12+ GraphQL Interview Questions (ANSWERED) To Check in 2020

No. GraphQL is often confused with being a database technology. This is a misconception, GraphQL is a query language for APIs - not databases. In that sense it’s database agnostic and can be used with any kind of database or even no database at all.

GraphQL is a query language created by Facebook in 2012 which provides a common interface between the client and the server for data fetching and manipulations.

The client asks for various data from the GraphQL server via queries. The response format is described in the query and defined by the client instead of the server: they are called client‐specified queries.
The structure of the data is not hardcoded as in traditional REST APIs - this makes retrieving data from the server more efficient for the client.

A successful GraphQL query is supposed to return a JSON object with a root field called "data". If the request fails or partially fails (e.g. because the user requesting the data doesn’t have the right access permissions), a second root field called "errors" is added to the response:

    {
      "data": { ... },
      "errors": [ ... ]
    }

Every GraphQL server has two core parts that determine how it works: a schema and resolve functions.

The schema is a model of the data that can be fetched through the GraphQL server. It defines what queries clients are allowed to make, what types of data can be fetched from the server, and what the relationships between these types are.

Consider:

type Author {
  id: Int
  name: String
  posts: [Post]
}
type Post {
  id: Int
  title: String
  text: String
  author: Author
}
type Query {
  getAuthor(id: Int): Author
  getPostsByTitle(titleContains: String): [Post]
}
schema {
  query: Query
}

The main and most important difference between REST and GraphQL is that GraphQL is not dealing with dedicated resources, instead everything is regarded as a graph and therefore is connected and can be queried to app exact needs.

One common concern with GraphQL, especially when comparing it to REST, are the difficulties to maintain server-side cache. With REST, it’s easy to cache the data for each endpoint, since it’s sure that the structure of the data will not change.

With GraphQL on the other hand, it’s not clear what a client will request next, so putting a caching layer right behind the API doesn’t make a lot of sense.

Server-side caching still is a challenge with GraphQL.

Authentication and authorization are often confused. Authentication describes the process of claiming an identity. That’s what you do when you log in to a service with a username and password, you authenticate yourself. Authorization on the other hand describes permission rules that specify the access rights of individual users and user groups to certain parts of the system.

Authentication in GraphQL can be implemented with common patterns such as OAuth.

To implement authorization, it is recommended to delegate any data access logic to the business logic layer and not handle it directly in the GraphQL implementation.

Key concepts of the GraphQL query language are:

• Hierarchical
• Product‐centric
• Strong‐typing
• Client‐specified queries
• Introspective