writeQuery

writeQuery is a function provided by the Apollo Client library. It is used to write data to the Apollo Client cache. This function allows developers to directly update the cache with new or modified data, which can be useful for various scenarios, such as optimistic updates or manually managing cache state.

The writeQuery function takes two primary arguments: a query object and a data object. The query object defines the structure and fields of the data that you intend to write, mirroring the structure of a GraphQL query. The data object contains the actual data that will be written into the cache, conforming to the shape specified by the query.

When writeQuery is called, Apollo Client attempts to match the provided query against existing data in the cache. If a match is found, the data is merged or replaced according to the query and data provided. This operation is synchronous and directly modifies the client-side cache.

Common use cases for writeQuery include implementing optimistic UI updates, where the cache is updated immediately to reflect a user's action before the server response is received. It can also be used to populate the cache with data fetched from non-GraphQL sources or to manually refetch and update specific parts of the cache after certain mutations or operations. It's a powerful tool for fine-grained control over the Apollo Client cache.