面试题与答案

GraphQL is a query language that allows clients to request the specific data they need, while REST is an architectural style that uses predefined endpoints to expose data. GraphQL provides more flexibility and efficiency in fetching data compared to REST.

A GraphQL schema defines the types of data that can be queried and the relationships between them. Types represent the shape of the data, and the schema serves as a contract between the client and the server regarding the structure of the API.

Fragments in GraphQL allow you to define reusable sets of fields that can be included in multiple queries. They help in avoiding duplication of field definitions and make queries more modular.

A query is used to fetch data from the server, while a mutation is used to modify data on the server. Queries are read-only operations, and mutations are used for any operation that causes a change in the data.

Directives in GraphQL are used to modify the behavior of a field or an entire query. They provide a way to conditionally include or skip fields, apply transformations, and control the execution of a query.

The `context` object in GraphQL resolvers is used to share contextual information, such as authentication details or database connections, among different parts of the application. It is often passed as an argument to resolvers.

GraphQL allows the use of forward and backward references in a schema, but circular dependencies can be resolved using lazy loading or by using the `GraphQLObjectType` constructor to create types that reference each other.

A union type in GraphQL allows a field to return different types of objects. It is useful when a field can have multiple types, and the client needs to handle each type differently.

The `@deprecated` directive in GraphQL is used to mark a field or enum value as deprecated. It provides information to clients about the deprecation and suggests an alternative field or value to use.

The `fragment` keyword in GraphQL is used to define reusable sets of fields that can be included in queries. Fragments help in organizing and reusing common field selections across multiple queries.

The `fetchPolicy` option in Apollo Client allows developers to control how queries are fetched and updated. It provides options like 'cache-first,' 'network-only,' and 'no-cache' to customize the caching behavior.

A schema in GraphQL is a collection of types that define the structure of the API. Types, on the other hand, represent the shape of the data, including scalar types, object types, and custom types defined in the schema.

The `alias` feature in GraphQL allows clients to rename the result of a field in the response. It is useful when multiple fields in a query have the same name or when clients want to provide a different name for clarity.