GraphQL

GraphQL will do to REST what JSON did to XML.

A Data Query Language

GraphQL is strongly typed, self-documenting, and embraces declarative data fetching, which allows clients to query for the exact data they need as well making it possible to build powerful and in-depth developer tools.

GraphQL server - A server which implements the GraphQL Specifications and exposes an API endpoint for clients to query.

GraphQL is typically used in scenarios where related data needs to be queried or in environments where multiple round trips to the server can negatively impact the customer experience.

Problems that GraphQL solves

The need to do multiple round trips to fetch data required by a view
Clients dependency on servers
The bad front-end developer experience
No Versioning of APIs
Get only what you asked

Problems with GraphQL

Resource Exhaustion Attacks (DOS) using overly complex queries
N+1 queries

Solution - https://github.com/facebook/dataloader

https://xuorig.medium.com/the-graphql-dataloader-pattern-visualized-3064a00f319f

GraphQL Core Concepts

Schema Definition Language (Used to define the schema of an API)
Defining Types (Type system allows us to check if query is valid or not before resolving the query)
Sending Queries and Mutations
- Queries with Arguments (extra information sent with query and mutation)
Mutations
- Creating new data
- Updating existing data
- Deleting existing data
Subscriptions
Resolvers
Variables
Inspection
- This allows us to know the schema using introspection and see documentation of all the endpoints with autocomplete in clients like Graphiql

Security

Timeout
Maximum Query Depth
Query Complexity
Throttling

How to GraphQL

In GraphQL, aTypeis an object that may contain multiplefields. Each field is calculated throughresolvers, that returns a value. A collection of types is called aschema. Every schema has a special type calledqueryfor getting data from the server andmutationfor sending data to the server.

Type
Query
Mutation
Resolver Tutorial
Queries
Mutations
Authentications
Links and Voting
Error Handling
Filtering
Pagination

https://hasura.io/blog/cursor-offset-pagination-with-hasura-graphql

Relay

Queries

mutation {
  createLink(
    url: "https://www.google.com"

    description: "Google"
  ) {
    id

    url

    description
  }
}
query {
  links {
    id

    url

    description
  }
}
mutation {
  tokenAuth(username: "deepak", password: "deepaksood") {
    token
  }
}

! - bang at the end of a type represents required

In graphene-python it is written as required=True

Client

Apollo
Relay
Graphiql
Insomnia
Postman

Schema stitching

Schema stitching is the process of creating a single GraphQL schema from multiple underlying GraphQL APIs.

One of the main benefits of GraphQL is that we can query all of our data as part of one schema, and get everything we need in one request. But as the schema grows, it might become cumbersome to manage it all as one codebase, and it starts to make sense to split it into different modules. We may also want to decompose your schema into separate microservices, which can be developed and deployed independently.

In both cases, we usemergeSchemasto combine multiple GraphQL schemas together and produce a merged schema that knows how to delegate parts of the query to the relevant subschemas. These subschemas can be either local to the server, or running on a remote server. They can even be services offered by 3rd parties, allowing us to connect to external data and create mashups.

https://www.apollographql.com/docs/graphql-tools/schema-stitching

Apollo Federation

Apollo Federation is an architecture for composing multiple GraphQL services into a single graph that addresses this need. Unlike other approaches such as schema stitching, it is based on a declarative composition programming model that allowsproper separation of concerns. This design allows teams to implement an enterprise-scale shared data graph as a set of loosely coupled, separately maintained GraphQL services.

https://principledgraphql.com/integrity#1-one-graph

https://www.apollographql.com/docs/apollo-server/federation/introduction

https://blog.apollographql.com/apollo-federation-f260cf525d21

https://github.com/apollographql/federation-demo