decapi

What is decapi?

decapi is a set of decorators for creating GraphQL APIs in typescript. Write your types and GQL schema at once killing two birds with one stone.

• Documentation

Examples:

• Basic Express example
• Typeorm integration example
• Forward resolution - eg. query only needed db fields
• Nested mutations or queries
• Custom decorators / Higher order decorators
• Serverless eg. AWS Lambda
• Merge schemas

Basic example

Example below is able to resolve such query

query {
  hello(name: "Bob") # will resolve to 'Hello, Bob!'
}

import { SchemaRoot, Query, compileSchema } from 'decapi'

@SchemaRoot()
class SuperSchema {
  @Query()
  hello(name: string): string {
    return `Hello, ${name}!`
  }
}

const compiledSchema = compileSchema(SuperSchema)

compiledSchema is a regular GQL executable schema compatible with graphql-js library.

To use it with express, you'd have to simply:

import express from 'express'
import graphqlHTTP from 'express-graphql'

const app = express()

app.use(
  '/graphql',
  graphqlHTTP({
    schema: compiledSchema,
    graphiql: true
  })
)
app.listen(3000, () =>
  console.log('Graphql API ready on http://localhost:3000/graphql')
)

Although it is encouraged to prefer fastify as it is a bit faster when used with jit.

Adding nested types

For now, our query field returned scalar (string). Let's return something more complex. Schema will look like:

mutation {
  createProduct(name: "Chair", price: 99.99) {
    name
    price
    isExpensive
  }
}

Such query will have a bit more code and here it is:

import {
  SchemaRoot,
  Query,
  ObjectType,
  Field,
  Mutation,
  compileSchema
} from 'decapi'

@ObjectType({ description: 'Simple product object type' })
class Product {
  @Field()
  name: string

  @Field()
  price: number

  @Field()
  isExpensive() {
    return this.price > 50
  }
}

@SchemaRoot()
class SuperSchema {
  @Mutation()
  createProduct(name: string, price: number): Product {
    const product = new Product()
    product.name = name
    product.price = price
    return product
  }
}

const compiledSchema = compileSchema(SuperSchema)

Setting the type explicitly

In previous examples, decapi was able to determine the type of every field from typescript type definitions.

There are, however cases where we have to define them explicitly.

• We want to specify whether field is nullable or not
• We want to be explicit about if some number type is Float or Int (GraphQLFloat or GraphQLInt) etc
• Function we use returns type of Promise<SomeType> while field itself is typed as SomeType
• List (Array) type is used. (For now, typescript Reflect api is not able to guess type of single array item)

For major version 1.0.0 we will use https://github.com/rezonant/typescript-rtti so it will be able to determine all types directly from the TS type. This is WIP ATM.

Let's modify our Product so it has additional categories field that will return array of strings. For the sake of readability, let's ommit all fields we've defined previously.

@ObjectType()
class Product {
  @Field({ type: [String] }) // note we can use any native type like GraphQLString!
  categories(): string[] {
    return ['Tables', 'Furniture']
  }
}

We've added { type: [String] } as @Field options. Type can be anything that is resolvable to GraphQL type

• Native JS scalars: String, Number, Boolean, Date.
• Any type that is already compiled to graphql eg. GraphQLFloat or any type from external graphql library etc
• Any class decorated with @ObjectType
• Single element array for list types eg. [String] or [GraphQLFloat]

Writing Asynchronously

Every field function we write can be async and return Promise. Let's say, instead of hard-coding our categories, we want to fetch it from some external API:

@ObjectType()
class Product {
  @Field({ type: [String] }) // note we can use any native type like GraphQLString!
  async categories(): Promise<string[]> {
    const categories = await api.fetchCategories()
    return categories.map((cat) => cat.name)
  }
}

Compared to type-graphql

There is a much more popular library with the same goals-so what makes decapi different? Decapi has smaller API surface-it only has hooks on top of the basic decorators for constructing schemas. Whereas type-graphql has authorization, middleware, guards. Also decapi supports graphql v16. Typegraphql is still only supporting Graphql v15

Why forking?

I wanted to contribute to typegql and work on it together with @pie6k, but it soon became obvious that we both have something different in mind. Just to briefly summarise the differences:

• decapi has @DuplexObjectType and @DuplexField
• decapi supports interfaces and mixins
• decapi can infer Date type
• decapi has castTo Field config
• InputObjectType argument passed to Field/Query method is not just a plain object, but an instance of it's class.
• decapi allows you to have an empty object type-you can populate it with fields at runtime

Before 1.0.0

Before version 1.0.0 consider APIs of decapi to be subject to change. We encourage you to try this library out and provide us feedback so we can polish it to be as usable and efficent as possible.

TC39 decorators proposal

Please if you enjoy decapi, go and star repo with the proposal-decorators . That's a way to show the TC39 members that you are using decorators and you want to have them in the language.