Provide a views relationship for each dynamic entity reference field

With test fix.

Well this passes locally.

Keeping up with the core.

Just debugging.

It is broken again :/

Minor fixes

This is blocked on #2366093: Unable to set field value programmatically.

Reroll after #2366093: Unable to set field value programmatically.. This is blocked on #2372745: KernelTestBase ignores extensions in site-specific directories now.

Also blocked on #2378729: JoinPluginBase doesn't allow extra conditions on left table

Reroll and fixes. Core patch is dependent on join issue.

All the blockers are fixed now. Let's fix this issue as well.

Test fix.

Added some docs as per @dawehner suggestions.

Fixes after #2451679: Validate cache contexts (+ cache contexts in some views plugins wrong). I'll commit it once the HEAD is back green.
@socketwench everything is working fine for me.

I think we have a similar problem here #2451789: Entity reference joins to the wrong base table in views..

Fixes after #2451789: Entity reference joins to the wrong base table in views.. Need to rewrite DynamicEntityReferenceRelationshipTest just like EntityReferenceRelationshipTest

Copy paste fix.

Ok we have an issue now. I have been adding and extra condition to join which checks target type of current relationship. It works fine for single relationship but for multiple relationships join produce no result because a single value can't have two values of target types as can be seen in the resultant query.

SELECT entity_test.id AS id, entity_test_entity_test__field_test.id AS entity_test_entity_test__field_test_id, entity_test_mul_property_data_entity_test__field_test.id AS entity_test_mul_property_data_entity_test__field_test_id
FROM 
`entity_test` entity_test
LEFT JOIN `entity_test__field_test` entity_test__field_test ON entity_test.id = entity_test__field_test.entity_id AND entity_test__field_test.deleted = '0'
INNER JOIN `entity_test` entity_test_entity_test__field_test ON entity_test__field_test.field_test_target_id = entity_test_entity_test__field_test.id AND entity_test__field_test.field_test_target_type = 'entity_test'
INNER JOIN `entity_test_mul_property_data` entity_test_mul_property_data_entity_test__field_test ON entity_test__field_test.field_test_target_id = entity_test_mul_property_data_entity_test__field_test.id AND entity_test__field_test.field_test_target_type = 'entity_test_mul'
LIMIT 10 OFFSET 0

The why around this would be if we'd add WHERE clause in the query instead of extra join condition something like this.

SELECT entity_test.id AS id, entity_test_entity_test__field_test.id AS entity_test_entity_test__field_test_id, entity_test_mul_property_data_entity_test__field_test.id AS entity_test_mul_property_data_entity_test__field_test_id
FROM 
`entity_test` entity_test
LEFT JOIN `entity_test__field_test` entity_test__field_test ON entity_test.id = entity_test__field_test.entity_id AND entity_test__field_test.deleted = '0'
INNER JOIN `entity_test` entity_test_entity_test__field_test ON entity_test__field_test.field_test_target_id = entity_test_entity_test__field_test.id
INNER JOIN `entity_test_mul_property_data` entity_test_mul_property_data_entity_test__field_test ON entity_test__field_test.field_test_target_id = entity_test_mul_property_data_entity_test__field_test.id
WHERE entity_test__field_test.field_test_target_type IN ('entity_test', 'entity_test_mul')
LIMIT 10 OFFSET 0

The problem with this approach is it produced duplicate results just like when we add a relationship with term and term parent in node view. This can be avoided using distinct. Producing duplicates is fine IMO to avoid it user can always turn distinct on. If we'd go by this solution we'd have to implement a views relationship plugin which will add this where clause.

Do we've any other way around that?

Meanwhile I updated the tests. Currently it only asserts views data. Just have to create some views like EntityReferenceRelationshipTest and check the relationships but we have to finalize the approach first.

Oh I just made relationships required. You are right that's the reason I'm not getting results.
Though making those relationships not required gives me this error. Let me debug some more. Thanks for the replay.

Uncaught AjaxError: 
An AJAX HTTP error occurred.
HTTP Result Code: 200
Debugging information follows.
Path: /admin/structure/views/view/test_dynamic_entity_reference_entity_test_view/preview/default
StatusText: OK
ResponseText: 
( ! ) Fatal error: Call to a member function bundle() on a non-object in /vagrant/app/core/modules/views/src/Entity/Render/EntityFieldRenderer.php on line 203
Call Stack
#TimeMemoryFunctionLocation
10.0001265320{main}(  )../index.php:0
20.0008569968Drupal\Core\DrupalKernel->handle(  )../index.php:19
30.00521320048Stack\StackedHttpKernel->handle(  )../DrupalKernel.php:572
40.00521320176Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(  )../StackedHttpKernel.php:23
50.00521320992Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(  )../NegotiationMiddleware.php:67
60.00541321104Drupal\page_cache\StackMiddleware\PageCache->handle(  )../ReverseProxyMiddleware.php:58
70.00541321704Drupal\page_cache\StackMiddleware\PageCache->pass(  )../PageCache.php:83
80.00541321752Drupal\Core\DependencyInjection\Container\prod\Drupal_Core_StackMiddleware_KernelPreHandle_Proxy->handle(  )../PageCache.php:104
90.00551325328Drupal\Core\StackMiddleware\KernelPreHandle->handle(  )../73041b7dda6cde1a1c2665c605705b0de53416cf44a31cd564c06e134fe42808.php:9254
100.00881900464Drupal\Core\DependencyInjection\Container\prod\Drupal_Core_StackMiddleware_Session_Proxy->handle(  )../KernelPreHandle.php:53
110.00891905176Drupal\Core\StackMiddleware\Session->handle(  )../73041b7dda6cde1a1c2665c605705b0de53416cf44a31cd564c06e134fe42808.php:9304
120.02202061552Drupal\Core\DependencyInjection\Container\prod\Symfony_Component_HttpKernel_HttpKernel_Proxy->handle(  )../Session.php:62
130.02232086080Symfony\Component\HttpKernel\HttpKernel->handle(  )../73041b7dda6cde1a1c2665c605705b0de53416cf44a31cd564c06e134fe42808.php:9194
140.02242087032Symfony\Component\HttpKernel\HttpKernel->handleRaw(  )../HttpKernel.php:68
150.16498506920call_user_func_array:{/vagrant/app/core/vendor/symfony/http-kernel/HttpKernel.php:147}
(  )../HttpKernel.php:147
160.16498507616Drupal\Core\Controller\FormController->getContentResult(  )../HttpKernel.php:147
170.16538711776Drupal\Core\Form\FormBuilder->buildForm(  )../FormController.php:79
180.610918415512Drupal\Core\Form\FormBuilder->processForm(  )../FormBuilder.php:265
190.612018457680Drupal\Core\Form\FormBuilder->rebuildForm(  )../FormBuilder.php:554
200.612018457680Drupal\Core\Form\FormBuilder->retrieveForm(  )../FormBuilder.php:306
210.612018460304call_user_func_array:{/vagrant/app/core/lib/Drupal/Core/Form/FormBuilder.php:442}
(  )../FormBuilder.php:442
220.612018460872Drupal\views_ui\ViewFormBase->buildForm(  )../FormBuilder.php:442
230.612018460872Drupal\Core\Entity\EntityForm->buildForm(  )../ViewFormBase.php:46
240.612118460920Drupal\views_ui\ViewPreviewForm->form(  )../EntityForm.php:105
250.612218468784Drupal\views_ui\ViewUI->renderPreview(  )../ViewPreviewForm.php:65
260.613718501104Drupal\views\ViewExecutable->preview(  )../ViewUI.php:634
270.623218755256Drupal\views\Plugin\views\display\DisplayPluginBase->preview(  )../ViewExecutable.php:1548
280.623218756128Drupal\views\ViewExecutable->render(  )../DisplayPluginBase.php:2386
290.650119004448Drupal\views\Plugin\views\display\DisplayPluginBase->render(  )../ViewExecutable.php:1431
300.650119004632Drupal\views\Plugin\views\style\StylePluginBase->render(  )../DisplayPluginBase.php:2126
310.650119004984Drupal\views\Plugin\views\style\StylePluginBase->renderGrouping(  )../StylePluginBase.php:455
320.650119005536Drupal\views\Plugin\views\style\StylePluginBase->renderFields(  )../StylePluginBase.php:557
330.650319018584Drupal\Core\Render\Renderer->render(  )../StylePluginBase.php:681
340.650319019872Drupal\Core\Render\Renderer->doRender(  )../Renderer.php:158
350.650419034504call_user_func:{/vagrant/app/core/lib/Drupal/Core/Render/Renderer.php:320}
(  )../Renderer.php:320
360.650419034600Drupal\views\Plugin\views\style\StylePluginBase->elementPreRenderRow(  )../Renderer.php:320
370.751919956024Drupal\views\Plugin\views\field\FieldPluginBase->theme(  )../StylePluginBase.php:728
380.751919958416Drupal\Core\Render\Renderer->render(  )../FieldPluginBase.php:1657
390.751919958464Drupal\Core\Render\Renderer->doRender(  )../Renderer.php:158
400.751919961776Drupal\Core\Theme\ThemeManager->render(  )../Renderer.php:380
410.751919961776Drupal\Core\Theme\ThemeManager->theme(  )../ThemeManager.php:98
420.752019964120template_preprocess_views_view_field(  )../ThemeManager.php:300
430.752019964120Drupal\views\Plugin\views\field\FieldPluginBase->advancedRender(  )../views.theme.inc:277
440.752019964120Drupal\views\Plugin\views\field\Field->getItems(  )../FieldPluginBase.php:1125
450.752019964120Drupal\views\Entity\Render\EntityFieldRenderer->render(  )../Field.php:808
460.752019964120Drupal\views\Entity\Render\EntityFieldRenderer->buildFields(  )../EntityFieldRenderer.php:130

I didn't debug the above error but thanks to @olli it is blocked on #2534780: Fatal error rendering fields using an optional relationship.

This is finally complete now with tests for all the cases.

1. A DER field can create relationships with multiple entity types.
2. A DER field can create mutliple reverse relationships with multiple entity types.

In tests I only added one test per display to keep things simple.

Thanks for the review @dawehner

1. We should add dedicate tests with entity_test_der in which der is a basefield and whatever problem we'll find there we'll fix it follow up. I think for basic views implementation we should not block this issue on this point.
2. Anything to fix here?
3. getDedicatedDataTableName is not defined on the interface $table_mapping->getDedicatedDataTableName($field_storage),
4. I really like the idea. I'll create a follow up for this.

Created follow up issues.

1. Added #2542274: Write tests for DER field as basefield on an entity
2. No op
3. Added #2542282: Add all the DefaultTableMapping public methods to TableMappingInterface
4. Added #2542280: Get base table properly for views relationships. @dawehner please leave a comment for proposed resolution.

Committed and pushed to 8.x-1.x.

Thanks @dawehner for the reviews.
Thanks @damiankloip for discussing the issue with me at DrupalCon Amsterdam.
Thanks @larowlan for the manual testing.