message: Add fallback and error logging guidance to improve PR 823
  When the `relatedIdentity` index is missing on the inverse relationships object store, prevent a hard fail and instead add guidance with a `console.error` message.
diff: @@ -421,7 +421,20 @@ export class IndexedDBCache extends AsyncRecordCache {
  const keyRange = Orbit.globals.IDBKeyRange.only(
  serializeRecordIdentity(recordIdentity)
  );
  - const request = objectStore.index('relatedIdentity').openCursor(keyRange);
  +
  + let index;
  + try {
  + index = objectStore.index('relatedIdentity');
  + } catch (e) {
  + console.error(
  + `[@orbit/indexeddb] The 'relatedIdentity' index is missing from the ${INVERSE_RELS} object store in IndexedDB. ` +
  + 'Please add this index using a DB migration as described in https://github.com/orbitjs/orbit/pull/823'
  + );
  + resolve([]);
  + return;
  + }
  +
  + const request = index.openCursor(keyRange);
  request.onsuccess = (event: any) => {
  const cursor = event.target.result;
  