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.