{"id":22814316,"url":"https://github.com/devinterview-io/graphql-interview-questions","last_synced_at":"2025-06-15T07:38:50.729Z","repository":{"id":49403325,"uuid":"326920622","full_name":"Devinterview-io/graphql-interview-questions","owner":"Devinterview-io","description":"🟣 GraphQL interview questions and answers to help you prepare for your next technical interview in 2024.","archived":false,"fork":false,"pushed_at":"2024-01-07T17:42:27.000Z","size":24,"stargazers_count":34,"open_issues_count":1,"forks_count":6,"subscribers_count":1,"default_branch":"main","last_synced_at":"2025-04-22T18:53:44.299Z","etag":null,"topics":["coding-interview-questions","coding-interviews","graphql","graphql-interview-questions","graphql-questions","graphql-tech-interview","interview-practice","interview-prep","interview-preparation","leetcode-questions","leetcode-solutions","programming-interview-questions","software-developer-interview","software-engineer-interview","software-engineering","technical-interview-questions","web-and-mobile-development-interview-questions"],"latest_commit_sha":null,"homepage":"https://devinterview.io/","language":null,"has_issues":true,"has_wiki":null,"has_pages":null,"mirror_url":null,"source_name":null,"license":null,"status":null,"scm":"git","pull_requests_enabled":true,"icon_url":"https://github.com/Devinterview-io.png","metadata":{"files":{"readme":"README.md","changelog":null,"contributing":null,"funding":null,"license":null,"code_of_conduct":null,"threat_model":null,"audit":null,"citation":null,"codeowners":null,"security":null,"support":null,"governance":null,"roadmap":null,"authors":null,"dei":null,"publiccode":null,"codemeta":null,"zenodo":null}},"created_at":"2021-01-05T07:27:23.000Z","updated_at":"2025-03-05T10:27:16.000Z","dependencies_parsed_at":"2025-04-22T18:41:34.263Z","dependency_job_id":"9a40d94e-ac29-432e-984d-acffceed45ae","html_url":"https://github.com/Devinterview-io/graphql-interview-questions","commit_stats":null,"previous_names":[],"tags_count":0,"template":false,"template_full_name":null,"purl":"pkg:github/Devinterview-io/graphql-interview-questions","repository_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/Devinterview-io%2Fgraphql-interview-questions","tags_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/Devinterview-io%2Fgraphql-interview-questions/tags","releases_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/Devinterview-io%2Fgraphql-interview-questions/releases","manifests_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/Devinterview-io%2Fgraphql-interview-questions/manifests","owner_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/owners/Devinterview-io","download_url":"https://codeload.github.com/Devinterview-io/graphql-interview-questions/tar.gz/refs/heads/main","sbom_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/Devinterview-io%2Fgraphql-interview-questions/sbom","host":{"name":"GitHub","url":"https://github.com","kind":"github","repositories_count":259941028,"owners_count":22935291,"icon_url":"https://github.com/github.png","version":null,"created_at":"2022-05-30T11:31:42.601Z","updated_at":"2022-07-04T15:15:14.044Z","host_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub","repositories_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories","repository_names_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repository_names","owners_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/owners"}},"keywords":["coding-interview-questions","coding-interviews","graphql","graphql-interview-questions","graphql-questions","graphql-tech-interview","interview-practice","interview-prep","interview-preparation","leetcode-questions","leetcode-solutions","programming-interview-questions","software-developer-interview","software-engineer-interview","software-engineering","technical-interview-questions","web-and-mobile-development-interview-questions"],"created_at":"2024-12-12T13:08:05.590Z","updated_at":"2025-06-15T07:38:50.705Z","avatar_url":"https://github.com/Devinterview-io.png","language":null,"readme":"# Top 100 GraphQL Interview Questions in 2025\n\n\u003cdiv\u003e\n\u003cp align=\"center\"\u003e\n\u003ca href=\"https://devinterview.io/questions/web-and-mobile-development/\"\u003e\n\u003cimg src=\"https://firebasestorage.googleapis.com/v0/b/dev-stack-app.appspot.com/o/github-blog-img%2Fweb-and-mobile-development-github-img.jpg?alt=media\u0026token=1b5eeecc-c9fb-49f5-9e03-50cf2e309555\" alt=\"web-and-mobile-development\" width=\"100%\"\u003e\n\u003c/a\u003e\n\u003c/p\u003e\n\n#### You can also find all 100 answers here 👉 [Devinterview.io - GraphQL](https://devinterview.io/questions/web-and-mobile-development/graphql-interview-questions)\n\n\u003cbr\u003e\n\n## 1. What is _GraphQL_ and how does it differ from _REST_?\n\n**GraphQL** is a highly efficient data query and manipulation language paired with a server runtime. It's designed to **optimize data fetching for clients** by allowing them to specify the shape and structure of the data they need.\n\nIn contrast, **REST** is an architectural style where clients interact with server endpoints (resources) using a standard set of HTTP methods.\n\n### Key Benefits of GraphQL over REST\n\n- **Efficiency**: GraphQL minimizes data over-fetching and under-fetching, ensuring that clients receive only the necessary data. In contrast, REST endpoints have fixed responses, potentially leading to data redundancy or under-supply.\n\n- **Flexibility**: With GraphQL, clients can specify the exact shape of the data they need. This is beneficial for applications with varying data requirements. REST endpoints deliver a pre-defined data set in their responses.\n\n- **Versioning \u0026 Documentation**: GraphQL obviates the need for versioning and keeps documentation centralized. In REST, version management and documentation are typically separate from the API, complicating the process.\n\n- **Data Validation**: GraphQL servers validate and type-check incoming requests. In REST, this is typically the client's responsibility.\n\n- **Network Efficiency**: GraphQL often makes fewer network calls when acquiring related resources, compared to REST, which could necessitate multiple requests for the same resources.\n\n- **Tooling \u0026 Ecosystem**: Both approaches enjoy extensive tooling support, but GraphQL's real-time introspection, strong type system, and auto-generation of documentation sets it apart. Additionally, GraphQL clients can benefit from query caching strategies.\n\n- **Cache Control**: REST APIs provide various caching strategies using standard HTTP mechanisms. **Apollo Federation** in GraphQL further refines these strategies, offering finer control over caching across federated services.\n\n- **Performance Optimizations**: Both REST and GraphQL can employ mechanisms like request throttling, but GraphQL's ability to batch multiple data requests into a single query contributes to improved performance.\n\n- **Response Compression**: For reducing data size, GraphQL can utilize techniques like query result compression, while REST APIs can use response compression.\n\n- **Data Consistency**: In a reliable setup, both REST and GraphQL can provide data consistency. However, when using GraphQL with subscriptions, real-time updates can be more straightforward to implement.\n\n### When to Use GraphQL or REST\n\n- **GraphQL**: Ideal for applications with diverse or changing data requirements, dynamic UIs demanding real-time data, or microservice architectures. Also suitable when the client and server are developed and maintained by the same team, ensuring end-to-end compatibility.\n\n- **REST**: Recommended when the application has straightforward data requirements, relies on well-established data models, or the client's front-end architecture implements one-to-one mapping with the server's resources.\n\n### Code Example: Basic Schema and Resolver\n\nHere is the GraphQL code:\n\n```graphql\ntype Query {\n  # Retrieves a list of all users\n  allUsers: [User]\n}\n\ntype User {\n  id: ID!\n  name: String!\n  email: String!\n}\n\n# Example Query: Fetch all user names and emails\nquery {\n  allUsers {\n    name\n    email\n  }\n}\n```\n\nNow, the equivalent REST endpoint for reference:\n\n```plaintext\nGET /api/users\n\nResponse Body:\n[\n  {\n    \"id\": 1,\n    \"name\": \"John Doe\",\n    \"email\": \"john.doe@gmail.com\"\n  },\n  {\n    \"id\": 2,\n    \"name\": \"Jane Smith\",\n    \"email\": \"jane.smith@gmail.com\"\n  }\n]\n```\n\u003cbr\u003e\n\n## 2. Explain the main components of the _GraphQL architecture_.\n\nThe **GraphQL architecture** revolves around several key components, each serving a distinct role in the broader ecosystem.\n\n### Core Components\n\n1. **Client**: The client initiates data requests, specifying their shape and content through GraphQL queries. This permits more streamlined data access compared to traditional REST operations.\n\n2. **Server**: It's the server's task to process incoming GraphQL queries and deliver the relevant data in response. This paradigm of executing GraphQL queries is defined as \"query execution.\"\n\n3. **Schema**: The schema serves as the contract between the client and the server, establishing the **type system**, namely the types of data available for interaction (e.g., `User`, `Post`) and the **operations** that can be performed (e.g., `Query`, `Mutation`).\n\n4. **Resolver Functions**: These functions are associated with each **field** in a GraphQL type and dictate how that field's data should be retrieved or manipulated. For instance, a resolver for a `user` field within a `Query` type might describe how to fetch a user.\n\n5. **Query Validator and Executor**: After a query is received, the server performs a two-stage process: **validation** (ensuring the query adheres to the schema) and **execution** (fetching data as per the validated query and its resolvers).\n\n### Supporting Components\n\n  - **Data Source**: Represents the origin of real data, like a database. Each resolver can pull data from different data sources, which can improve modularity and scalability.\n\n  - **Operations**: On the server, these can be of two types: `Query` for reading data and `Mutation` for modifying data. Additionally, one can write `Subscription` operations for real-time data updates.\n\n### Flow of Operations\n\n  - **Query**: Sent by the client to specify the data requirements. It's validated, and only if successful, the server operates on it.\n  \n  - **Validation**: The query is verified against the schema to confirm its correctness. If any elements in the query violate the schema, an error is sent back to the client.\n  \n  - **Execution**: The server employs the resolved functions to retrieve or process the required data, responding with the results in the expected format.\n\u003cbr\u003e\n\n## 3. Can you describe the structure of a _GraphQL query_?\n\nA **GraphQL query** specifies the data you seek and the shape you expect it back in. It's composed of **fields** nested within each other, forming a **query tree**.\n\n### Language Elements\n\n- **Fields**: The basic unit of a query, representing a piece of data you want to retrieve.\n  \n- **Arguments**: Used to customize the result of a field with specific parameters.\n\n- **Aliases**: Enables multiple references to the same field with different configurations.\n\n- **Fragments**: Reusable group of fields, improving the organization of query documents.\n\n- **Directives**: Provide conditional query execution and value manipulation.\n\n- **Operation Types**: Defines whether the query is for fetching data (`query`) or mutating data (`mutation`).\n\n### Query Example: Fetching a User's Name and Last 5 Posts On Most Recently Used Device\n\nGraphiQL Example:\n\n```graphql\nquery {\n  currentUser {\n    name\n    posts(last: 5)\n  }\n}\n```\n\nJSON Response that May be Returned:\n\n```json\n{\n  \"user\": {\n    \"name\": \"John Doe\",\n    \"posts\": [\n      // Array of post objects\n    ]\n  }\n}\n```\n\n### Query Syntax - Code Example: Firebase API\n\nHere is the **Node.js** code:\n\n  ```javascript\n  var query = /* GraphQL */ `{\n    currentUser {\n      name\n      posts(last: 5)\n    }\n  }`;\n\n  firebaseUserModel.query(query).then(response =\u003e {\n    console.log(\"User Data:\", response);\n  });\n  ```\n\u003cbr\u003e\n\n## 4. What are the core features of _GraphQL_?\n\nLet's look into the core features of **GraphQL**, a query language and runtime designed by Facebook to enable efficient data communication between the client and server.\n\n### Core Features\n\n- **Declarative Data Fetching**: Empowers clients to request exactly what they need. With REST, developers often over-fetch or under-fetch data, causing inefficiencies in both data transmission and rendering. In contrast, GraphQL allows clients to specify their data requirements, leading to more efficient and specific data retrieval.\n\n    - **Example**: Here is a structural query defined with GraphQL, automatically fetching necessary data.\n\n    ```graphql\n    query {\n      user(id: \"123\") {\n        name\n        posts {\n          title\n          content\n        }\n      }\n    }\n    ```\n\n- **Hierarchical Structure**: Data is structured as a graph. GraphQL directives, which are used to annotate and modify existing schema types, can be coupled with the query language to impose rules on the query execution. For instance, `@include` and `@skip` enable conditional fetching of fields.\n\n    - **Example**: The following query demonstrates conditional fetching using directives.\n\n    ```graphql\n    query {\n      user(id: \"123\") {\n        name\n        posts {\n          title\n          content\n          comments @include(if: $showComments)\n        }\n      }\n    }\n    ```\n\n- **Strongly-Typed Schema**: Businesses and developers can benefit from type safety, reducing errors and unexpected behaviors. Every GraphQL API is formed from a set of well-defined object types with precise fields. This type system is backed by a schema that needs to be explicitly declared and shared.\n\n  - **Example**: The schema-first approach uses SDL (Schema Definition Language) to define types and their relationships.\n\n    ```graphql\n    type User {\n        id: ID!\n        name: String!\n        age: Int\n    }\n    ```\n\n- **Single Endpoint for All Operations**: Simplifies the management and orchestration of data, as a single endpoint is utilized for all data interactions. This differs from REST-centric approaches, where endpoints are typically specific to resources or actions, leading to potential confusion in larger systems.\n\n- **Built-in Documentation**: Provides auto-generated and readily-accessible documentation, easing the burden of maintaining external documentation. This \"graphiql\" in-browser environment, often utilized during the development stage, allows an interactive exploration of the available API and assists in writing precise queries.\n\n- **Introspection**: Enables tools to query the GraphQL server itself for its schema. This meta-level functionality enhances the extensibility and productivity of developers by facilitating functionalities like dynamic query generation and language or platform-specific tooling.\n\n- **Real-time Data**: Through **Subscriptions,** GraphQL offers a method for the server to actively push data to clients, creating remarkable opportunities for real-time interactions in modern apps. Whether it's chat applications or collaborative documents, this feature provides a seamless experience for end-users.\n\n    - **Example**: A GraphQL query incorporating real-time data acquisition.\n\n    ```graphql\n    subscription {\n      newUser {\n        id\n        name\n      }\n    }\n    ```\n\n### Benefits of Using GraphQL\n\n- **Reduction in Over/Under Fetching**: Empowers clients to receive precisely the data they need, eradicating the efficiency challenges associated with over-fetching and under-fetching.\n\n- **Improved Frontend Autonomy**: Fosters frontend independence, allowing teams to evolve their applications without necessitating corresponding backend alterations.\n\n- **Enhanced Tooling and Efficiency**: The robust type system and schema enable advanced tooling and provide developers with comprehensive insights even at the time of query construction.\n\n- **Adaptability and Evolvability**: Facilitates a more streamlined development lifecycle, particularly in contexts featuring rapid evolution or requirements for distinct client applications like web, mobile, and IoT.\n\u003cbr\u003e\n\n## 5. What is a _GraphQL schema_ and why is it important?\n\n**GraphQL Schema** serves as the contract between client and server, outlining available data types, their relationships, and the API surface.\n\n### Core Schema Components\n\n#### Object Types\n\nData in GraphQL is wrapped in object types. Each type comprises a set of fields, which can be other object types or scalar types.\n\nExample:\n\nThe `User` type may comprise fields like `id` (a scalar) and `posts` (a list of the `Post` type).\n\n#### Scalar Types\n\nScalar types are the atomic data types of GraphQL. They include standard types like `String`, `Int`, `Float`, `Boolean`, and `ID`. Custom scalar types allow for tailored behaviors, like `DateTime` for consistent date representation.\n\n#### Query and Mutation Types\n\nBoth are **entry points** for the client:\n\n- **Query**: Specifies available read operations clients can invoke.\n- **Mutation**: Defines write operations.\n\nExample:\n\n```graphql\ntype Mutation {\n  createUser(name: String!): User\n}\n```\n\n#### Input Types\n\nThese represent data the client sends to the server during mutations. They are similar to object types but exclusively used as input.\n\nExample:\n\n```graphql\ninput UserInput {\n  name: String!\n}\n```\n\n#### Interfaces and Unions\n\nThese facilitate **complex type hierarchies**.\n\n- **Interfaces**: A collection of shared fields which GraphQL types can implement.\n- **Unions**: Acts as an \"or\" statement, allowing multiple types to be returned.\n\nExample:\n\n```graphql\ninterface Post {\n  content: String!\n  author: User!\n}\n\ntype TextPost implements Post {\n  content: String!\n  author: User!\n  wordCount: Int!\n}\n\ntype ImagePost implements Post {\n  content: String!\n  author: User!\n  imageUrl: String!\n}\n\ntype Query {\n  allPosts: [Post]!\n}\n```\n\n#### Directives\n\nThese are like annotations and can modify the behavior of an operation. While they don't define data types, they are still part of the type system.\n\nExample:\n\n```graphql\ndirective @auth on FIELD_DEFINITION\n\ntype User {\n  id: ID\n  email: String! @auth\n  password: String! @auth\n}\n```\n\n#### Enumerations\n\nThese are custom object types that enumerate a defined set of options.\n\nExample:\n\n```graphql\nenum UserRole {\n  ADMIN\n  USER\n}\n```\n\n#### Multiple Types\n\nA single GraphQL schema can **consist of various** types, including those mentioned above. Every field in the schema needs to resolve to one of the defined types.\n\n### Why Are Schemas Important?\n\n- **Clear Communication**: Schemas act as a clear API contract between the client and the server.\n- **Structured Data**: They define data types and relationships, ensuring a structured data model.\n- **Safety**: The schema helps in error detection and makes sure data types are consistently handled across the application.\n- **Ease of Collaboration**: Schemas ensure that a front-end and back-end developer can work independently as long as they adhere to the schema contract.\n- **Documentation Generation**: Schemas can be used to auto-generate developer-friendly documentation, promoting clarity and comprehension. \n\n### Schema Evolution\n\nA GraphQL schema, like any software, is **subject to change and evolution**. However, changes need to be managed to ensure query compatibility. Visual tools, versioning strategies, and strong communication between teams are vital for seamless schema evolution.\n\n#### Implementing Schemas and Types in Code\n\nBelow is the Node.js code:\n\n1. **Define Schema and Types** with GraphQL\n\n   ```javascript\n   const { GraphQLObjectType, GraphQLSchema, GraphQLString, GraphQLList, GraphQLNonNull, GraphQLInterfaceType } = require('graphql');\n\n   const UserType = new GraphQLObjectType({\n      name: 'User',\n      fields: () =\u003e ({\n         id: { type: GraphQLString },\n         name: { type: new GraphQLNonNull(GraphQLString) },\n         posts: {\n            type: new GraphQLList(PostType),\n            resolve: (user) =\u003e getUserPosts(user.id),\n         },\n      }),\n   });\n   \n   const PostType = new GraphQLInterfaceType({\n      name: 'Post',\n      fields: () =\u003e ({\n         content: { type: GraphQLString },\n         author: { type: UserType },\n      }),\n      resolveType: (post) =\u003e {\n         if (typeof post.wordCount !== 'undefined') {\n            return 'TextPost';\n         }\n         return 'ImagePost';\n      },\n   });\n   \n   module.exports = new GraphQLSchema({\n      types: [UserType, PostType],\n      query: new GraphQLObjectType({\n         name: 'RootQueryType',\n         fields: {\n            allPosts: {\n               type: new GraphQLList(PostType),\n               resolve: getAllPosts,\n            },\n         },\n      }),\n   });\n   ```\n\n2. **Specify Directives**\n\n   ```javascript\n   const { GraphQLDirective, DirectiveLocation, GraphQLString } = require('graphql');\n   \n   const authDirective = new GraphQLDirective({\n      name: 'auth',\n      description: 'Directive to control access to secure fields.',\n      locations: [DirectiveLocation.FIELD_DEFINITION],\n      args: {\n         requires: { type: new GraphQLNonNull(GraphQLString) },\n      },\n      resolve: (next, src, args, context) =\u003e {\n         // Implement your authentication logic\n         return next();\n      },\n   });\n   \n   module.exports = new GraphQLSchema({\n      directives: [authDirective],\n      types: [UserType],\n      query: new GraphQLObjectType({\n         name: 'RootQueryType',\n         fields: {\n            user: {\n               type: UserType,\n               resolve: (root, args, context) =\u003e {\n                  // Provide field values here\n               },\n               users: {\n                  type: new GraphQLList(UserType),\n                  auth: {\n                     requires: 'admin',\n                  },\n                  resolve: (root, args, context) =\u003e {\n                     // Provide field values here\n                  },\n               },\n            },\n         },\n      }),\n   });\n   ```\n\u003cbr\u003e\n\n## 6. Explain the concept of _fields_ in _GraphQL_.\n\n**Fields** form the basis of GraphQL data retrieval. Whereas REST often necessitates multiple endpoints, GraphQL consolidates this need into a single **query**.\n\nGraphQL representations are akin to objects, with each object possibly possessing numerous **fields**. This creates a hierarchy, especially useful when interacting with more complex datasets.\n\n### Basic Structure\n\nQueries consist of one or more fields. Each field can be an object, a scalar value, or an array of other objects or scalar values.\n\nStructurally, a **field** within a query resembles an object property in JavaScript or a dictionary entry in Python.\n\n### Self-Referring Objects\n\nFields can maintain a one-to-one mapping with backend resources. However, they can also **refer to themselves**. This self-reference is invaluable for processing hierarchical data structures.\n\nA simple example is a tree, where each node can potentially have multiple child nodes.\n\nGraphQL exploits self-referential fields to enable powerful data relationships, such as nodes having other nodes as their children. \n\n### Code Example: Simple Query\n\nHere is the JSON representation:\n\n```json\n\n{\n  \"query\": {\n    \"user\": {\n      \"id\": 123,\n      \"name\": \"John Doe\"\n    }\n  }\n}\n```\n\nAnd here is the corresponding algorithm:\n\n```javascript\nfunction fetchData(query) {\n  const result = {};\n  for (let field in query) {\n    if (isValidField(field)) {\n      result[field] = fetchData(query[field]);\n    }\n  }\n  return result;\n}\n```\n\n### Code Example: Self-Referring Queries\n\nHere are the JSON representation and the corresponding Python algorithm:\n\n```json\n\n{\n  \"query\": {\n    \"user\": {\n      \"id\": 123,\n      \"posts\": {\n        \"title\": \"GraphQL Basics\"\n      }\n    }\n  }\n}\n```\n\n```python\ndef fetch_user_data(user_id, query):\n    user_data = fetch_user_from_db(user_id)\n    result = {}\n\n    for field, value in user_data.items():\n        if field in query:\n            if isinstance(value, dict):\n                result[field] = fetch_user_data(user_id, query[field])\n            else:\n                result[field] = value\n\n    return result\n```\n\u003cbr\u003e\n\n## 7. How does _GraphQL_ handle _data types_?\n\n**GraphQL** brings a robust **type system** that ensures clear data structures and reliable schema enforcement. Let's take a closer look at key concepts like **Scalars**, **Enums**, and **Input Types**.\n\n### Types in GraphQL\n\n- **Scalar**: Represents a single value, such as a string or number.\n- **Object**: Defines a structured collection of fields, each with its type.\n- **List**: Indicates an array of values of the specified type.\n- **Enum**: Offers a predefined set of possible values.\n- **Union**: Represents a selection of object types, yet only allows querying common fields.\n- **Interface**: Guarantees certain fields on all possible implementing types.\n\n### Code Example: Basic Scalar and Object Types\n\nHere is Schema Definition Language (SDL):\n\n- For a scalar type\n\n```graphql\nscalar DateTime\n```\n\n- For an object type\n\n```graphql\ntype Author {\n  id: ID!\n  name: String\n  books: [Book]\n}\n```\n\nAnd here is the complete schema with Query and Mutation:\n\n```graphql\ntype Query {\n  author(id: ID!): Author\n  allAuthors: [Author]\n}\n\ntype Mutation {\n  addAuthor(name: String!): Author\n}\n\ntype Book {\n  title: String\n  author: Author\n}\n```\n\n### Code Example: Using Enums and Union Types\n\nHere is schema using Enums:\n\n```graphql\nenum Episode {\n  NEW_HOPE\n  EMPIRE\n  JEDI\n}\n\ntype Character {\n  name: String!\n  appearsIn: [Episode!]!\n}\n```\n\nAnd here is an example using Union Types:\n\n```graphql\ntype Human {\n  name: String!\n  height(unit: LengthUnit = METER): Float\n}\n\ntype Droid {\n  id: String!\n  name: String!\n}\n\nunion SearchResult = Human | Droid\n```\n\n### Code Example: Custom Input Types\n\nHere is a code example using **Scalars** and **Input Types**:\n\n- For a scalar input:\n\n```graphql\ninput DateRange {\n  start: DateTime\n  end: DateTime\n}\n```\n\n- For a custom input type:\n\n```graphql\ntype Query {\n  getPosts(publishedAfter: DateRange): [Post]\n}\n```\n\u003cbr\u003e\n\n## 8. In _GraphQL_, what are _queries_ and _mutations_?\n\nIn **GraphQL**, developers use two main types of operations to interact with data, known as **Queries** and **Mutations**.\n\n### Queries\n\n- **Purpose**: Read data from the server.\n- **HTTP Equivalent**: Usually `GET`.\n- **Immutability**: Queries are **Immutable**; they don't change server data.\n- **Requesting Specific Fields**: Allows clients to fetch only the data they need, increasing efficiency.\n- **Caching**: Results can be cached since queries remain consistent unless modified by the client.\n- **Errors**: Fails if the server cannot fulfill the data request.\n\n### Mutations\n\n- **Purpose**: Modify data on the server.\n- **HTTP Equivalent**: Typically `POST` or `PUT`.\n- **Immutability**: Mutations are **Mutable**; they trigger data changes.\n- **Requesting Specific Fields**: Can include a return payload of specific fields for client updates post-mutation.\n- **Caching**: Results are typically not cacheable.\n- **Errors**: Can indicate both successes and failures, and usually carry specific feedback.\n\u003cbr\u003e\n\n## 9. Describe how you would fetch data with a _GraphQL query_.\n\nWhen integrating **GraphQL**, data retrieval is performed through a query.\n\n### Steps for Fetching Data with a GraphQL Query\n\n1. **Define the Query**:\n    GraphQL queries specify the exact shape and structure of the expected response using the same dataset as the server schema.\n\n2. **Execute the Query**:\n    Queries are typically triggered via an HTTP POST request to the server's endpoint.\n\n3. **Handle the Response**:\n    Expect the exact data structure that you requested, with no need for subsequent requests or data manipulation.\terrors, and then receive the data in the precise shape you requested.\n\n### Example GraphQL Query\n\n```graphql\nquery {\n  bookById(id: \"4\") {\n    title\n    author {\n      name\n      age\n    }\n  }\n}\n```\n\u003cbr\u003e\n\n## 10. What are _scalar types_ in _GraphQL_?\n\n**GraphQL** augments traditional data modeling by incorporating its unique concept of **scalars**, which represent singular, atomic data types.\n\n### Core Scalars\n\n- **Int**: A signed 32-bit integer.\n- **Float**: A double-precision floating-point number.\n- **String**: A sequence of characters.\n\nThe **Boolean** type, representing true or false, is also one of the core scalars.\n\n### Custom Scalars\n\nDevelopers can define custom data types using **custom scalars** to match specific requirements. For instance, `Date` might be a developer-defined custom scalar that conforms to date-time values.\n\nGraphQL provides easy extensibility through custom scalars to cater to diverse data types not covered by its core set or to enforce data consistency.\n\n### Advantages\n\n- **Uniformity**: Scalars ensure consistent data representation across diverse clients.\n- **Ease of Extension**: Custom scalars let you unleash flexibility within GraphQL, tailoring data types to your unique needs.\n- **Efficiency**: Since each query selects precisely what's needed, reduced data transmission decreases loading time and conserves bandwidth.\n\u003cbr\u003e\n\n## 11. Explain the role of _resolvers_ in _GraphQL_.\n\n**Resolvers** in GraphQL tie specific fields of a schema to the actual functions that resolve these fields. They are critical for data fetching and manipulation.\n\n### Core Functions of Resolvers\n\n- **Data Fetching**: The primary role of resolvers is to fetch the data for the fields they are responsible for.\n- **Data Transformation**: Resolvers can perform any necessary transformations on the data before returning it to the client.\n- **Data Source Specification**: Resolvers detail where to retrieve the data from (such as a database or an API).\n\n### Resolver Structure\n\n- **Single Responsibility**: A resolver is responsible for a specific field in the schema.\n- **Parent-Child Relationships**: Resolvers can \"pass\" data between related fields, e.g., a user resolver can return details about a user's posts.\n\n### Resolver Types\n\n- **Root Resolvers**: Deal with top-level query and mutation fields.\n- **Nested Resolvers**: Handle specific fields on related types.\n\n### Code Example: Resolvers in GraphQL\n\nHere is the GraphQL Schema:\n\n```graphql\ntype Query {\n  user(id: Int!): User\n}\n\ntype User {\n  id: Int!\n  name: String!\n  posts: [Post]\n}\n\ntype Post {\n  id: Int!\n  title: String!\n  content: String!\n}\n```\n\nAnd here is the resolver code in JavaScript:\n\n```javascript\nconst resolvers = {\n  Query: {\n    user: (parent, { id }, context, info) =\u003e fetchUser(id),\n  },\n  User: {\n    posts: (parent, args, context, info) =\u003e fetchPostsForUser(parent.id),\n  },\n};\n\n// Sample data for illustration\nconst sampleData = {\n  users: [\n    { id: 1, name: \"John\" },\n    { id: 2, name: \"Jane\" },\n  ],\n  posts: [\n    { id: 1, title: \"First Post\", content: \"Hello, first post!\", userId: 1 },\n  ],\n};\n\nfunction fetchUser(id) {\n  return sampleData.users.find((user) =\u003e user.id === id);\n}\n\nfunction fetchPostsForUser(userId) {\n  return sampleData.posts.filter((post) =\u003e post.userId === userId);\n}\n```\n\nIn this example, when a client sends a query for a user's posts, the `posts` resolver is invoked and calls `fetchPostsForUser` to retrieve the posts associated with that user.\n\u003cbr\u003e\n\n## 12. What are the advantages of using _GraphQL_ over other API query languages?\n\n**GraphQL** offers many advantages over traditional REST APIs, ranging from optimized client-server communication to improved developer experience.\n\n### Advantages over REST\n\n#### Efficient Data Retrieval\n\n- **Selectivity**: GraphQL allows clients to specify the exact fields they need, reducing data over-fetching.\n- **No Multiple Endpoints**: Instead of hitting multiple endpoints for diverse data, clients can make a single request.\n\n#### Data Integrity\n\n- **Strongly Typed Schema**: GraphQL ensures data consistency by defining a schema, a feature not inherent in REST.\n- **Structured Endpoints**: REST APIs can alter data formats and required attributes, making assumptions about endpoint responses more error-prone.\n\n#### Client-Specific Data Shaping\n\n- **Client Needs Alignment**: GraphQL aligns server data with client requirements, promoting a more tailored approach for each client.\n\n#### Reduced Chatter\n\n- **Mitigated Under-Fetching**: REST can suffer from under-fetching, prompting multiple requests for comprehensive data.\n- **Streamlined Data Collection**: GraphQL, on the other hand, accesses interconnected entities and their data with one consolidated request.\n\n#### Real-Time Flexibility\n\n- **Socket-Like Experience**: Integrated subscriptions in GraphQL allow for real-time updates, a feature often necessitating additional effort in REST.\n\n### Advantages over Other Query Languages\n\n#### Multiple Data Sources\n\n- **Unified Backend**: With GraphQL, you can amalgamate data from various sources into a single endpoint, a setup that's more challenging with other languages like SQL.\n\n#### Ecosystem Integration\n\n- **Comprehensive API**: GraphQL has a robust toolset, including playgrounds that offer live interaction.\n- **Inherent Documentation**: Its introspective nature ensures self-documenting APIs, a feature often less prominent in other query languages.\n\n#### Post-Query Actions\n\n- **Control Over Response**: Clients have unparalleled influence over the response format, something less straightforward in languages like SQL.\n- **Data Manipulation**: With GraphQL, you can extrapolate data for specific tasks, going beyond the typical \"get\" operations.\n\n#### Embedded Domain Solutions\n\n- **Domain-Driven Applications**: GraphQL is effective in presenting the domain model to the user, enhancing user interaction and comprehension.\n\u003cbr\u003e\n\n## 13. How do you pass _arguments_ to _fields_ in _GraphQL queries_?\n\nIn GraphQL, **queries** represent requests for specific data fields. To refine these requests, you can use **arguments** with fields. \n\n### Syntax for Passing Arguments\n\nTo **pass arguments**, include them within the parentheses next to the field name. Each argument is defined using its unique name followed by the colon `:` and the intended value.\n\n#### Example: Retrieve a Specific User\n\n```graphql\n{\n  user(id: \"XYZ_123\") {\n    name\n    email\n  }\n}\n```\n\n### Code Example: Passing Arguments\n\nHere is the GraphQL schema:\n\n```graphql\ntype Query {\n  booksByAuthor(author: String, count: Int): [Book]\n}\n```\n\nAnd here is the query:\n\n```graphql\n{\n  booksByAuthor(author: \"JK Rowling\", count: 3) {\n    title\n  }\n}\n```\n\u003cbr\u003e\n\n## 14. What is a _fragment_ in _GraphQL_ and how are they used?\n\nIn **GraphQL**, a **fragment** enables describing a set of fields that can be repeatedly used across multiple queries.\n\n### Benefits of Fragments\n\n- **Reusability**: Easily reuse identical fields in various queries.\n- **Modularity**: Enhance code organization by separating logical groupings.\n- **Clarity**: Increase readability by outlining expected data needs in one place.\n\n### Fragment Definition and Reference\n\n#### Definition\n\nFragments are crafted using the `fragment` keyword and must specify a **name** along with the desired fields. They are scoped to a particular type.\n\n```graphql\nfragment UserInfo on User {\n  id\n  name\n  email\n}\n```\n\n#### Reference\n\nTo incorporate a fragment into a query, you utilize the `...` (spread) syntax followed by the fragment name.\n\n```graphql\nquery GetUserAndTheirPost {\n  user(id: \"123\") {\n    ...UserInfo\n  }\n  postsForUser(id: \"123\") {\n    ...PostInfo\n  }\n}\n```\n\n### Handling Duplicates\n\nWhile fragments help with code modularity and repeated field lists, GraphQL servers are smart enough to **deduplicate** and combine fields from all sources, ensuring minimal overhead in the underlying data fetch.\n\n### Multiple Fragments\n\nQueries can reference multiple fragments, and the fields from all fragments get composed in the query, streamlining data handling.\n\n```graphql\nquery GetMyData {\n  myself {\n    ...BasicUserInfo\n    ...ExtendedUserInfo\n    ...UserAddressInfo\n  }\n}\n```\n\n### Client-Specific Fragments\n\nSometimes, clients might have unique field requirements that the server's general schema doesn't cover. For this, client-specific fragments offer an avenue to define custom fields tailored to the client's needs.\n\n```graphql\nfragment DisplayUserInfo on User {\n  ... on RegularUser {\n    subscriptionStatus\n    lastLogin\n    securityQuestions\n  }\n  ... on AdminUser {\n    permissions\n    staffSince\n  }\n}\n```\n\nIn contrast to globally defined fragments, client-specific fragments cater to the specific needs of the query or operation where they're referenced.\n\u003cbr\u003e\n\n## 15. How does _GraphQL_ handle _caching_?\n\n**Data Federation** in GraphQL, achieved through resolvers, instigates caching at multiple levels to heighten efficiency and optimize data handling.\n\n### Caching Strategies\n\n#### Level 1: Client-Side Caching\n\n- **Purpose**: Minimize network traffic and local state management.\n- **Mechanism**: `Apollo Client` offers automatic in-memory caching. This ensures that redundant requests such as querying the same data multiple times don't hit the server.\n\n#### Level 2: Cloud-Controlled Caching\n\n- **Purpose**: Amplify efficiency by using explicitly stated HTTP caching directives.\n- **Mechanism**: The caching mechanism of the server is dependent on the HTTP cache-control headers. If data is cacheable, these headers specify how long it should be kept in the cache.\n\n#### Level 3: Persistent Caching\n\n- **Purpose**: Establish a global and persistent cache for recurrent data requests.\n- **Mechanism**: Beyond the scope of GraphQL per se, several solutions like Redis for in-memory caching or Apache Ignite as a distributed cache facilitate data storage, minimizing the need for repeated remote calls.\n\n### Multi-Level Cache Coherency\n\nGraphQL employs strategies to ensure coherence across the various cache levels:\n\n- **Real-Time Feed**: With subscriptions, a server can alert the client about new data, prompting cache updates.\n- **Partial Updates**: Through `GraphQL` subscriptions, you can tailor the response to only include changed or updated information, preventing a full cache refresh.\n- **Optimistic UI and cache updates**: `Apollo Client` manages client-side cache updates, providing immediate UI feedback. Updates are subsequently synched with the server, ensuring coherence.\n\n### Code Example: Caching Directives\n\nHere is the `GraphQL SDL` schema definitions:\n\n```graphql\ntype Query {\n  # Utilizes defaults from server config\n  getUser(id: ID!): User @cacheControl\n\n  # A specific request with an assigned cache time\n  getPost(id: ID!): Post @cacheControl(maxAge: 60)\n\n  # Bypasses cache directives\n  getMessage(id: ID!): Message @cacheControl(maxAge: 0)\n}\n\ntype User {\n  id: ID!\n  name: String!\n  email: String!\n}\n\ntype Post {\n  id: ID!\n  title: String!\n  content: String!\n}\n\ntype Message {\n  id: ID!\n  text: String!\n}\n\ndirective @cacheControl(\n  maxAge: Int\n  scope: CacheScope\n  inheritMaxAge: Boolean\n) on FIELD_DEFINITION | OBJECT | INTERFACE\n```\n\u003cbr\u003e\n\n\n\n#### Explore all 100 answers here 👉 [Devinterview.io - GraphQL](https://devinterview.io/questions/web-and-mobile-development/graphql-interview-questions)\n\n\u003cbr\u003e\n\n\u003ca href=\"https://devinterview.io/questions/web-and-mobile-development/\"\u003e\n\u003cimg src=\"https://firebasestorage.googleapis.com/v0/b/dev-stack-app.appspot.com/o/github-blog-img%2Fweb-and-mobile-development-github-img.jpg?alt=media\u0026token=1b5eeecc-c9fb-49f5-9e03-50cf2e309555\" alt=\"web-and-mobile-development\" width=\"100%\"\u003e\n\u003c/a\u003e\n\u003c/p\u003e\n\n","funding_links":[],"categories":[],"sub_categories":[],"project_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fdevinterview-io%2Fgraphql-interview-questions","html_url":"https://awesome.ecosyste.ms/projects/github.com%2Fdevinterview-io%2Fgraphql-interview-questions","lists_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fdevinterview-io%2Fgraphql-interview-questions/lists"}