wilhelmberggren / graphql-service-from-schema

Exploration of generating a service from a GraphQL schema

What

Generate a backend from a GraphQL schema, using a custom directive called @SQL.

Live Example (in a free tier container)

@SQL(command: "create table if not exists users(id text, username text);")
type User {
  id: ID!,
  username: String,
}

type Query {
  user(id: ID!): User @SQL(command: "select * from users where id = :id")
  users(first: Int!, offset: Int!): [User] @SQL(command: "select * from users limit :first offset :offset")
}

type Mutation {
  createUser(username: String): User @SQL(command: "insert into users ( id, username ) values ( :id, :username )")
}

How

Resolvers are generated by parsing the schema. Annotate object descriptions on how to create a SQLite table, and fields on how to fetch them.

Simply write your schema in schema.gql and run yarn dev.

Alternatively, for a "production" docker container, run yarn docker

Tools

This is written using these libraries:

• better-sqlite3: a fast library for using SQLite
• graphql: the official library for parsing and printing GraphQL syntax
• apollo-server: the easiest to use GraphQL server

Tour

This project was made to be as minimal as possible. Here are the files:

generate.ts

getCommands

Takes in a parsed GraphQL schema, and returns each SQL command which defines how to create an SQL table for its respective object type.

getResolvers

Takes in a parsed GraphQL schema, and for each field which has a defined SQL command. Returns a resolver which executes that command using initDb.ts/makeQuery.

db.ts

initDb

Takes in a parsed GraphQL schema, and uses the aforementioned getCommands to execute each object's respective table.

makeResolver

Takes in the name of a root, a field and a command to access that field. Returns a resolver which executes that command.

server.ts

The entrypoint of the service. Parses the typeDefs, initialises the database and starts the server with the generated resolvers.

TODO:

• Look into adding dataloaders based on @key directive
• Better Federation support