README.md

HydraphQL

HydraphQL provides functionality to organize your Schema by reducing repetition and augmenting it with GraphQL modules defining new types and how to resolve them.

• Directives API
  • @field
  • @implements
  • @discriminates
  • @resolve
• Getting started
  • GraphQL Application
  • Extending Schema
  • @graphql-codegen/TypeScript

Directives API

With GraphQL modules you can structure your graphql code base, but you still have to write resolvers using TypeScript code. However, one of the most important advantages of HydraphQL is that most of the time you don't need to write any TypeScript at all. Instead, you can tell GraphQL what it should do just by adding hints directly to the Schema about which fields map to what. These hints are called directives.

The following directives will tell GraphQL how to write resolvers automatically, so that you don't have to.

@field

The @field directive allows you to access properties on an object using a given path. It allows you to specify a resolver for a field from the schema without actually writing a real resolver at all. Under the hood, it's creating the resolver for you. To see this in action, check out the catalog.graphql which uses the @field directive extensively module to retrieve properties like namespace, title and others.

1. Mapping namespace.name field from source data to Entity#name field:

type Entity {
  name: String! @field(at: "namespace.name")
}

2. If source path's fields contain dots { spec: { "data.label": "..." } }, you can use an array:

type Entity {
  label: String @field(at: ["spec", "data.label"])
}

3. You can specify a default value as a fallback if the field is not found:

type Entity {
  tag: String! @field(at: "spec.tag", default: "N/A")
}

@implements

The @implements directive allows you to inherit fields from another interface. We created this directive to make it easier to implement interfaces that inherit from other interfaces. It makes GraphQL types similar to extending types in TypeScript. In TypeScript, when a class inherits another class, the child class automatically inherits properties and methods of the parent class. This functionality doesn't have an equivalent in GraphQL. Without this directive, the Service interface in GraphQL would need to re-implement many fields that are defined on implemented interfaces which leads to lots of duplication.

1. Use this directive to define a new type that includes all of the properties of the parent interface.

type Service @implements(interface: "Component") {
  endpoint: String! @field(at: "spec.endpoint")
}

In the output schema it is transformed into:

type Service implements Component & Entity & Node {
  id: ID!
  name: String!
  kind: String!
  namespace: String!
  # ... rest `Entity` and `Component` fields ...

  endpoint: String!
}

@discriminates

The @discriminates directive tells the GraphQL App that an interface be discriminated by a given value to another interface or a type. The value by path from with argument is used to determine to which type the interface should be resolved.

interface Entity
  @implements(interface: "Node")
  @discriminates(with: "kind") {
    # ...
  }

type Component @implements(interface: "Entity") {
  # ...
}
type Service @implements(interface: "Entity") {
  # ...
}

NOTE: In this example if we have data of Entity type and it has kind field with Component value, that means data will be resolved to Component type

opaqueType

There is a special case when your runtime data doesn't have a value that can be used to discriminate the interface or there is no type that matches the value. In this case, you can define opaqueType argument

interface Entity
  @implements(interface: "Node")
  @discriminates(with: "kind", opaqueType: "OpaqueEntity") {
    # ...
  }

In this case, if the value of kind field doesn't match with any schema type, the OpaqueEntity type will be used. You don't need to define this type, the GraphQL plugin will generate it for you.

There is another way to define opaque types for all interfaces by using generateOpaqueTypes option for GraphQL plugin.

aliases

By default value from with argument is used to find a type as-is or converted to PascalCase. Sometimes you need to match the value with a type that has a different name. In this case, you can define aliases argument.

interface API
  @implements(interface: "Node")
  @discriminates(with: "spec.type", aliases: [{ value: "grpc", type: "GrpcAPI" }]) {
    # ...
  }

type GrpcAPI @implements(interface: "API") {
  # ...
}

This means, when spec.type equals to grpc, the API interface will be resolved to GrpcAPI type.

@resolve

The @resolve directive is similar to the @field directive, but instead of resolving a field from the source data, it resolves a field from a 3rd party API. This is useful when you want to add fields to your schema that are not available in the source data, but are available from another API.

1. To achieve that first of all you need to create a DataLoader with createLoader function

import querystring from "querystring";
import { createLoader, NodeQuery } from "@frontside/hydraphql";

export const loader = createLoader({
  async ExampleCom(queries: NodeQuery[]) {
    return Promise.all(
      queries.map(async ({ ref, args }) => {
        const response = await fetch(
          `https://example.com/api/${ref}?${querystring.stringify(args)}`,
        );
        return response.json();
      }),
    );
  },
});

2. Then you can use the @resolve directive with specifying the loader name of your API:

type Project {
  tasks: [Task!] @resolve(at: "spec.projectId", from: "ExampleCom")
}

Getting started

GraphQL Application

Since HydraphQL uses GraphQL Modules createGraphQLApp returns a GraphQL Application which can be used with all popular GraphQL servers like apollo-server, express-graphql, graphql-yoga and others.

1. Create an application by using createGraphQLApp function

import {
  createGraphQLApp,
  createLoader,
  NodeQuery,
} from "@frontside/hydraphql";
import modules from "./modules";

export async function main() {
  const application = await createGraphQLApp({ modules });
  const loader = createLoader({
    async MyAPI(queries: NodeQuery[]) {
      // ...
    },
  });

  //...
}

2. Use the application with your GraphQL server

NOTE You can find a simple example of how to use HydraphQL with graphql-yoga in examples/graphql-yoga directory.

Extending your schema with a custom module

To extend your schema, you will define it using the GraphQL Schema Definition Language, and then (optionally) write resolvers to handle the various types which you defined.

1. Create modules directory where you'll store all your GraphQL modules, for example in ./src/modules
2. Create a module directory my-module there
3. Create a GraphQL schema file my-module.graphql in the module directory

extend type Query {
  hello: String!
}

This code adds a hello field to the global Query type. Next, we are going to write a module containing this schema and its resolvers.

4. Create a GraphQL module file my-module.ts in the module directory

import { loadFilesSync } from "@graphql-tools/load-files";
import { createModule } from "graphql-modules";

export const myModule = createModule({
  id: "my-module",
  dirname: __dirname,
  typeDefs: loadFilesSync(require.resolve("./my-module.graphql")),
  resolvers: {
    Query: {
      hello: () => "world",
    },
  },
});

@graphql-codegen/TypeScript

If you use @graphql-codegen to generate an output schema to use it for validating frontend queries and/or TypeScript to have type checking in GraphQL modules resolvers, you'll need modify your @graphql-codegen config.

1. First of all create a schema.ts file with transformSchema function and pass all your GraphQL files

// ./src/schema.ts
import { transformSchema } from "@frontside/hydraphql";
import { printSchemaWithDirectives } from "@graphql-tools/utils";
import { MyModule } from "./modules/my-module/my-module";

export const schema = printSchemaWithDirectives(transformSchema([MyModule]));

2. Then you need to update schema option in your codegen.ts

import { CodegenConfig } from "@graphql-codegen/cli";
import { schema } from "./src/schema";

const config: CodegenConfig = {
  schema,
  generates: {
    /* ... */
  },
};

export default config;