What are the steps to retrieve data from MySql DB through Hibernate, considering the occurrence of 'Null' values or un-mapped entities during the retrieval process?

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Define the data model: First, define the data model in the source code using annotations or XML files. This includes defining the entities, attributes, and relationships between them.

Create a SessionFactory: Create a SessionFactory object to connect to the database using Hibernate. This involves setting up the database configuration such as database name, username, password, and JDBC driver.

Open a Session: Open a Hibernate session object using the SessionFactory object. This allows the application to interact with the database via Hibernate.

Retrieve data: Once the session is open, use the session object to query the database and retrieve the required data. Use HQL (Hibernate Query Language) or criteria API to specify the query and use the executeQuery method to retrieve the data.

Handle null values: Handle null values in the retrieved data by checking the attribute values for null before using them in the application. Handle missing entities by ensuring that all entities used in queries are correctly mapped in the data model.

Close the session: Close the Hibernate session after completing the data retrieval process. This will release the database connections and free up any system resources used by the session.