fix belongsTo reload for async relationships

addon/-private/system/promise-proxies.js

@@ -82,6 +82,21 @@ export function promiseArray(promise, label) {
   });
 }
 
+export function proxyToContent(method) {
+  return function() {
+    return get(this, 'content')[method](...arguments);
+  };
+}
+
+export const PromiseBelongsTo = PromiseObject.extend({
+  reload() {
+    assert('You are trying to reload an async belongsTo before it has been created', get(this, 'content'));
+    this.get('_belongsToState').reload();
+
+    return this;
+  }
+});
+
 /**
   A PromiseManyArray is a PromiseArray that also proxies certain method calls
   to the underlying manyArray.
@@ -99,13 +114,6 @@ export function promiseArray(promise, label) {
   @namespace DS
   @extends Ember.ArrayProxy
 */
-
-export function proxyToContent(method) {
-  return function() {
-    return get(this, 'content')[method](...arguments);
-  };
-}
-
 export const PromiseManyArray = PromiseArray.extend({
   reload() {
     assert('You are trying to reload an async manyArray before it has been created', get(this, 'content'));

addon/-private/system/relationships/state/belongs-to.js

@@ -2,7 +2,7 @@ import { Promise as EmberPromise } from 'rsvp';
 import { assert, inspect } from '@ember/debug';
 import { assertPolymorphicType } from 'ember-data/-debug';
 import {
-  PromiseObject
+  PromiseBelongsTo
 } from "../../promise-proxies";
 import Relationship from "./relationship";
 
@@ -13,6 +13,7 @@ export default class BelongsToRelationship extends Relationship {
     this.key = relationshipMeta.key;
     this.inverseInternalModel = null;
     this.canonicalState = null;
+    this._loadingPromise = null;
   }
 
   setInternalModel(internalModel) {
@@ -172,10 +173,9 @@ export default class BelongsToRelationship extends Relationship {
         promise = this.findRecord();
       }
 
-      return PromiseObject.create({
-        promise: promise,
-        content: this.inverseInternalModel ? this.inverseInternalModel.getRecord() : null
-      });
+      let record = this.inverseInternalModel ? this.inverseInternalModel.getRecord() : null
+
+      return this._updateLoadingPromise(promise, record);
     } else {
       if (this.inverseInternalModel === null) {
         return null;
@@ -186,19 +186,43 @@ export default class BelongsToRelationship extends Relationship {
     }
   }
 
-  reload() {
-    // TODO handle case when reload() is triggered multiple times
+  _updateLoadingPromise(promise, content) {
+    if (this._loadingPromise) {
+      if (content) {
+        this._loadingPromise.set('content', content)
+      }
+      this._loadingPromise.set('promise', promise)
+    } else {
+      this._loadingPromise = PromiseBelongsTo.create({
+        _belongsToState: this,
+        promise,
+        content
+      });
+    }
 
-    if (this.link) {
-      return this.fetchLink();
+    return this._loadingPromise;
+  }
+
+  reload() {
+    // we've already fired off a request
+    if (this._loadingPromise) {
+      if (this._loadingPromise.get('isPending')) {
+        return this._loadingPromise;
+      }
     }
 
-    // reload record, if it is already loaded
-    if (this.inverseInternalModel && this.inverseInternalModel.hasRecord) {
-      return this.inverseInternalModel.getRecord().reload();
+    let promise;
+
+    if (this.link) {
+      promise = this.fetchLink();
+    } else if (this.inverseInternalModel && this.inverseInternalModel.hasRecord) {
+      // reload record, if it is already loaded
+      promise = this.inverseInternalModel.getRecord().reload();
+    } else {
+      promise = this.findRecord();
     }
 
-    return this.findRecord();
+    return this._updateLoadingPromise(promise);
   }
 
   localStateIsEmpty() {

tests/integration/relationships/belongs-to-test.js

@@ -1380,28 +1380,28 @@ test("A belongsTo relationship can be reloaded using the reference if it was fet
   });
 });
 
-test("A sync belongsTo relationship can be reloaded using a reference if it was fetched via id", function(assert) {
+test("A synchronous belongsTo relationship can be reloaded using a reference if it was fetched via id", function(assert) {
   Chapter.reopen({
-    book: DS.belongsTo()
+    book: DS.belongsTo({ async: false })
   });
 
   let chapter;
   run(() => {
     chapter = env.store.push({
       data: {
         type: 'chapter',
-        id: 1,
+        id: '1',
         relationships: {
           book: {
-            data: { type: 'book', id: 1 }
+            data: { type: 'book', id: '1' }
           }
         }
       }
     });
     env.store.push({
       data: {
         type: 'book',
-        id: 1,
+        id: '1',
         attributes: {
           name: "book title"
         }
@@ -1412,7 +1412,7 @@ test("A sync belongsTo relationship can be reloaded using a reference if it was
   env.adapter.findRecord = function() {
     return resolve({
       data: {
-        id: 1,
+        id: '1',
         type: 'book',
         attributes: { name: 'updated book title' }
       }

tests/integration/relationships/json-api-links-test.js

@@ -774,7 +774,7 @@ function shouldFetchLinkTests(description, payloads) {
 
     assert.ok(!!home, 'We found our home');
 
-    run(() => home.then(h => h.reload()));
+    run(() => home.reload());
   });
   test(`get+unload+get belongsTo with ${description}`, function(assert) {
     assert.expect(3);
@@ -1080,7 +1080,7 @@ function shouldReloadWithLinkTests(description, payloads) {
 
     assert.ok(!!home, 'We found our home');
 
-    run(() => home.then(h => h.reload()));
+    run(() => home.reload());
   });
   test(`get+unload+get belongsTo with ${description}`, function(assert) {
     assert.expect(2);
@@ -1356,7 +1356,7 @@ test(`get+reload belongsTo with data, no links`, function(assert) {
 
   assert.ok(!!home, 'We found our home');
 
-  run(() => home.then(h => h.reload()));
+  run(() => home.reload());
 });
 test(`get+unload+get belongsTo with data, no links`, function(assert) {
   assert.expect(3);
@@ -1616,7 +1616,7 @@ test(`get+reload belongsTo with missing data setup from the other side, no links
 
   assert.ok(!!home, 'We found our home');
 
-  run(() => home.then(h => h.reload()));
+  run(() => home.reload());
 });
 test(`get+unload+get belongsTo with missing data setup from the other side, no links`, function(assert) {
   assert.expect(2);