In a JavaScript GraphQL server, one common requirement is the ability to support multiple database engines. This allows developers to choose the database that best suits their needs and leverage its specific features. In this article, we will explore how to implement support for multiple database engines in a JavaScript GraphQL server using popular libraries like Apollo Server and Sequelize.

Setting Up the Project

Before we begin, let’s set up our project. We’ll start by creating a new directory and initializing a Node.js project:

mkdir my-graphql-server
cd my-graphql-server
npm init -y

Next, we need to install the required dependencies:

npm install apollo-server graphql sequelize

Connecting to Databases

To support multiple database engines, we need to establish connections to each database. For demonstration purposes, let’s assume we want to support both MySQL and PostgreSQL databases.

First, we need to install the respective database drivers:

npm install mysql2 pg

Next, we’ll create a file called database.js in the root of our project and add the following code:

const { Sequelize } = require('sequelize');

const mysqlDb = new Sequelize('mysql://username:password@localhost:3306/mydatabase');
const postgresDb = new Sequelize('postgres://username:password@localhost:5432/mydatabase');

module.exports = {
  mysqlDb,
  postgresDb,
};

Replace username, password, and mydatabase with your actual database credentials and names.

Building our GraphQL Server

Now, let’s create the main server file called server.js and set up Apollo Server with GraphQL:

const { ApolloServer, gql } = require('apollo-server');

const { mysqlDb, postgresDb } = require('./database');

const typeDefs = gql`
  type Query {
    books: [Book]
  }

  type Book {
    id: ID!
    title: String
  }
`;

const resolvers = {
  Query: {
    books: () => {
      // Fetch books from the active database
      // Example implementation using Sequelize:
      // return mysqlDb.models.Book.findAll();
    },
  },
};

const server = new ApolloServer({ typeDefs, resolvers });

server.listen().then(({ url }) => {
  console.log(`Server running at ${url}`);
});

In this example, we define a basic Query type and a resolver for fetching books from the active database. Note that we haven’t implemented the actual database querying logic yet.

Deciding the Active Database

To decide which database to use at runtime, we can utilize environment variables or configuration files. For simplicity, let’s use an environment variable called DATABASE_ENGINE, which will represent the active database engine.

In server.js, we can modify the code to use the appropriate database connection based on the DATABASE_ENGINE environment variable:

const activeDatabase = process.env.DATABASE_ENGINE === 'mysql' ? mysqlDb : postgresDb;

const resolvers = {
  Query: {
    books: () => {
      return activeDatabase.models.Book.findAll();
    },
  },
};

Conclusion

By implementing support for multiple database engines in a JavaScript GraphQL server, we provide flexibility to developers to choose the database that best meets their needs. With the help of libraries like Apollo Server and Sequelize, connecting to different databases and querying data becomes more manageable.

Remember, always choose a database solution that aligns with your project requirements and consider factors like scalability, performance, and developer experience when making a decision.

#webdevelopment #javascript