Graphql.md

Graphql

• GraphQL is a query language for APIs and a runtime for fulfilling those queries with your data

• Graphql is an API Standard

• Enables declarative data fetching - client specifies exactly what data it wants from an API and that data is returned in response.

• Graphql server exposes single end point and responds to queries with prdata that a client asked for

• Graphql has strong type system which give us an idea of capabilities of an API.

• Schema Definition Language(SDL) language is used to define schema of an API.

type Person{
  name: String!
  age: Int!
  posts: [Post!]!
}
  
type Post{
  title:String!
  author:Person!
}
     
/* Example of a query */          
{
  allPersons {
    name
  }
}

• Here allPersons is the root field of the query. Everything that follows the root field is the payload.
• In GraphQL, each field can have zero or more arguments if that’s specified in the schema.

Important concepts of graphql

• Schema

• Query

• Mutation

• Subscription

• Resolver function

• Generally, a schema is simply a collection of GraphQL types. However, when writing the schema for an API, there are some special root types

  /* Schema Example */
type Query {
  allPersons(last: Int): [Person!]!
}

type Mutation {
  createPerson(name: String!, age: Int!): Person!
}

type Subscription {
  newPerson: Person!
}

type Person {
  name: String!
  age: Int!
  posts: [Post!]!
}

type Post {
  title: String!
  author: Person!
}