fix(select): clear select if no option matches value

Closes #2109

Author: kara

src/lib/select/select.spec.ts

@@ -191,19 +191,19 @@ describe('MdSelect', () => {
     });
 
     it('should focus the selected option if an option is selected', async(() => {
-      trigger.click();
-      fixture.detectChanges();
-
-      const options =
-        overlayContainerElement.querySelectorAll('md-option') as NodeListOf<HTMLElement>;
-      options[1].click();
-      fixture.detectChanges();
+      // must wait for initial writeValue promise to finish
+      fixture.whenStable().then(() => {
+        fixture.componentInstance.control.setValue('pizza-1');
+        fixture.detectChanges();
 
-      trigger.click();
-      fixture.detectChanges();
+        trigger.click();
+        fixture.detectChanges();
 
-      fixture.whenStable().then(() => {
-        expect(fixture.componentInstance.select._keyManager.focusedItemIndex).toEqual(1);
+        // must wait for animation to finish
+        fixture.whenStable().then(() => {
+          fixture.detectChanges();
+          expect(fixture.componentInstance.select._keyManager.focusedItemIndex).toEqual(1);
+        });
       });
     }));
 
@@ -305,6 +305,27 @@ describe('MdSelect', () => {
         .toEqual('steak-0', `Expected control's value to be set to the new option.`);
     });
 
+    it('should clear the selection when a nonexistent option value is selected', () => {
+      fixture.componentInstance.control.setValue('pizza-1');
+      fixture.detectChanges();
+
+      fixture.componentInstance.control.setValue('gibberish');
+      fixture.detectChanges();
+
+      const value = fixture.debugElement.query(By.css('.md-select-value'));
+      expect(value).toBe(null, `Expected trigger to be cleared when option value is not found.`);
+      expect(trigger.textContent)
+          .not.toContain('Pizza', `Expected trigger to be cleared when option value is not found.`);
+
+      trigger.click();
+      fixture.detectChanges();
+
+      const options =
+          overlayContainerElement.querySelectorAll('md-option') as NodeListOf<HTMLElement>;
+      expect(options[1].classList)
+          .not.toContain('md-selected', `Expected option with the old value not to be selected.`);
+    });
+
     it('should set the control to touched when the select is touched', () => {
       expect(fixture.componentInstance.control.touched)
         .toEqual(false, `Expected the control to start off as untouched.`);

src/lib/select/select.ts

@@ -252,11 +252,7 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
       return;
     }
 
-    this.options.forEach((option: MdOption) => {
-      if (option.value === value) {
-        option.select();
-      }
-    });
+    this._setSelectionByValue(value);
   }
 
   /**
@@ -353,6 +349,28 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
     scrollContainer.scrollTop = this._scrollTop;
   }
 
+  /**
+   * Sets the selected option based on a value. If no option can be
+   * found with the designated value, the select trigger is cleared.
+   */
+  private _setSelectionByValue(value: any): void {
+    this.options.forEach((option: MdOption) => {
+      if (option.value === value) {
+        option.select();
+      }
+    });
+
+    if (this.selected && this.selected.value !== value) {
+      this._clearSelection();
+    }
+  }
+
+  /** Clears the select trigger and deselects every option in the list. */
+  private _clearSelection(): void {
+    this._selected = null;
+    this._updateOptions();
+  }
+
   private _getTriggerRect(): ClientRect {
     return this.trigger.nativeElement.getBoundingClientRect();
   }