MissingQueryFunctionError class final

Thrown when a query is fetched with no query function anywhere in its options chain.

Never retried, whatever the retry policy says: the fetch settles in error after its one attempt, so the message is seen at once rather than after the full backoff.

Typical causes: a QueryClient.query whose options have no queryFn and whose key has no default one, or a refetch of a key that only ever had data written with setQueryData while no observer supplies a function. Give the options a queryFn, or register one for the key with QueryClient.setQueryDefaults.