Fetch Policies

The first step to reusing locally cached data is to pass a fetchPolicy to the loadQuery function, which can be provided by useQueryLoader (see the Fetching Queries section):

const React = require('React');
const {graphql} = require('react-relay');

function AppTabs() {
  const [
    queryRef,
    loadQuery,
  ] = useQueryLoader(HomeTabQuery);

  const onSelectHomeTab = () => {
    loadQuery({id: '4'}, {fetchPolicy: 'store-or-network'});
  }

  // ...
}

The provided fetchPolicy will determine:

• whether the query should be fulfilled from the local cache, and
• whether a network request should be made to fetch the query from the server, depending on the availability of the data for that query in the store.

By default, Relay will try to read the query from the local cache; if any piece of data for that query is missing or stale, it will fetch the entire query from the network. This default fetchPolicy is called "store-or-network".

Specifically, fetchPolicy can be any of the following options: **

• "store-or-network": (default) will reuse locally cached data, and will only send a network request if any data for the query is missing or stale. If the query is fully cached, a network request will not be made.
• "store-and-network": will reuse locally cached data and will always send a network request, regardless of whether any data was missing or stale in the store.
• "network-only": will not reuse locally cached data, and will always send a network request to fetch the query, ignoring any data that might be locally cached and whether it's missing or stale.
• "store-only": will only reuse locally cached data, and will never send a network request to fetch the query. In this case, the responsibility of fetching the query falls to the caller, but this policy could also be used to read and operate on data that is entirely local.

Note that the refetch function discussed in the Fetching and Rendering Different Data section also takes a fetchPolicy.

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