Find Entity using Drupal EntityQuery

You can find any entity using Drupal 8 EntityQuery System.

Example 1. Taxonomy

Get list of all taxonomy terms

    $query = \Drupal::entityQuery('taxonomy_term');

    $tids = $query->execute();

Get term id of the vocabulary 'tags'

    $query = \Drupal::entityQuery('taxonomy_term');

    $query->condition('vid', 'tags');

    $tids = $query->execute();

Example 2. Node

Find all nodes where the title contains 'drupal'

    $query = \Drupal::entityQuery('node');

    $query->condition('title', '%drupal%','LIKE');

    $nids = $query->execute();

Example 3. User

Fiend all users who's name contains 'admin'

    $query = \Drupal::entityQuery('user');

    $query->condition('name', '%admin%','LIKE');

    $ids = $query->execute();

Example 4. Node with OR condition

    $query = \Drupal::entityQuery('node');

    $group = $query->orConditionGroup()

        ->condition('type', 'page')

        ->condition('type', 'article');

    $entity_ids = $query

        ->condition('title', '%drupal%','LIKE')

        ->condition($group)

        ->execute();

Example 5. With multiple AND + OR conditions

$query->condition('type', $type);

$query_or = $query->orConditionGroup();

$query_and = $query->andConditionGroup()

  ->condition('end1', $end1)

  ->condition('end2', $end2);

$query_or->condition($query_and);

$query_and = $query->andConditionGroup()

  ->condition('end1', $end2)

  ->condition('end2', $end1);

$query_or->condition($query_and);

$query->condition($query_or);

Example 6. Check A field value is NULL or is Not Null

$query = \Drupal::entityQuery('the_entity');

$query->notExists('field_to_check');//Check A field value is NULL

//OR

$query->exists('field_to_check');//Check A field value is NOT NULL

ids = $query->execute();