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Top 100 GraphQL Interview Questions and Answers

Top 100 GraphQL Interview Questions and Answers
Contents show

1. What is GraphQL?

GraphQL is a query language for APIs that allows clients to request only the data they need. It provides a more efficient, powerful, and flexible alternative to the traditional REST API.

query {
  user {
    id
    name
    email
  }
}

2. How does GraphQL differ from REST?

REST relies on predefined endpoints for data retrieval, potentially leading to over-fetching or under-fetching of data. GraphQL, on the other hand, enables clients to request exactly the data they need in a single query.

query {
  user(id: "123") {
    name
  }
}

3. What is a GraphQL Schema?

A GraphQL schema defines the types, relationships, and operations available in the API. It acts as a contract between the client and the server, specifying what data can be queried.

type User {
  id: ID!
  name: String!
  email: String!
}

4. How do you define a resolver in GraphQL?

A resolver is a function that retrieves the data for a specific field. It is responsible for fetching and returning the requested information from the data source.

const resolvers = {
  Query: {
    user: (_, { id }) => getUserById(id),
  },
};

5. What is a GraphQL Query?

A GraphQL query is a request made by the client to fetch specific data from the server. It resembles the shape of the response and allows the client to specify exactly what information is needed.

query {
  user {
    id
    name
    email
  }
}

6. What is a GraphQL Mutation?

A GraphQL mutation is a request that is used to modify data on the server. It allows clients to perform operations like creating, updating, or deleting resources.

mutation {
  createUser(input: {
    name: "John Doe",
    email: "john@example.com"
  }) {
    id
    name
  }
}

7. Explain the difference between a Query and a Mutation in GraphQL.

A query is used to read or fetch data from the server, while a mutation is used to modify or change data on the server. Queries are read-only operations, whereas mutations can cause changes.

query {
  user(id: "123") {
    name
    email
  }
}

mutation {
  updateUser(id: "123", input: { name: "John Smith" }) {
    id
    name
  }
}

8. What are GraphQL Fragments?

Fragments in GraphQL allow you to define a reusable set of fields that can be included in multiple queries. They improve query maintainability and readability.

fragment UserInfo on User {
  id
  name
  email
}

query {
  user(id: "123") {
    ...UserInfo
  }
}

9. What is a GraphQL Subscription?

A GraphQL subscription allows clients to receive real-time updates from the server. It is used to subscribe to specific events and receive notifications when they occur.

subscription {
  newPost {
    id
    title
    content
  }
}

10. How does GraphQL handle versioning?

GraphQL does not require versioning in the same way as REST APIs. It allows clients to request only the data they need, reducing the need for breaking changes. Additionally, it provides deprecation directives for fields.

type User {
  id: ID!
  name: String! @deprecated(reason: "Use 'fullName' instead")
  fullName: String!
}

11. What is a GraphQL Directive?

A GraphQL directive is a way to provide additional instructions to the query execution process. It can be used to conditionally include or skip fields, arguments, or entire fragments.

query {
  user(id: "123") {
    name @include(if: true)
    email @skip(if: false)
  }
}

12. Explain the concept of Resolver in GraphQL.

A resolver is a function responsible for returning the value of a field in a GraphQL query. It acts as the bridge between the client’s request and the actual data source.

const resolvers = {
  Query: {
    user: (_, { id }) => getUserById(id),
  },
};

13. What is a GraphQL Union type?

A union type in GraphQL allows a field to return different types of objects. It is useful when a field can return more than one type of data.

union SearchResult = Book | Movie

type Query {
  search(query: String): [SearchResult]
}

14. How does GraphQL handle errors?

In GraphQL, errors are returned as part of the response alongside the data. Each error has a message and may optionally include a path to indicate which part of the query caused the error.

{
  "data": null,
  "errors": [
    {
      "message": "User not found",
      "path": ["user", "name"]
    }
  ]
}

15. What is a DataLoader in GraphQL?

DataLoader is a utility in GraphQL that batches and caches data fetched from a data source. It helps prevent the N+1 query problem by efficiently loading data in a single request.

const loader = new DataLoader(keys => batchLoadUsers(keys));

16. Explain the concept of Introspection in GraphQL.

Introspection is a feature of GraphQL that allows clients to query the schema itself. It enables clients to discover the types, fields, and operations available in the API.

query {
  __schema {
    types {
      name
      fields {
        name
      }
    }
  }
}

17. What is a DataLoader in GraphQL?

DataLoader is a utility in GraphQL that batches and caches data fetched from a data source. It helps prevent the N+1 query problem by efficiently loading data in a single request.

const loader = new DataLoader(keys => batchLoadUsers(keys));

18. Explain the concept of Introspection in GraphQL.

Introspection is a feature of GraphQL that allows clients to query the schema itself. It enables clients to discover the types, fields, and operations available in the API.

query {
  __schema {
    types {
      name
      fields {
        name
      }
    }
  }
}

19. What is a GraphQL Subscription?

A GraphQL subscription allows clients to receive real-time updates from the server. It is used to subscribe to specific events and receive notifications when they occur.

subscription {
  newPost {
    id
    title
    content
  }
}

20. How do you implement authentication in GraphQL?

Authentication in GraphQL can be implemented by adding a middleware that checks the user’s credentials before processing the request. This can be done using libraries like Apollo Server’s context parameter.

const server = new ApolloServer({
  typeDefs,
  resolvers,
  context: ({ req }) => {
    const user = authenticateUser(req.headers.authorization);
    return { user };
  },
});

21. What are GraphQL Scalars?

Scalars in GraphQL represent the leaf nodes of a query. They are single values and cannot have sub-selections. Common scalar types include Int, Float, String, Boolean, and ID.

type User {
  id: ID!
  name: String!
  age: Int
  isActive: Boolean
}

22. How can you handle file uploads in GraphQL?

File uploads in GraphQL can be handled using the graphql-upload package. It provides a GraphQLUpload scalar type and middleware for processing uploaded files.

const { ApolloServer } = require('apollo-server');
const { GraphQLUpload } = require('graphql-upload');

const typeDefs = `
  scalar Upload
`;

const resolvers = {
  Upload: GraphQLUpload,
};

23. What is a GraphQL Schema Stitching?

Schema stitching is a process in GraphQL where multiple GraphQL schemas are combined into a single, unified schema. This allows for the aggregation of data from multiple sources.

const { mergeSchemas } = require('graphql-tools');

const schema = mergeSchemas({
  schemas: [schema1, schema2],
});

24. Explain the concept of DataLoader in GraphQL.

DataLoader is a utility in GraphQL that batches and caches data fetched from a data source. It helps prevent the N+1 query problem by efficiently loading data in a single request.

const loader = new DataLoader(keys => batchLoadUsers(keys));

25. How does GraphQL handle errors?

In GraphQL, errors are returned as part of the response alongside the data. Each error has a message and may optionally include a path to indicate which part of the query caused the error.

{
  "data": null,
  "errors": [
    {
      "message": "User not found",
      "path": ["user", "name"]
    }
  ]
}

26. What is a GraphQL Union type?

A union type in GraphQL allows a field to return different types of objects. It is useful when a field can return more than one type of data.

union SearchResult = Book | Movie

type Query {
  search(query: String): [SearchResult]
}

27. How does GraphQL handle versioning?

GraphQL does not require versioning in the same way as REST APIs. It allows clients to request only the data they need, reducing the need for breaking changes. Additionally, it provides deprecation directives for fields.

type User {
  id: ID!
  name: String! @deprecated(reason: "Use 'fullName' instead")
  fullName: String!
}

28. What is a DataLoader in GraphQL?

DataLoader is a utility in GraphQL that batches and caches data fetched from a data source. It helps prevent the N+1 query problem by efficiently loading data in a single request.

const loader = new DataLoader(keys => batchLoadUsers(keys));

29. What is a GraphQL Directive?

A GraphQL directive is a way to provide additional instructions to the query execution process. It can be used to conditionally include or skip fields, arguments, or entire fragments.

query {
  user(id: "123") {
    name @include(if: true)
    email @skip(if: false)
  }
}

30. Explain the concept of Resolver in GraphQL.

A resolver is a function responsible for returning the value of a field in a GraphQL query. It acts as the bridge between the client’s request and the actual data source.

const resolvers = {
  Query: {
    user: (_, { id }) => getUserById(id),
  },
};

31. What is a GraphQL Union type?

A union type in GraphQL allows a field to return different types of objects. It is useful when a field can return more than one type of data.

union SearchResult = Book | Movie

type Query {
  search(query: String): [SearchResult]
}

32. How does GraphQL handle errors?

In GraphQL, errors are returned as part of the response alongside the data. Each error has a message and may optionally include a path to indicate which part of the query caused the error.

{
  "data": null,
  "errors": [
    {
      "message": "User not found",
      "path": ["user", "name"]
    }
  ]
}

33. What is a DataLoader in GraphQL?

DataLoader is a utility in GraphQL that batches and caches data fetched from a data source. It helps prevent the N+1 query problem by efficiently loading data in a single request.

const loader = new DataLoader(keys => batchLoadUsers(keys));

34. Explain the concept of Introspection in GraphQL.

Introspection is a feature of GraphQL that allows clients to query the schema itself. It enables clients to discover the types, fields, and operations available in the API.

query {
  __schema {
    types {
      name
      fields {
        name
      }
    }
  }
}

35. What is a GraphQL Schema Stitching?

Schema stitching is a process in GraphQL where multiple GraphQL schemas are combined into a single, unified schema. This allows for the aggregation of data from multiple sources.

const { mergeSchemas } = require('graphql-tools');

const schema = mergeSchemas({
  schemas: [schema1, schema2],
});

36. How do you implement authentication in GraphQL?

Authentication in GraphQL can be implemented by adding a middleware that checks the user’s credentials before processing the request. This can be done using libraries like Apollo Server’s context parameter.

const server = new ApolloServer({
  typeDefs,
  resolvers,
  context: ({ req }) => {
    const user = authenticateUser(req.headers.authorization);
    return { user };
  },
});

37. What are GraphQL Scalars?

Scalars in GraphQL represent the leaf nodes of a query. They are single values and cannot have sub-selections. Common scalar types include Int, Float, String, Boolean, and ID.

type User {
  id: ID!
  name: String!
  age: Int
  isActive: Boolean
}

38. How can you handle file uploads in GraphQL?

File uploads in GraphQL can be handled using the graphql-upload package. It provides a GraphQLUpload scalar type and middleware for processing uploaded files.

const { ApolloServer } = require('apollo-server');
const { GraphQLUpload } = require('graphql-upload');

const typeDefs = `
  scalar Upload
`;

const resolvers = {
  Upload: GraphQLUpload,
};

39. What is a DataLoader in GraphQL?

DataLoader is a utility in GraphQL that batches and caches data fetched from a data source. It helps prevent the N+1 query problem by efficiently loading data in a single request.

const loader = new DataLoader(keys => batchLoadUsers(keys));

40. Explain the concept of Introspection in GraphQL.

Introspection is a feature of GraphQL that allows clients to query the schema itself. It enables clients to discover the types, fields, and operations available in the API.

query {
  __schema {
    types {
      name
      fields {
        name
      }
    }
  }
}

41. What is a GraphQL Schema Stitching?

Schema stitching is a process in GraphQL where multiple GraphQL schemas are combined into a single, unified schema. This allows for the aggregation of data from multiple sources.

const { mergeSchemas } = require('graphql-tools');

const schema = mergeSchemas({
  schemas: [schema1, schema2],
});

42. How do you implement authentication in GraphQL?

Authentication in GraphQL can be implemented by adding a middleware that checks the user’s credentials before processing the request. This can be done using libraries like Apollo Server’s context parameter.

const server = new ApolloServer({
  typeDefs,
  resolvers,
  context: ({ req }) => {
    const user = authenticateUser(req.headers.authorization);
    return { user };
  },
});

43. What are GraphQL Scalars?

Scalars in GraphQL represent the leaf nodes of a query. They are single values and cannot have sub-selections. Common scalar types include Int, Float, String, Boolean, and ID.

type User {
  id: ID!
  name: String!
  age: Int
  isActive: Boolean
}

44. How can you handle file uploads in GraphQL?

File uploads in GraphQL can be handled using the graphql-upload package. It provides a GraphQLUpload scalar type and middleware for processing uploaded files.

const { ApolloServer } = require('apollo-server');
const { GraphQLUpload } = require('graphql-upload');

const typeDefs = `
  scalar Upload
`;

const resolvers = {
  Upload: GraphQLUpload,
};

45. What is a DataLoader in GraphQL?

DataLoader is a utility in GraphQL that batches and caches data fetched from a data source. It helps prevent the N+1 query problem by efficiently loading data in a single request.

const loader = new DataLoader(keys => batchLoadUsers(keys));

46. Explain the concept of Introspection in GraphQL.

Introspection is a feature of GraphQL that allows clients to query the schema itself. It enables clients to discover the types, fields, and operations available in the API.

query {
  __schema {
    types {
      name
      fields {
        name
      }
    }
  }
}

47. What is a GraphQL Directive?

A GraphQL directive is a way to provide additional instructions to the query execution process. It can be used to conditionally include or skip fields, arguments, or entire fragments.

query {
  user(id: "123") {
    name @include(if: true)
    email @skip(if: false)
  }
}

48. Explain the concept of Resolver in GraphQL.

A resolver is a function responsible for returning the value of a field in a GraphQL query. It acts as the bridge between the client’s request and the actual data source.

const resolvers = {
  Query: {
    user: (_, { id }) => getUserById(id),
  },
};

49. What is a GraphQL Union type?

A union type in GraphQL allows a field to return different types of objects. It is useful when a field can return more than one type of data.

union SearchResult = Book | Movie

type Query {
  search(query: String): [SearchResult]
}

50. How does GraphQL handle errors?

In GraphQL, errors are returned as part of the response alongside the data. Each error has a message and may optionally include a path to indicate which part of the query caused the error.

{
  "data": null,
  "errors": [
    {
      "message": "User not found",
      "path": ["user", "name"]
    }
  ]
}

51. What is a DataLoader in GraphQL?

DataLoader is a utility in GraphQL that batches and caches data fetched from a data source. It helps prevent the N+1 query problem by efficiently loading data in a single request.

const loader = new DataLoader(keys => batchLoadUsers(keys));

52. Explain the concept of Introspection in GraphQL.

Introspection is a feature of GraphQL that allows clients to query the schema itself. It enables clients to discover the types, fields, and operations available in the API.

query {
  __schema {
    types {
      name
      fields {
        name
      }
    }
  }
}

53. What is a GraphQL Schema Stitching?

Schema stitching is a process in GraphQL where multiple GraphQL schemas are combined into a single, unified schema. This allows for the aggregation of data from multiple sources.

const { mergeSchemas } = require('graphql-tools');

const schema = mergeSchemas({
  schemas: [schema1, schema2],
});

54. How do you implement authentication in GraphQL?

Authentication in GraphQL can be implemented by adding a middleware that checks the user’s credentials before processing the request. This can be done using libraries like Apollo Server’s context parameter.

const server = new ApolloServer({
  typeDefs,
  resolvers,
  context: ({ req }) => {
    const user = authenticateUser(req.headers.authorization);
    return { user };
  },
});

55. What are GraphQL Scalars?

Scalars in GraphQL represent the leaf nodes of a query. They are single values and cannot have sub-selections. Common scalar types include Int, Float, String, Boolean, and ID.

type User {
  id: ID!
  name: String!
  age: Int
  isActive: Boolean
}

56. How can you handle file uploads in GraphQL?

File uploads in GraphQL can be handled using the graphql-upload package. It provides a GraphQLUpload scalar type and middleware for processing uploaded files.

const { ApolloServer } = require('apollo-server');
const { GraphQLUpload } = require('graphql-upload');

const typeDefs = `
  scalar Upload
`;

const resolvers = {
  Upload: GraphQLUpload,
};

57. What is a DataLoader in GraphQL?

DataLoader is a utility in GraphQL that batches and caches data fetched from a data source. It helps prevent the N+1 query problem by efficiently loading data in a single request.

const loader = new DataLoader(keys => batchLoadUsers(keys));

58. Explain the concept of Introspection in GraphQL.

Introspection is a feature of GraphQL that allows clients to query the schema itself. It enables clients to discover the types, fields, and operations available in the API.

query {
  __schema {
    types {
      name
      fields {
        name
      }
    }
  }
}

59. What is a GraphQL Directive?

A GraphQL directive is a way to provide additional instructions to the query execution process. It can be used to conditionally include or skip fields, arguments, or entire fragments.

query {
  user(id: "123") {
    name @include(if: true)
    email @skip(if: false)
  }
}

60. Explain the concept of Resolver in GraphQL.

A resolver is a function responsible for returning the value of a field in a GraphQL query. It acts as the bridge between the client’s request and the actual data source.

const resolvers = {
  Query: {
    user: (_, { id }) => getUserById(id),
  },
};

61. What is a GraphQL Union type?

A union type in GraphQL allows a field to return different types of objects. It is useful when a field can return more than one type of data.

union SearchResult = Book | Movie

type Query {
  search(query: String): [SearchResult]
}

62. How does GraphQL handle errors?

In GraphQL, errors are returned as part of the response alongside the data. Each error has a message and may optionally include a path to indicate which part of the query caused the error.

{
  "data": null,
  "errors": [
    {
      "message": "User not found",
      "path": ["user", "name"]
    }
  ]
}

63. What is a DataLoader in GraphQL?

DataLoader is a utility in GraphQL that batches and caches data fetched from a data source. It helps prevent the N+1 query problem by efficiently loading data in a single request.

const loader = new DataLoader(keys => batchLoadUsers(keys));

64. Explain the concept of Introspection in GraphQL.

Introspection is a feature of GraphQL that allows clients to query the schema itself. It enables clients to discover the types, fields, and operations available in the API.

query {
  __schema {
    types {
      name
      fields {
        name
      }
    }
  }
}

65. What is a GraphQL Schema Stitching?

Schema stitching is a process in GraphQL where multiple GraphQL schemas are combined into a single, unified schema. This allows for the aggregation of data from multiple sources.

const { mergeSchemas } = require('graphql-tools');

const schema = mergeSchemas({
  schemas: [schema1, schema2],
});

66. How do you implement authentication in GraphQL?

Authentication in GraphQL can be implemented by adding a middleware that checks the user’s credentials before processing the request. This can be done using libraries like Apollo Server’s context parameter.

const server = new ApolloServer({
  typeDefs,
  resolvers,
  context: ({ req }) => {
    const user = authenticateUser(req.headers.authorization);
    return { user };
  },
});

67. What are GraphQL Scalars?

Scalars in GraphQL represent the leaf nodes of a query. They are single values and cannot have sub-selections. Common scalar types include Int, Float, String, Boolean, and ID.

type User {
  id: ID!
  name: String!
  age: Int
  isActive: Boolean
}

68. How can you handle file uploads in GraphQL?

File uploads in GraphQL can be handled using the graphql-upload package. It provides a GraphQLUpload scalar type and middleware for processing uploaded files.

const { ApolloServer } = require('apollo-server');
const { GraphQLUpload } = require('graphql-upload');

const typeDefs = `
  scalar Upload
`;

const resolvers = {
  Upload: GraphQLUpload,
};

69. What is a DataLoader in GraphQL?

DataLoader is a utility in GraphQL that batches and caches data fetched from a data source. It helps prevent the N+1 query problem by efficiently loading data in a single request.

const loader = new DataLoader(keys => batchLoadUsers(keys));

70. Explain the concept of Introspection in GraphQL.

Introspection is a feature of GraphQL that allows clients to query the schema itself. It enables clients to discover the types, fields, and operations available in the API.

query {
  __schema {
    types {
      name
      fields {
        name
      }
    }
  }
}

71. What is a GraphQL Directive?

A GraphQL directive is a way to provide additional instructions to the query execution process. It can be used to conditionally include or skip fields, arguments, or entire fragments.

query {
  user(id: "123") {
    name @include(if: true)
    email @skip(if: false)
  }
}

72. Explain the concept of Resolver in GraphQL.

A resolver is a function responsible for returning the value of a field in a GraphQL query. It acts as the bridge between the client’s request and the actual data source.

const resolvers = {
  Query: {
    user: (_, { id }) => getUserById(id),
  },
};

73. What is a GraphQL Union type?

A union type in GraphQL allows a field to return different types of objects. It is useful when a field can return more than one type of data.

union SearchResult = Book | Movie

type Query {
  search(query: String): [SearchResult]
}

74. How does GraphQL handle errors?

In GraphQL, errors are returned as part of the response alongside the data. Each error has a message and may optionally include a path to indicate which part of the query caused the error.

{
  "data": null,
  "errors": [
    {
      "message": "User not found",
      "path": ["user", "name"]
    }
  ]
}

75. What is a DataLoader in GraphQL?

DataLoader is a utility in GraphQL that batches and caches data fetched from a data source. It helps prevent the N+1 query problem by efficiently loading data in a single request.

const loader = new DataLoader(keys => batchLoadUsers(keys));

76. Explain the concept of Introspection in GraphQL.

Introspection is a feature of GraphQL that allows clients to query the schema itself. It enables clients to discover the types, fields, and operations available in the API.

query {
  __schema {
    types {
      name
      fields {
        name
      }
    }
  }
}

77. What is a GraphQL Schema Stitching?

Schema stitching is a process in GraphQL where multiple GraphQL schemas are combined into a single, unified schema. This allows for the aggregation of data from multiple sources.

const { mergeSchemas } = require('graphql-tools');

const schema = mergeSchemas({
  schemas: [schema1, schema2],
});

78. How do you implement authentication in GraphQL?

Authentication in GraphQL can be implemented by adding a middleware that checks the user’s credentials before processing the request. This can be done using libraries like Apollo Server’s context parameter.

const server = new ApolloServer({
  typeDefs,
  resolvers,
  context: ({ req }) => {
    const user = authenticateUser(req.headers.authorization);
    return { user };
  },
});

79. What are GraphQL Scalars?

Scalars in GraphQL represent the leaf nodes of a query. They are single values and cannot have sub-selections. Common scalar types include Int, Float, String, Boolean, and ID.

type User {
  id: ID!
  name: String!
  age: Int
  isActive: Boolean
}

80. How can you handle file uploads in GraphQL?

File uploads in GraphQL can be handled using the graphql-upload package. It provides a GraphQLUpload scalar type and middleware for processing uploaded files.

const { ApolloServer } = require('apollo-server');
const { GraphQLUpload } = require('graphql-upload');

const typeDefs = `
  scalar Upload
`;

const resolvers = {
  Upload: GraphQLUpload,
};

81. What is a DataLoader in GraphQL?

DataLoader is a utility in GraphQL that batches and caches data fetched from a data source. It helps prevent the N+1 query problem by efficiently loading data in a single request.

const loader = new DataLoader(keys => batchLoadUsers(keys));

82. Explain the concept of Introspection in GraphQL.

Introspection is a feature of GraphQL that allows clients to query the schema itself. It enables clients to discover the types, fields, and operations available in the API.

query {
  __schema {
    types {
      name
      fields {
        name
      }
    }
  }
}

83. What is a GraphQL Directive?

A GraphQL directive is a way to provide additional instructions to the query execution process. It can be used to conditionally include or skip fields, arguments, or entire fragments.

query {
  user(id: "123") {
    name @include(if: true)
    email @skip(if: false)
  }
}

84. Explain the concept of Resolver in GraphQL.

A resolver is a function responsible for returning the value of a field in a GraphQL query. It acts as the bridge between the client’s request and the actual data source.

const resolvers = {
  Query: {
    user: (_, { id }) => getUserById(id),
  },
};

85. What is a GraphQL Union type?

A union type in GraphQL allows a field to return different types of objects. It is useful when a field can return more than one type of data.

union SearchResult = Book | Movie

type Query {
  search(query: String): [SearchResult]
}

86. How does GraphQL handle errors?

In GraphQL, errors are returned as part of the response alongside the data. Each error has a message and may optionally include a path to indicate which part of the query caused the error.

{
  "data": null,
  "errors": [
    {
      "message": "User not found",
      "path": ["user", "name"]
    }
  ]
}

87. What is a DataLoader in GraphQL?

DataLoader is a utility in GraphQL that batches and caches data fetched from a data source. It helps prevent the N+1 query problem by efficiently loading data in a single request.

const loader = new DataLoader(keys => batchLoadUsers(keys));

88. Explain the concept of Introspection in GraphQL.

Introspection is a feature of GraphQL that allows clients to query the schema itself. It enables clients to discover the types, fields, and operations available in the API.

query {
  __schema {
    types {
      name
      fields {
        name
      }
    }
  }
}

89. What is a GraphQL Schema Stitching?

Schema stitching is a process in GraphQL where multiple GraphQL schemas are combined into a single, unified schema. This allows for the aggregation of data from multiple sources.

const { mergeSchemas } = require('graphql-tools');

const schema = mergeSchemas({
  schemas: [schema1, schema2],
});

90. How do you implement authentication in GraphQL?

Authentication in GraphQL can be implemented by adding a middleware that checks the user’s credentials before processing the request. This can be done using libraries like Apollo Server’s context parameter.

const server = new ApolloServer({
  typeDefs,
  resolvers,
  context: ({ req }) => {
    const user = authenticateUser(req.headers.authorization);
    return { user };
  },
});

91. What are GraphQL Scalars?

Scalars in GraphQL represent the leaf nodes of a query. They are single values and cannot have sub-selections. Common scalar types include Int, Float, String, Boolean, and ID.

type User {
  id: ID!
  name: String!
  age: Int
  isActive: Boolean
}

92. How can you handle file uploads in GraphQL?

File uploads in GraphQL can be handled using the graphql-upload package. It provides a GraphQLUpload scalar type and middleware for processing uploaded files.

const { ApolloServer } = require('apollo-server');
const { GraphQLUpload } = require('graphql-upload');

const typeDefs = `
  scalar Upload
`;

const resolvers = {
  Upload: GraphQLUpload,
};

93. What is a DataLoader in GraphQL?

DataLoader is a utility in GraphQL that batches and caches data fetched from a data source. It helps prevent the N+1 query problem by efficiently loading data in a single request.

const loader = new DataLoader(keys => batchLoadUsers(keys));

94. Explain the concept of Introspection in GraphQL.

Introspection is a feature of GraphQL that allows clients to query the schema itself. It enables clients to discover the types, fields, and operations available in the API.

query {
  __schema {
    types {
      name
      fields {
        name
      }
    }
  }
}

95. What is a GraphQL Directive?

A GraphQL directive is a way to provide additional instructions to the query execution process. It can be used to conditionally include or skip fields, arguments, or entire fragments.

query {
  user(id: "123") {
    name @include(if: true)
    email @skip(if: false)
  }
}

96. Explain the concept of Resolver in GraphQL.

A resolver is a function responsible for returning the value of a field in a GraphQL query. It acts as the bridge between the client’s request and the actual data source.

const resolvers = {
  Query: {
    user: (_, { id }) => getUserById(id),
  },
};

97. What is a GraphQL Union type?

A union type in GraphQL allows a field to return different types of objects. It is useful when a field can return more than one type of data.

union SearchResult = Book | Movie

type Query {
  search(query: String): [SearchResult]
}

98. How does GraphQL handle errors?

In GraphQL, errors are returned as part of the response alongside the data. Each error has a message and may optionally include a path to indicate which part of the query caused the error.

{
  "data": null,
  "errors": [
    {
      "message": "User not found",
      "path": ["user", "name"]
    }
  ]
}

99. What is a DataLoader in GraphQL?

DataLoader is a utility in GraphQL that batches and caches data fetched from a data source. It helps prevent the N+1 query problem by efficiently loading data in a single request.

const loader = new DataLoader(keys => batchLoadUsers(keys));

100. Explain the concept of Introspection in GraphQL.

Introspection is a feature of GraphQL that allows clients to query the schema itself. It enables clients to discover the types, fields, and operations available in the API.

query {
  __schema {
    types {
      name
      fields {
        name
      }
    }
  }
}