration add the following fields:

  • Store.bookSells: [Sells!]!: to get the selling from a given store
  • Book: to get the book of a given store selling record
  • authors_v1_Author: to get the author of a book


sources: # ... transforms: # ... additionalTypeDefs: | extend type Store { bookSells: [Sells!]! } extend type Sells { book: Book } extend type Book { author: authors_v1_Author } additionalResolvers: - "./resolvers"


import { Resolvers } from './.mesh' const resolvers: Resolvers = { Book: { author: { selectionSet: /* GraphQL */` { authorId } `, resolve: async (root, _args, context, info) => { return await context.Authors.Query.authors_v1_AuthorsService_GetAuthor({ root, args: { input: { id: root.authorId, } }, context, info, }) } } }, Store: { bookSells: { selectionSet: /* GraphQL */` { id } `, resolve: async (root, _args, context, info) => { return await context.Stores.Query.bookSells({ root, args: { storeId: }, context, info }) } } }, Sells: { book: { selectionSet: /* GraphQL */` { bookId } `, resolve: async (root, _args, context, info) => { return await{ root, args: { id: root.bookId }, context, info }) } } } } export default resolvers

Mesh relies on GraphQL Code Generator to generate the Resolvers type that gives you access to:

  • fully typed resolvers map
  • fully typed SDK (through the context) to fetch data from Sources

Using the SDK to fetch Sources#

Let's take a closer look at the resolver implementation.

The resolver is accessing the "Authors" source SDK through the context to fetch data from the authors_v1_AuthorsService_GetAuthor(id: ID!) Query as follows:

await context.Authors.Query.authors_v1_AuthorsService_GetAuthor({ root, args: { input: { id: root.authorId, } }, context, info, })

authors_v1_AuthorsService_GetAuthor is a generated SDK method that allows to query our gRPC Books Source as it was a GraphQL Schema.

Any SDK method take the following arguments:

  • root, context and info are mandatory parameters that we forward from the resolvers calling the method
  • args: arguments to pass to the Mutation or Query
  • selectionSet: allows to specify a selection on the Query/Mutation to fetch nested data
  • valuesFromResults: allows to provide a function to transform the results (if the result is an array, the function will be mapped to each element)

Note: valuesFromResults, compared to selectionSet helps to "flatten"/"unnest" data from results



Going further#

Transforms such as "Resolvers composition", Extend" and "Hoist Field" also helps in shaping and extending the Unified Schema.