Working with the Entity Manager 
The entity manager allows you to synchronize the persistent state of the entities to the database. It manages entity objects in the following way:
When you need to retrieve information from the database, it returns the respective entities.
When you need to update data in the database, you pass the updated entity objects to the entity manager, so it performs the necessary SQL queries for updating the information. In the business layer, you can also perform explicit queries using an SQL-like query language.
Procedure
You can perform the following subtasks:
Get an entity manager.
More information: Obtaining an Entity Manager Instance
Manage entities, using the entity manager.
More information: Managing Entity Instances
Optionally, create and execute queries, using the query language.
More information: Creating and Executing Queries