diff --git a/core/lib/Drupal/Core/Entity/ContentEntityDatabaseStorage.php b/core/lib/Drupal/Core/Entity/ContentEntityDatabaseStorage.php
index f276e8d..f0ff2ae 100644
--- a/core/lib/Drupal/Core/Entity/ContentEntityDatabaseStorage.php
+++ b/core/lib/Drupal/Core/Entity/ContentEntityDatabaseStorage.php
@@ -269,7 +269,7 @@ public function setEntityType(ContentEntityTypeInterface $entity_type) {
   /**
    * {@inheritdoc}
    */
-  public function getTableMapping($storage_definitions = NULL) {
+  public function getTableMapping(array $storage_definitions = NULL) {
     $table_mapping = $this->tableMapping;
 
     if (!isset($this->tableMapping) || $storage_definitions) {
@@ -1442,6 +1442,9 @@ public function onEntityTypeDefinitionUpdate(EntityTypeInterface $original) {
   public function onFieldStorageDefinitionCreate(FieldStorageDefinitionInterface $storage_definition) {
     // If we are adding a field stored in a shared table we need to recompute
     // the table mapping.
+    // @todo This does not belong here. Remove it once we are able to generate a
+    //   fresh table mapping in the schema handler. See
+    //   https://www.drupal.org/node/2274017.
     if ($this->getTableMapping()->allowsSharedTableStorage($storage_definition)) {
       $this->tableMapping = NULL;
     }
diff --git a/core/lib/Drupal/Core/Entity/Sql/DefaultTableMapping.php b/core/lib/Drupal/Core/Entity/Sql/DefaultTableMapping.php
index 22581d8..f950887 100644
--- a/core/lib/Drupal/Core/Entity/Sql/DefaultTableMapping.php
+++ b/core/lib/Drupal/Core/Entity/Sql/DefaultTableMapping.php
@@ -113,6 +113,8 @@ public function getAllColumns($table_name) {
       // There is just one field for each dedicated storage table, thus
       // $field_name can only refer to it.
       if (isset($field_name) && $this->requiresDedicatedTableStorage($this->fieldStorageDefinitions[$field_name])) {
+        // Unlike in shared storage tables, in dedicated ones field columns are
+        // positioned last.
         $this->allColumns[$table_name] = array_merge($this->getExtraColumns($table_name), $this->allColumns[$table_name]);
       }
       else {
diff --git a/core/lib/Drupal/Core/Entity/Sql/SqlEntityStorageInterface.php b/core/lib/Drupal/Core/Entity/Sql/SqlEntityStorageInterface.php
index 1a4e0bc..02174bf 100644
--- a/core/lib/Drupal/Core/Entity/Sql/SqlEntityStorageInterface.php
+++ b/core/lib/Drupal/Core/Entity/Sql/SqlEntityStorageInterface.php
@@ -17,9 +17,13 @@
   /**
    * Gets a table mapping for the entity's SQL tables.
    *
+   * @param \Drupal\Core\Field\FieldStorageDefinitionInterface[] $storage_definitions
+   *   (optional) An array of field storage definitions to be used to compute
+   *   the table mapping. Defaults to the ones provided by the entity manager.
+   *
    * @return \Drupal\Core\Entity\Sql\TableMappingInterface
    *   A table mapping object for the entity's tables.
    */
-  public function getTableMapping();
+  public function getTableMapping(array $storage_definitions = NULL);
 
 }
diff --git a/core/tests/Drupal/Tests/Core/Entity/Schema/ContentEntitySchemaHandlerTest.php b/core/tests/Drupal/Tests/Core/Entity/Schema/ContentEntitySchemaHandlerTest.php
index 932c5b8..1a4bb1f 100644
--- a/core/tests/Drupal/Tests/Core/Entity/Schema/ContentEntitySchemaHandlerTest.php
+++ b/core/tests/Drupal/Tests/Core/Entity/Schema/ContentEntitySchemaHandlerTest.php
@@ -776,7 +776,7 @@ public function testDedicatedTableSchema() {
     ));
 
     // Setup a field having a dedicated schema.
-    $field_name = $this->randomName();
+    $field_name = $this->getRandomGenerator()->name();
     $this->setUpStorageDefinition($field_name, array(
       'columns' => array(
         'shape' => array(