How to load a apache solr document and send it for reindex after editing is done in drupal 7 As title says,

I want to load a particular node's document and When the editing is done, I need to send the modified document to Solr for re-index programtically.

How it can be done?
When using the apachesolr module, nodes are automatically marked for reindexing after an edit.  So there is nothing you need to do.

If for some reason you need to manually mark a node, the code is

apachesolr_mark_entity('node', $nid);