Issue #2120839 by damiankloip, slashrm, Dave Reid: File usage view causes fatal error for a file with 0 usage.

core/modules/file/config/views.view.files.yml

@@ -396,7 +396,7 @@ display:
           id: count
           table: file_usage
           field: count
-          relationship: none
+          relationship: fid
           group_type: sum
           admin_label: ''
           label: 'Used in'
@@ -578,7 +578,15 @@ display:
           empty: true
           content: 'No files available.'
           plugin_id: text_custom
-      relationships: {  }
+      relationships:
+        fid:
+          id: fid
+          table: file_managed
+          field: fid
+          relationship: none
+          group_type: group
+          admin_label: 'File usage'
+          required: true
       arguments: {  }
       group_by: '1'
       show_admin_links: '1'
@@ -600,6 +608,16 @@ display:
       defaults:
         pager: true
         pager_options: true
+        relationships: false
+      relationships:
+        fid:
+          id: fid
+          table: file_managed
+          field: fid
+          relationship: none
+          group_type: group
+          admin_label: 'File usage'
+          required: false
   page_2:
     display_plugin: page
     id: page_2
@@ -621,6 +639,7 @@ display:
         arguments: false
         style: false
         row: false
+        relationships: false
       pager:
         type: mini
         options:
@@ -947,6 +966,15 @@ display:
       row:
         type: fields
         options: {  }
+      relationships:
+        fid:
+          id: fid
+          table: file_managed
+          field: fid
+          relationship: none
+          group_type: group
+          admin_label: 'File usage'
+          required: true
 label: Files
 module: file
 id: files

core/modules/file/file.views.inc

@@ -48,6 +48,15 @@ function file_views_data() {
     'sort' => array(
       'id' => 'standard',
     ),
+    'relationship' => array(
+      'title' => t('File usage'),
+      'help' => t('Relate file entities to their usage.'),
+      'id' => 'standard',
+      'base' => 'file_usage',
+      'base field' => 'fid',
+      'field' => 'fid',
+      'label' => t('File usage'),
+    ),
   );
 
   // filename
@@ -180,11 +189,6 @@ function file_views_data() {
   // that we can create relationships from files to entities, and then on each core entity type base
   // table so that we can provide general relationships between entities and files.
   $data['file_usage']['table']['join'] = array(
-    // Link ourself to the {file_managed} table so we can provide file->entity relationships.
-    'file_managed' => array(
-      'field' => 'fid',
-      'left_field' => 'fid',
-    ),
     // Link ourself to the {node} table so we can provide node->file relationships.
     'node' => array(
       'field' => 'id',

core/modules/file/lib/Drupal/file/Tests/FileListingTest.php

@@ -72,6 +72,19 @@ class FileListingTest extends FileFieldTestBase {
       $nodes[] = $this->drupalCreateNode(array('type' => 'article'));
     }
 
+    $this->drupalGet('admin/content/files');
+    $this->assertResponse(200);
+    $this->assertText('No files available.');
+    $this->drupalGet('admin/content/files');
+    $this->assertResponse(200);
+
+    // Create a file with no usage.
+    $file = $this->createFile();
+
+    $this->drupalGet('admin/content/files/usage/' . $file->id());
+    $this->assertResponse(200);
+    $this->assertTitle(t('File usage information for @file | Drupal', array('@file' => $file->getFilename())));
+
     foreach ($nodes as &$node) {
       $this->drupalGet('node/' . $node->id() . '/edit');
       $file = $this->getTestFile('image');
@@ -84,7 +97,6 @@ class FileListingTest extends FileFieldTestBase {
     }
 
     $this->drupalGet('admin/content/files');
-    $this->assertResponse(200);
 
     foreach ($nodes as $node) {
       $file = entity_load('file', $node->file->target_id);
@@ -131,4 +143,29 @@ class FileListingTest extends FileFieldTestBase {
       $this->assertLinkByHref('node/' . $node->id(), 0, 'Link to registering entity found on usage page.');
     }
   }
+
+  /**
+   * Creates and saves a test file.
+   *
+   * @return \Drupal\Core\Entity\EntityInterface
+   *  A file entity.
+   */
+  protected function createFile() {
+    // Create a new file entity.
+    $file = entity_create('file', array(
+      'uid' => 1,
+      'filename' => 'druplicon.txt',
+      'uri' => 'public://druplicon.txt',
+      'filemime' => 'text/plain',
+      'timestamp' => 1,
+      'status' => FILE_STATUS_PERMANENT,
+    ));
+    file_put_contents($file->getFileUri(), 'hello world');
+
+    // Save it, inserting a new record.
+    $file->save();
+
+    return $file;
+  }
+
 }

core/modules/views/lib/Drupal/views/Plugin/views/field/EntityLabel.php

@@ -100,12 +100,15 @@ class EntityLabel extends FieldPluginBase {
    * {@inheritdoc}
    */
   public function render(ResultRow $values) {
-    $entity = $this->loadedReferencers[$this->getValue($values, $this->definition['entity type field'])][$this->getValue($values)];
+    $type = $this->getValue($values, $this->definition['entity type field']);
+    $value = $this->getValue($values);
 
-    if (empty($entity)) {
-      return NULL;
+    if (empty($this->loadedReferencers[$type][$value])) {
+      return;
     }
 
+    $entity = $this->loadedReferencers[$type][$value];
+
     if (!empty($this->options['link_to_entity'])) {
       $uri = $entity->uri();
       $this->options['alter']['make_link'] = TRUE;
@@ -123,7 +126,9 @@ class EntityLabel extends FieldPluginBase {
 
     $entity_ids_per_type = array();
     foreach ($values as $value) {
-      $entity_ids_per_type[$this->getValue($value, 'type')][] = $this->getValue($value);
+      if ($type = $this->getValue($value, 'type')) {
+        $entity_ids_per_type[$type][] = $this->getValue($value);
+      }
     }
 
     foreach ($entity_ids_per_type as $type => $ids) {