Function hydrate

packages/query-core/src/hydration.ts:165–269

(
  client: QueryClient,
  dehydratedState: unknown,
  options?: HydrateOptions,
)

}

export function hydrate(
  client: QueryClient,
  dehydratedState: unknown,
  options?: HydrateOptions,
): void {
  if (typeof dehydratedState !== 'object' || dehydratedState === null) {
    return
  }

  const mutationCache = client.getMutationCache()
  const queryCache = client.getQueryCache()
  const deserializeData =
    options?.defaultOptions?.deserializeData ??
    client.getDefaultOptions().hydrate?.deserializeData ??
    defaultTransformerFn

  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
  const mutations = (dehydratedState as DehydratedState).mutations || []
  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
  const queries = (dehydratedState as DehydratedState).queries || []

  mutations.forEach(({ state, ...mutationOptions }) => {
    mutationCache.build(
      client,
      {
        ...client.getDefaultOptions().hydrate?.mutations,
        ...options?.defaultOptions?.mutations,
        ...mutationOptions,
      },
      state,
    )
  })

  queries.forEach(
    ({ queryKey, state, queryHash, meta, promise, dehydratedAt }) => {
      const syncData = promise ? tryResolveSync(promise) : undefined
      const rawData = state.data === undefined ? syncData?.data : state.data
      const data = rawData === undefined ? rawData : deserializeData(rawData)

      let query = queryCache.get(queryHash)
      const existingQueryIsPending = query?.state.status === 'pending'
      const existingQueryIsFetching = query?.state.fetchStatus === 'fetching'

      // Do not hydrate if an existing query exists with newer data
      if (query) {
        const hasNewerSyncData =
          syncData &&
          // We only need this undefined check to handle older dehydration
          // payloads that might not have dehydratedAt
          dehydratedAt !== undefined &&
          dehydratedAt > query.state.dataUpdatedAt
        if (
          state.dataUpdatedAt > query.state.dataUpdatedAt ||
          hasNewerSyncData
        ) {
          // omit fetchStatus from dehydrated state
          // so that query stays in its current fetchStatus
          const { fetchStatus: _ignored, ...serializedState } = state