Nodes

Nodes are the main content type in Drupal. It's the most common entity that we use in Drupal.

Get Current Node information

$node = \Drupal::routeMatch()->getParameter('node'); // get node

$node_type = $node->getType(); // Node type
$node_bundle = $node->bundle(); // Node type

$nid = $node->id(); // Node id

$title = $node->getTitle(); // Node title

Get current Node information on preview page

  $routeMatch   = \Drupal::routeMatch();
  $node_preview = $routeMatch->getParameter( 'node_preview' );

Get info of a specific Node - NODE::load()

$NODE_TITLE =  Node::load(ID)->getTitle(); // Node title

Query Nodes

There are two methods that I use to query nodes, the first one is the EntityQuery and the second one is the EntityTypeManager. These two are almost exactly the same, if you were to look at the code, you would see that they are using the same methods. The only difference is that the EntityTypeManager is a bit more flexible and it's easier to use.

Get info of a specific Nodes - EntityQuery

$node_ids = Drupal::entityQuery('node')
      ->condition('type', CONTENT_TYPE)
      ->condition('FIELD_NAME', FIELD_ID)
      ->execute(); // Get all the node ids that match these conditions
$nodes = Node::loadMultiple($node_ids); // All the nodes in an assoc array

Get info of a specific Nodes - EntityTypeManager

$node = \Drupal::entityTypeManager()->getStorage('node')
        ->getQuery()
        ->condition('nid', $nid, '=')
        ->condition('type', 'blog')
        ->condition('status', 1)
        ->sort('nid', 'ASC')
        ->range(0, 1)
        ->execute();

$node = array_values($node);
$node = $node[0];

// Or we could use $node = reset($node)

$titulo =  Node::load($node)->getTitle(); // Title

$link = \Drupal::service('path_alias.manager')
          ->getAliasByPath('/node/' . $node);  // Relative url

Reference

For more information about the Node class, check the Node Methods