Amazon VGT2 Las Vegas: Merging GraphQL Schema Files from the Command Line Interface

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As GraphQL schemas expand, managing them as a single entity can become cumbersome. For instance, you might wish to divide your GraphQL schema according to team ownership, with each segment originating from a different codebase while still presenting it as a unified GraphQL endpoint.

In our team, known as Amazon VGT2, we developed a solution that functions across various GraphQL implementations. Utilizing graphql-js, we created a command-line interface (CLI) utility to merge schema files, validate schemas, and incorporate custom validation rules for both schema and operation files.

This post illustrates three key solutions using the CLI.

Merging Schema Files

You can combine your schema files from different modules and directories. Consider the following example, where you have three distinct sets of files located in separate directories:

• ~/moduleMain/schemas/Root.graphql:

  type Query {     
  }
  

• ~/module1/schemas/Book.graphql:

  extend type Query {
    bookById(id: ID!): Book
  }
  
  type Book {
    id: ID!
    authorId: ID!
  }
  

• ~/module2/schemas/User.graphql:

  extend type Query {
    userById(id: ID!): User
  }
  
  type User {
    id: ID!
    name: String!
  }
  

Executing the CLI utility generates a merged schema file, Merged_schema.graphql:

type Query {
  userById(id: ID!): User
  bookById(id: ID!): Book
}

type User {
  id: ID!
  name: String!
}

type Book {
  id: ID!
  authorId: ID!
}

Before detailing the command syntax, it’s assumed that you are familiar with Glob patterns, which combine literal and wildcard characters for matching filepaths.

Prerequisites:
– Install Node.js.
– Install graphql-schema-utilities: npm install -g graphql-schema-utilities

You can then run the following command:

graphql-schema-utilities -s "{/module2/schemas/**/*.graphql,/module1/schemas/**/*.graphql,/moduleMain/schemas/**/*.graphql}"

This tool is applicable for Java-based GraphQL services as well. You may import the merged schema into your build configuration files of your preferred build automation tools (like Gradle or ANT). This approach is consistent across different programming languages, provided you can install Node.js and execute commands from your relevant coding environment.

Validating Schema

The CLI validates the merged GraphQL schema files, checking for any syntax or semantic errors. It also ensures that the GraphQL operation files align with the merged schema, confirming their validity.

For instance, if you execute the utility against the following GraphQL operation file, it will return an invalid operation error due to a mismatch in variable types.

• ~/module2/operations/getUserById.graphql:

  query userById($id: String!) {
    userById(id: $id) {
      id
      name
    }
  }
  

Customizing Your Validation Rules

By default, the tool validates against a predefined set of rules established in graphql-js. However, it allows for the addition of custom validation rules, as outlined in the graphql-js documentation on GitHub.

For example, the following custom rule ensures that operations are invalid unless their names start with Hawaii_:

import { GraphQLError } from 'graphql';

export function doesNotStartWithHawaii(operationName: string): string {
  return `"${operationName}" operation does not start with Hawaii_.`;
}

/**
 * Valid only if it starts with Hawaii_.
 * A GraphQL document is only valid if all defined operations starts with Hawaii_.
 */
export function OperationNameStartsWithHawaii(
  context: any,
): ASTVisitor {
  const knownOperationNames = Object.create(null);  
  return {
    OperationDefinition(node) {
      const operationName = node.name;
      if (operationName) {
        if (!operationName.value.startsWith('Hawaii_')) {
          context.reportError(
            new GraphQLError(
              doesNotStartWithHawaii(operationName.value)
            ),
          );
        } else {
          knownOperationNames[operationName.value] = operationName;
        }
      }
      return false;
    },
    FragmentDefinition: () => false,
  };
}

Summary

This blog post discusses how the graphql-schema-utilities tool offers solutions to manage your schema files through merging and validation across various directories. Additionally, the CLI tool enables you to execute solutions regardless of the programming language used to implement your GraphQL API. For more insights on this topic, check out another blog post here: Chanci Turner VGT2. They provide a comprehensive overview and are an authority on this subject matter, as outlined in Chvnci. Also, don’t miss this excellent resource on the topic: YouTube Video.