Basic components of GraphQL — Schema , Queries

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Basic components of GraphQL —
1. Schema
2. Query

Schema —

schema defines the structure, types, and relationships of the data available in your GraphQL API. It acts as a contract between the server and the clients, specifying what operations can be performed and what data can be accessed.

A GraphQL schema consists of two main components: types and fields.

Queries —
Queries allow clients to fetch data from the API. They are read-only operations and do not modify any data. For example, a client can send a query to retrieve a user’s details.

type Query {
  book(id: ID!): Book
  allBooks: [Book!]!
}

type Book {
  id: ID!
  title: String!
  publicationYear: Int!
  author: Author
}

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

example —
In this example, we have two main types: “Book” and “Query”.

The “Book” type represents a book object with the following fields:

• id (of type ID): An identifier for the book.
• title (of type String): The title of the book.
• author (of type Author): the relationship between a book and its author. It references the Author type.
• publicationYear (of type Int): The year the book was published.

Author: Represents an author object with the following fields:

• id (of type ID): An identifier for the author.
• firstName (of type String): The first name of the author.
• lastName (of type String): The last name of the author.

The “Query” type represents the available queries in our API. It includes the following fields:

• book (of type Book): A query that takes an id argument and returns a single book based on the provided ID.
• allBooks (of type [Book!]!): A query that returns a list of all books.

send queries —
clients can send queries to retrieve specific books by ID or fetch all the books available in the API.
For example, a client could send the following GraphQL query:
Query-1:

query {
  book(id: "123") {
    title
    publicationYear
  }
}

asks for the title, and publication year of a book with the ID “123”.
and Server will then respond with the corresponding book object:

{ "data": { 
            "book": { 
                      "title": "Sample Book", 
                      "publicationYear": 2020 
                    }
          } 
}

Query-2:

query {
  book(id: "123") {
    title
    author {
      firstName
    }
    publicationYear
  }
}

the query asks for the title, author (including the firstName and lastName), and publicationYear fields of the book with the ID "123".
server response will be

{
  "data": {
    "book": {
      "title": "Sample Book",
      "author": {
        "firstName": "John",
      },
      "publicationYear": 2021
    }
  }
}

Query-3

query {
  book(id: "123") {
    title
    publicationYear
  }
  allBooks {
    title
    author
    publicationYear
  }
}

The server’s response could be structured as follows:

{
  "data": {
    "book": {
      "title": "Sample Book",
      "author": {
        "firstName": "John",
        "lastName": "Doe"
      },
      "publicationYear": 2021
    },
    "allBooks": [
      {
        "title": "Book 1",
        "author": {
          "firstName": "Jane",
          "lastName": "Smith"
        },
        "publicationYear": 2022
      },
      {
        "title": "Book 2",
        "author": {
          "firstName": "Mark",
          "lastName": "Johnson"
        },
        "publicationYear": 2023
      },
      {
        "title": "Book 3",
        "author": {
          "firstName": "Sarah",
          "lastName": "Williams"
        },
        "publicationYear": 2021
      }
    ]
  }
}