[BUGFIX identifiers] Address issue with polymorphic findRecord

packages/-ember-data/tests/integration/identifiers/polymorphic-scenarios-test.ts

@@ -61,7 +61,34 @@ module('Integration | Identifiers - single-table-inheritance polymorphic scenari
       store = owner.lookup('service:store');
     });
 
-    test(`Identity of polymorphic relations can change type`, async function(assert) {
+    test(`Identity of polymorphic relations can change type on first load`, async function(assert) {
+      const { owner } = this;
+      class TestAdapter extends Adapter {
+        shouldBackgroundReloadRecord() {
+          return false;
+        }
+        findRecord(_, __, id) {
+          return resolve({
+            data: {
+              id,
+              type: 'ferrari',
+              attributes: {
+                color: 'red',
+              },
+            },
+          });
+        }
+      }
+      owner.register('adapter:application', TestAdapter);
+
+      const foundFerrari = await store.findRecord('car', '1');
+      assert.strictEqual(foundFerrari.constructor.modelName, 'ferrari', 'We found the right type');
+
+      const cachedFerrari = await store.peekRecord('ferrari', '1');
+      assert.strictEqual(cachedFerrari.constructor.modelName, 'ferrari', 'We cached the right type');
+    });
+
+    test(`Identity of polymorphic relations can change type when in cache`, async function(assert) {
       const { owner } = this;
       const requests: RID[] = [];
       const expectedRequests = [

packages/store/addon/-private/identifiers/cache.ts

@@ -1,4 +1,5 @@
 import { warn } from '@ember/debug';
+import { assign } from '@ember/polyfills';
 import { DEBUG } from '@glimmer/env';
 
 import coerceId from '../system/coerce-id';
@@ -343,6 +344,17 @@ export class IdentifierCache {
     let newId = coerceId(data.id);
     let existingIdentifier = detectMerge(this._cache.types, identifier, data, newId, this._cache.lids);
 
+    if (!existingIdentifier) {
+      // If the incoming type does not match the identifier type, we need to create an identifier for the incoming
+      // data so we can merge the incoming data with the existing identifier, see #7325 and #7363
+      if (data.type && identifier.type !== normalizeModelName(data.type)) {
+        let incomingDataResource = assign({}, data);
+        // Need to strip the lid from the incomingData in order force a new identifier creation
+        delete incomingDataResource.lid;
+        existingIdentifier = this.getOrCreateRecordIdentifier(incomingDataResource);
+      }
+    }
+
     if (existingIdentifier) {
       let keyOptions = getTypeIndex(this._cache.types, identifier.type);
       identifier = this._mergeRecordIdentifiers(keyOptions, identifier, existingIdentifier, data, newId as string);