QueryObserver

Defined in: packages/query-core/src/queryObserver.ts:56

A QueryObserver watches a single query in the QueryCache and computes a QueryObserverResult from its state, recomputing and notifying subscribers whenever the underlying query (or the observer's options) changes. It is the primitive that framework adapters (e.g. useQuery) build their hooks on top of, but it can also be used directly to observe and switch between queries outside of any framework.

Example#

const observer = new QueryObserver(queryClient, {
  queryKey: ['posts'],
  queryFn: fetchPosts,
})

const unsubscribe = observer.subscribe((result) => {
  console.log(result.data)
})

Extends#

• Subscribable<QueryObserverListener<TData, TError>>

Extended by#

• InfiniteQueryObserver

Type Parameters#

TQueryFnData#

TQueryFnData = unknown

TError#

TError = DefaultError

TData#

TData = TQueryFnData

TQueryData#

TQueryData = TQueryFnData

TQueryKey#

TQueryKey extends QueryKey = QueryKey

Constructors#

Constructor#

new QueryObserver<TQueryFnData, TError, TData, TQueryData, TQueryKey>(client: QueryClient, options: QueryObserverOptions<TQueryFnData, TError, TData, TQueryData, TQueryKey>): QueryObserver<TQueryFnData, TError, TData, TQueryData, TQueryKey>;

Defined in: packages/query-core/src/queryObserver.ts:86

Parameters#

client#

QueryClient

options#

QueryObserverOptions<TQueryFnData, TError, TData, TQueryData, TQueryKey>

Returns#

QueryObserver<TQueryFnData, TError, TData, TQueryData, TQueryKey>

Overrides#

Subscribable<QueryObserverListener<TData, TError>>.constructor

Properties#

options#

options: QueryObserverOptions<TQueryFnData, TError, TData, TQueryData, TQueryKey>;

Defined in: packages/query-core/src/queryObserver.ts:88

Methods#

destroy()#

destroy(): void;

Defined in: packages/query-core/src/queryObserver.ts:162

Stops observing the current query: clears all listeners, cancels the stale and refetch-interval timers, and removes this observer from the query it was observing.

Returns#

void

fetchOptimistic()#

fetchOptimistic(options: QueryObserverOptions<TQueryFnData, TError, TData, TQueryData, TQueryKey>): Promise<QueryObserverResult<TData, TError>>;

Defined in: packages/query-core/src/queryObserver.ts:407

Fetches a query defined by the given options without affecting this observer's own tracked query or result, and returns a promise that resolves with the QueryObserverResult for that fetch. This is useful for prefetching data that another observer (e.g. a query about to be navigated to) will need, ahead of time.

Parameters#

options#

QueryObserverOptions<TQueryFnData, TError, TData, TQueryData, TQueryKey>

The observer options of the query to fetch.

Returns#

Promise<QueryObserverResult<TData, TError>>

A promise that resolves with the result for the fetched query.

Example#

const result = await observer.fetchOptimistic({
  queryKey: ['posts', 2],
  queryFn: () => fetchPost(2),
})
console.log(result.data)

getCurrentQuery()#

getCurrentQuery(): Query<TQueryFnData, TError, TQueryData, TQueryKey>;

Defined in: packages/query-core/src/queryObserver.ts:366

Returns the Query instance this observer is currently observing.

Returns#

Query<TQueryFnData, TError, TQueryData, TQueryKey>

The observed query.

getCurrentResult()#

getCurrentResult(): QueryObserverResult<TData, TError>;

Defined in: packages/query-core/src/queryObserver.ts:325

Returns the most recently computed QueryObserverResult for the observed query. This is a point-in-time read; to be notified of updates as they happen, subscribe to the observer instead (its inherited subscribe method).

Returns#

QueryObserverResult<TData, TError>

The current result.

Example#

const result = observer.getCurrentResult()
console.log(result.status, result.data)

getOptimisticResult()#

getOptimisticResult(options: DefaultedQueryObserverOptions<TQueryFnData, TError, TData, TQueryData, TQueryKey>): QueryObserverResult<TData, TError>;

Defined in: packages/query-core/src/queryObserver.ts:276

Computes the result the observer would produce for the given (already-defaulted) options right now, building the underlying Query if it doesn't exist yet, without waiting for a subscription callback. Called by framework adapters on every render (e.g. useQuery) so the returned value is available synchronously, ahead of setOptions triggering an actual fetch.

Parameters#

options#

DefaultedQueryObserverOptions<TQueryFnData, TError, TData, TQueryData, TQueryKey>

The defaulted observer options to compute the result for.

Returns#

QueryObserverResult<TData, TError>

The result for the given options.

hasListeners()#

hasListeners(): boolean;

Defined in: packages/query-core/src/subscribable.ts:43

Returns true while at least one listener is registered, false once they have all unsubscribed.

Returns#

boolean

true if at least one listener is registered.

Inherited from#

Subscribable.hasListeners

refetch()#

refetch(options: RefetchOptions): Promise<QueryObserverResult<TData, TError>>;

Defined in: packages/query-core/src/queryObserver.ts:382

Refetches the observed query and returns a promise that resolves with the resulting QueryObserverResult.

Parameters#

options#

RefetchOptions = {}

Set cancelRefetch to false to keep a running fetch instead of cancelling it, and throwOnError to true to reject when the refetch fails.

Returns#

Promise<QueryObserverResult<TData, TError>>

A promise that resolves with the result after the refetch.

Example#

const result = await observer.refetch({ cancelRefetch: false })
console.log(result.data)

setOptions()#

setOptions(options: QueryObserverOptions<TQueryFnData, TError, TData, TQueryData, TQueryKey>): void;

Defined in: packages/query-core/src/queryObserver.ts:184

Updates the observer's options. This will re-resolve the query being observed (switching to a different query if the queryKey changed), trigger a fetch if the new options require one and the observer has subscribers, recompute the current result, and reschedule the stale and refetch-interval timers as needed.

Parameters#

options#

QueryObserverOptions<TQueryFnData, TError, TData, TQueryData, TQueryKey>

The new observer options. They are defaulted with QueryClient#defaultQueryOptions before being applied.

Returns#

void

Example#

observer.setOptions({ queryKey: ['posts', 1], queryFn: () => fetchPost(1) })
// later: switch to a different query, reusing the same observer
observer.setOptions({ queryKey: ['posts', 2], queryFn: () => fetchPost(2) })

shouldFetchOnReconnect()#

shouldFetchOnReconnect(): boolean;

Defined in: packages/query-core/src/queryObserver.ts:135

Returns whether the observed query is currently stale and configured (via the refetchOnReconnect option) to refetch when the network reconnects.

Returns#

boolean

true if the observer should refetch the query on reconnect.

shouldFetchOnWindowFocus()#

shouldFetchOnWindowFocus(): boolean;

Defined in: packages/query-core/src/queryObserver.ts:149

Returns whether the observed query is currently stale and configured (via the refetchOnWindowFocus option) to refetch when the window regains focus.

Returns#

boolean

true if the observer should refetch the query on window focus.

subscribe()#

subscribe(listener: QueryObserverListener): () => void;

Defined in: packages/query-core/src/subscribable.ts:28

Registers a listener to be called on every update this object notifies about. Returns a function that removes the listener again — call it to stop listening. The base class never drops a listener on its own, though some subclasses clear all of theirs in destroy().

Parameters#

listener#

QueryObserverListener

Called on each update, with whatever the subclass passes to its subscribers.

Returns#

A function that removes the listener.

(): void;

Returns#

void

Example#

const unsubscribe = subscribable.subscribe(() => {
  // react to the update
})

unsubscribe()

Inherited from#

Subscribable.subscribe

trackProp()#

trackProp(key: 
  | "error"
  | "data"
  | "isError"
  | "isPending"
  | "isLoading"
  | "isLoadingError"
  | "isRefetchError"
  | "isSuccess"
  | "isPlaceholderData"
  | "status"
  | "dataUpdatedAt"
  | "errorUpdatedAt"
  | "failureCount"
  | "failureReason"
  | "errorUpdateCount"
  | "isFetched"
  | "isFetchedAfterMount"
  | "isFetching"
  | "isInitialLoading"
  | "isPaused"
  | "isRefetching"
  | "isStale"
  | "isEnabled"
  | "refetch"
  | "fetchStatus"): void;

Defined in: packages/query-core/src/queryObserver.ts:358

Records that the given QueryObserverResult property was read, so a subsequent update only notifies this observer if a tracked property actually changed. Normally called indirectly via QueryObserver#trackResult's proxy; exposed directly for adapters that track property access themselves (e.g. through their own reactivity system) instead of via the proxy.

Parameters#

key#

The name of the property that was read.

"error" | "data" | "isError" | "isPending" | "isLoading" | "isLoadingError" | "isRefetchError" | "isSuccess" | "isPlaceholderData" | "status" | "dataUpdatedAt" | "errorUpdatedAt" | "failureCount" | "failureReason" | "errorUpdateCount" | "isFetched" | "isFetchedAfterMount" | "isFetching" | "isInitialLoading" | "isPaused" | "isRefetching" | "isStale" | "isEnabled" | "refetch" | "fetchStatus"

Returns#

void

trackResult()#

trackResult(result: QueryObserverResult<TData, TError>, onPropTracked?: (key: 
  | "error"
  | "data"
  | "isError"
  | "isPending"
  | "isLoading"
  | "isLoadingError"
  | "isRefetchError"
  | "isSuccess"
  | "isPlaceholderData"
  | "status"
  | "dataUpdatedAt"
  | "errorUpdatedAt"
  | "failureCount"
  | "failureReason"
  | "errorUpdateCount"
  | "isFetched"
  | "isFetchedAfterMount"
  | "isFetching"
  | "isInitialLoading"
  | "isPaused"
  | "isRefetching"
  | "isStale"
  | "isEnabled"
  | "refetch"
| "fetchStatus") => void): QueryObserverResult<TData, TError>;

Defined in: packages/query-core/src/queryObserver.ts:338

Wraps a QueryObserverResult in a Proxy that records which properties are read, via QueryObserver#trackProp (and an optional onPropTracked callback). Used by framework adapters when notifyOnChangeProps is not set, to implement its default "only re-render on properties you actually read" behavior.

Parameters#

result#

QueryObserverResult<TData, TError>

The result to wrap.

onPropTracked?#

(key: | "error" | "data" | "isError" | "isPending" | "isLoading" | "isLoadingError" | "isRefetchError" | "isSuccess" | "isPlaceholderData" | "status" | "dataUpdatedAt" | "errorUpdatedAt" | "failureCount" | "failureReason" | "errorUpdateCount" | "isFetched" | "isFetchedAfterMount" | "isFetching" | "isInitialLoading" | "isPaused" | "isRefetching" | "isStale" | "isEnabled" | "refetch" | "fetchStatus") => void

Called with the name of each property that is read.

Returns#

QueryObserverResult<TData, TError>

A proxy of result that tracks property reads.

updateResult()#

updateResult(): void;

Defined in: packages/query-core/src/queryObserver.ts:745

Recomputes and stores the current result from the current query/options, notifying listeners if it changed. Framework adapters call this right after subscribing to make sure no query update was missed in the gap between creating the observer and subscribing to it.

Returns#

void