Load the whole database with Hibernate

Question

I am using SQLite3 and Hibernate with Java. Can I somehow load the whole database in memory or fetch all data from the database so that I can access mapped objects fastest? For example if we have a Company and Employee classes and in Company we've mapped the Employees as company.getEmployees(). I would like to fetch all companies from the database and later when I call this method I'd like to get the employees immediately. So is there a way to preload them? Further, if employee is mapped to other objects, can I preload them too? To summarize, I'd like to load the whole database and use the ORM to access the data. Thanks!

Answer 1

If your goal is simply blazing performance you have several options:

• Configure Hibernate 2nd-level cache
• In addition to prior point, configure query cache if your data doens't change much.
• Instead of SQLite use HSQLDB or H2 in-memory SQL databases in embedded mode
• Use ObjectDB with a large shared cache. JPA compliant OODB.
• Use MongoDB. A very fast in-memory NoSQL solution

I suggest ObjectDB if you aren't required to use SQL.

(EDITS: Removed eager fetching, added query cache.)

Answer 2

Set all relationships in your entity classes to eager. If you are using JPA annotations:

public class Company{

private List<Employee> employeeList;

@ManyToMany(fetch = FetchType.EAGER)
public List<Employee> getEmployeeList() {
        return employeeList;
    }
}

This will fetch all the employees automatically when you retrieve a company from database. Please note this could affect the performance dramatically.