Apollo Client TTL example

ttl-example.js

// credit: Ben Newman

// a possible workaround is to store the timestamp info in the field using field policy merge and read functions:

new InMemoryCache({
  typePolicies: {
    SomeType: {
      fields: {
        theField: {
          read(existing) {
            if (existing && existing.storageTime) {
              const elapsedMillis = Date.now() - existing.storageTime;
              if (elapsedMillis > YOUR_DESIRED_TTL) {
                // Returning undefined indicates field is missing
                // Here might be a good place to schedule eviction (not automatic)
                return;
              }
            }
            // If there's nothing in the cache for this field yet, existing will be undefined,
            // so the read function will (correctly) return undefined here:
            return existing && existing.value;
          },

          merge(existing, incoming, { mergeObjects }) {
            // Instead of storing incoming as-is, we store a { value, storageTime } object
            return {
               value: existing ? mergeObjects(existing, incoming) : incoming,
               storageTime: Date.now(),
            };
          },
       },
    },
  },
})
  
// ideally you could use a helper function to simplify applying this logic to multiple fields:
  
new InMemoryCache({
  typePolicies: {
    SomeType: {
      fields: {
        theField: makeTTLFieldPolicy(YOUR_DESIRED_TTL),
        anotherField: makeTTLFieldPolicy(2 * YOUR_DESIRED_TTL),
        // ... and so on ...
       },
    },
  },
})

// where makeTTLFieldPolicy is something like

function makeTTLFieldPolicy(maxElapsedMillis) {
  return {
    read(existing) {
      if (existing && existing.storageTime) {
        const elapsedMillis = Date.now() - existing.storageTime;
        if (elapsedMillis > maxElapsedMillis) {
          return;
        }
      }
      return existing && existing.value;
    },
    merge(existing, incoming, { mergeObjects }) {
      return {
          value: existing ? mergeObjects(existing, incoming) : incoming,
          storageTime: Date.now(),
      };
    },
  };
}