reverted:
--- b/core/modules/migrate/config/schema/migrate.data_types.schema.yml
+++ a/core/modules/migrate/config/schema/migrate.data_types.schema.yml
@@ -24,9 +24,6 @@
 migrate_source_sql:
   type: migrate_source
   mapping:
-    id_list:
-      type: sequence
-      label: 'Source IDs to be migrated'
     target:
       type: string
       label: 'The migration database target'
diff -u b/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php b/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php
--- b/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php
+++ b/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php
@@ -84,6 +84,14 @@
   protected $originalHighWater;
 
   /**
+   * List of source IDs to process. Each ID in the list is an array of values,
+   * to support multi-value keys.
+   *
+   * @var array[]
+   */
+  protected $idList = [];
+
+  /**
    * Whether this instance should cache the source count.
    *
    * @var bool
@@ -139,9 +147,6 @@
 
   // @TODO, find out how to remove this.
   // @see https://www.drupal.org/node/2443617
-  /**
-   * @var \Drupal\migrate\MigrateExecutableInterface
-   */
   public $migrateExecutable;
 
   /**
@@ -190,27 +195,16 @@
   }
 
   /**
-   * Get the list of IDs of the rows to be migrated.
-   *
-   * @return array
-   *   The list of IDs of the rows to be migrated.
+   * {@inheritdoc}
    */
-  protected function getIdList() {
-    if (!empty($this->configuration['id_list'])) {
-      // @TODO: Add support for multiple IDs https://www.drupal.org/node/2529744
-      if (count($this->getIds()) != 1) {
-        throw new \LogicException('Source IDs can only be specified by a list if there is only one id.');
-      }
-      return $this->configuration['id_list'];
-    }
-    return [];
+  public function setIdList(array $id_list) {
+    $this->idList = $id_list;
   }
 
   /**
    * {@inheritdoc}
    */
   public function prepareRow(Row $row) {
-
     $result = TRUE;
     $result_hook = $this->getModuleHandler()->invokeAll('migrate_prepare_row', array($row, $this, $this->migration));
     $result_named_hook = $this->getModuleHandler()->invokeAll('migrate_' . $this->migration->id() . '_prepare_row', array($row, $this, $this->migration));
@@ -242,7 +236,7 @@
   /**
    * Returns the iterator that will yield the row arrays to be processed.
    *
-   * @return \Iterator|\Countable
+   * @return \Iterator
    */
   public function getIterator() {
     if (!isset($this->iterator)) {
@@ -312,6 +306,7 @@
   public function next() {
     $this->currentSourceIds = NULL;
     $this->currentRow = NULL;
+    $id_list = array_map('reset', $this->idList);
 
     // In order to find the next row we want to process, we ask the source
     // plugin for the next possible row.
@@ -330,11 +325,11 @@
 
       // In case we have specified an ID list, but the ID given by the source is
       // not in there, we skip the row.
-      $id_list = $this->getIdList();
       $id_in_the_list = $id_list && in_array(reset($this->currentSourceIds), $id_list);
       if ($id_list && !$id_in_the_list) {
         continue;
       }
+
       // Preparing the row gives source plugins the chance to skip.
       if ($this->prepareRow($row) === FALSE) {
         continue;
diff -u b/core/modules/migrate/src/Plugin/migrate/source/SqlBase.php b/core/modules/migrate/src/Plugin/migrate/source/SqlBase.php
--- b/core/modules/migrate/src/Plugin/migrate/source/SqlBase.php
+++ b/core/modules/migrate/src/Plugin/migrate/source/SqlBase.php
@@ -117,15 +117,18 @@
     $this->addQueryInfo();
 
     // If an ID list is provided, filter on it.
-    if ($id_list = $this->getIdList()) {
-      foreach ($this->getIds() as $field => $definition) {
-        // If a table alias was provided, prepend it in order to prevent
-        // the possibility of 'ambiguous column' errors.
-        if (isset($definition['alias'])) {
-          $field = $definition['alias'] . '.' . $field;
-        }
-        $this->query->condition($field, $id_list, 'IN');
+    if ($this->idList) {
+      // @TODO: Add support for multiple IDs https://www.drupal.org/node/2529744.
+      $id_info = $this->getIds();
+      $field = key($id_info);
+      $definition = $id_info[$field];
+      // If a table alias was provided, prepend it in order to prevent
+      // the possibility of 'ambiguous column' errors.
+      if (isset($definition['alias'])) {
+        $field = $definition['alias'] . '.' . $field;
       }
+      // For now, just use the first element of each ID array.
+      $this->query->condition($field, array_map('reset', $this->idList), 'IN');
     }
     else {
       /** @var \Drupal\Core\Database\Query\Condition $conditions */
diff -u b/core/modules/migrate/tests/src/Unit/MigrateSourceTest.php b/core/modules/migrate/tests/src/Unit/MigrateSourceTest.php
--- b/core/modules/migrate/tests/src/Unit/MigrateSourceTest.php
+++ b/core/modules/migrate/tests/src/Unit/MigrateSourceTest.php
@@ -172,7 +172,8 @@
    * Test that the when a source id is in the idList, we don't get a row.
    */
   public function testIdInList() {
-    $source = $this->getSource(['id_list' => ['test_sourceid1']]);
+    $source = $this->getSource();
+    $source->setIdList([['test_sourceid1']]);
 
     $source->rewind();
 
only in patch2:
unchanged:
--- a/core/modules/migrate/src/Plugin/MigrateSourceInterface.php
+++ b/core/modules/migrate/src/Plugin/MigrateSourceInterface.php
@@ -62,4 +62,12 @@ public function __toString();
    */
   public function getIds();
 
+  /**
+   * Set the list of source IDs to be processed. Each ID in the list is an
+   * array of key values (supporting multi-field keys).
+   *
+   * @param array[] $id_list
+   */
+  public function setIdList(array $id_list);
+
 }