面试题与答案

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.