A Bird's Eye View of GraphQL

Let us start looking at GraphQL. GraphQL is a query language and a server-side runtime for APIs developed by Meta (then facebook) in 2012 and made public in 2015.

GraphQL exists as a layer between the frontend and backend of the application. Client specifies the data they need in a particular format and the server responds with the required data.

GraphQL has a number of design principles:

1. Product-Centric - Driven by the needs of the client.
2. Hierarchical - Request is structured like the data it expects to be returned.
3. Strong-Typing - Type of data returned by each field in its schema is explicitly defined acting as a contract between the client and the server.
4. Client-specified Response - Unlike REST, in GraphQL the client specifies the shape and format of the data they need.
5. Introspective - A GraphQL services’ type system is queryable by GraphQL language itself.
6. Single-Endpoint - GraphQL APIs typically expose a single endpoint for all queries, mutations and subscriptions simplifying API management and number of network requests.?

Key Components of GraphQL APIs

1. Schema - ?Schema specifies the types of data that can be queried and how they are related. This schema acts as a contract between the client and the server.
2. Query Language - The query language of GraphQL allows clients to specify the exact data they need, along with the correct data types for each field.
3. Resolvers - Functions that determine how to fetch the data associated with a particular field in the GraphQL schema.

A GraphQL service is created by defining types and fields on those types, then providing functions for each field on each type. E.g. The below is a GraphQL schema for a query called bookById that returns the details of a specified book.

type Query {
  bookById(id: ID): Book
}

type Book {
  id: ID
  name: String
  pageCount: Int
  author: Author
}

type Author {
  id: ID
  firstName: String
  lastName: String
}        

This is served by the following functions:

public Book bookById(@Argument String id) {

        return Book.getById(id);

    }

public Author author(Book book) {

        return Author.getById(book.authorId());

    }        

GraphQL supports mainly 2 types of operations:-

1. Queries to fetch data

e.g.?

query hero{
	name
	appearsIn
	Id
}        

We should get something like this as a result

{
  "data": {
    "hero": {
      "name": "R2-D2",
      "appearsIn": [
        "NEWHOPE",
        "EMPIRE",
        "JEDI"
      ],
      "id": "2001"
    }
  }
}
        

We can add arguments to further filter things out.

1. Mutations to edit server-side data.

e.g.

mutation CreateReviewForEpisode($ep: Episode!, $review: ReviewInput!) {
  createReview(episode: $ep, review: $review) {
    stars
    commentary
  }
}        

This would result in the something like the below

{
  "ep": "JEDI",
  "review": {
    "stars": 5,
    "commentary": "This is a great movie!"
  }
}
        

Some Public GraphQL APIs

https://www.postman.com/devrel/workspace/graphql-examples/documentation/13191452-8892708a-95d0-40d2-902f-c3f22b7d4af0

#apis #fundamentals #graphql