01_GraphQL101.md

Intro to GraphQL

Getting started with GraphQL!

https://tech.kakao.com/2019/08/01/graphql-basic/

https://www.slideshare.net/shilpe34/typescript-200-graphql-179690400

What is GraphQL?

Query Language for APIs!

• Query Language like SQL (Structured Query Language)
  • but, there's a big difference in linguistic structure
    • As a result, the utilization of these two is different
    • Purpose of use
      • sql : Purpose is to efficiently retrieve data stored in DB
      • gql : Purpose is for Web Client to efficiently retrieve data from server
    • Calling
      • sql : Written and called in Backend system
      • gql : Written and called in Client system
• Can load a lot of data with a single request
• Type system
• Provides powerful developer tools

Serverside GraphQL application

• Takes queries written in gql as input, processes the queries and returns the results back to client
• GraphQL server

Differences between REST API and GraphQL API

• REST API

  • Various Endpoints exist because they combine URL, METHOD, etc.
    • Database SQL query differs for each Endpoint

• gql API

  • Only one Endpoint exists
  • The type of data to load is determined through query combinations
    • Database SQL query differs for each gql schema type

The advantages and disadvantages of each change depending on the configured infrastructure, business model, and purpose of use!

schema / type

ex)

type Character {
    name: String!
    appearIn: [Episode!]!
}

• Object type : Character
• Field : name, appearIn
• Scala type : String, Id, Int etc.
• ! : Required value (non-nullable)
• [ ,] : Array

Resolver

• gql query parsing is handled by most gql libraries
  • but, the specific process of retrieving data is handled by resolver and must be implemented directly!
• If the field is a scalar value (primitive type like string or number), execution terminates
  • That is, no more chained resolver calls occur