karkranikhil / graphql-car-demo

Building an application using react, MySQL and graphql to demonstrate the concept

GraphQL

It is a Query language for an API. It means you can specify in your application what part of your data structure you want to import and use within the application.

• Get the data you need exactly.

• Uses a type system

  type Query{
     employees:[Employee]
     employee(empid:ID!)Employee
  }
  
  type Employee{
     empid:ID
     fname:String!
     lname:String!
     email:String!
  }
  

Schemas and Types

• Schema also referred as Type Definitions (type defs)
• Specifies the available data for reading/writing

It has a mandatory Query type that defines what to query for.

• a) Type specifies the type for a given field like String, Int, Boolean etc.
• b) Custom types can be used
• c) Exclamation mark: non-nullable field
• d) ID - internal identifies (mainly used for caching)

Resolver

It's a function that defines where the data is coming from.Each top level Query type needs a resolver

It works with four parameters

• 1. object - contain the result on the parent
• 2. Args - argument mentioned in Query like empid
• 3. Context - An object share by all resolvers - helpful in authentication
• 4. Info - contains execution information

Query

It return data based on the Schema and the resolver

Graphql JS based implementation

1. Relay
2. Apollo
3. FetchQL
4. Express-graphql
5. Graphql-sequelize

gql

It allow us to create a scheme using JS es6 template literal syntax

Relationship between types using graphql

Suppose we have Car query and User query then we have to make a relationship between these two queries like Each user belong to car and car belong to user

Mutation

If you want to update the data using Graphql we called it as mutation. It is a buil in data type

Queries used

  {

     /* get all users name*/
     users{
        name
     }
     /* get users name and car make using id*/
     user(id:1){
        name
        car{
           make
        }
     }
     /* get car make and owner name using id*/
     car(id:1){
        make
        owner{
           name
        }
     }
     /* get cars make, model and owner name */
     cars{
        make
        model
        owner{
           name
        }
     }
     /* Mutation to make user*/
     mutation{
     makeUser(id:4,name:"nikhil"){
        name
     }
     }
     /* Mutation to create car*/
     mutation{
     createCar(id:4, make:"Toyota",model:"Etios", color:"Black"){
        make
     }
     }
     /* Mutation to remove user based on ID*/
     mutation{
     removeUser(id:4)
     }

     /* Mutation to remove car based on ID*/
     mutation{
     removeCar(id:3)
     }

  }