面试题与答案

GraphQL is a query language for APIs and a runtime environment for executing those queries with existing data. It allows clients to request only the data they need and nothing more.

A mutation is a GraphQL operation used to modify data on the server. It is similar to a query but is used for actions that cause a change in the data, such as creating, updating, or deleting records.

GraphQL allows clients to request only the data they need, reducing over-fetching and under-fetching issues. It provides a single endpoint for all data operations, enabling more efficient and flexible data fetching.

A scalar type in GraphQL represents a single value, such as a string, integer, boolean, or float. GraphQL provides a set of predefined scalar types, and custom scalar types can be defined as needed.

GraphQL avoids versioning by allowing clients to specify the exact shape of the response they need. This flexibility prevents breaking changes, as clients can evolve independently without relying on specific API versions.

A schema in GraphQL defines the types of data that can be queried and the relationships between them. It serves as a contract between the client and the server, specifying the structure of the API.

The `!` in GraphQL type definitions indicates that a field is non-nullable, meaning it must always have a value. It is used to express the presence of required data.

In GraphQL, null values are used to represent the absence of a value for a field. Fields can be explicitly marked as nullable or non-nullable using the `!` (exclamation mark) in the type definition.

GraphQL addresses over-fetching by allowing clients to specify the exact data they need. It mitigates under-fetching by enabling clients to request additional fields as needed, avoiding multiple round trips for data fetching.

GraphQL responses include an 'errors' field that contains an array of error objects if any errors occur during the execution of the query or mutation. This allows clients to handle errors gracefully.

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.

A resolver is a function that determines how to fetch the requested data. It is responsible for resolving the data from the server's data sources and returning it to the client. Resolvers are defined for each field in a GraphQL schema.

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

A subscription in GraphQL allows clients to receive real-time updates from the server. It is used for scenarios where the server can push data to the client when certain events occur, providing a mechanism for real-time communication.

Batching in GraphQL involves combining multiple queries or mutations into a single request to the server. This helps in reducing the number of network requests and improving the overall efficiency of data fetching.

The `__typename` field in GraphQL is automatically included in every object type and represents the name of the type. It is useful for client-side caching and identifying the type of an object in a polymorphic relationship.

To mitigate security concerns, GraphQL implementations often include features like query complexity analysis and depth limiting. These measures prevent overly complex or deep queries that could lead to denial-of-service attacks.

DataLoader is a utility in GraphQL that helps in batching and caching database queries. It is commonly used to address the N+1 query problem by efficiently loading data in batches.

Persisted queries involve storing the query on the server and sending a reference (hash) instead of the full query in client requests. This can reduce the payload size and enhance security by preventing injection attacks.

Batching in GraphQL involves combining multiple queries or mutations into a single request to the server. This helps in reducing the number of network requests and improving the overall efficiency of data fetching.