Spring Data Access Object (DAO)

I would like to present a small example of using Data Access Object (DAO) in Spring. This is a kind of component which provides unified interface to communication between application and source of data for instance database or file. Application using DAO does not have to know the way the data is stored or manipulated in database. This component is commonly used in MVC (Model-View-Controller) which allows to separate data access model from business logic and presentation layer. In this example datasource is NoSQL Database MongoDB.

Below I put some example of DAO Entity called SettingsDao and its Implementation called SettingsDaoImpl.

Entity SettingsDAO :

package pl.eventoo.mongodb.dao;

import pl.eventoo.domain.Settings;

/**
 * Interface of credentials settings
 *
 * @author lukasz
 */
public interface SettingsDao {

    /**
     * Interface for save credentials
     *
     * @param settings 
     */
    public void saveSettings(Settings settings);
    
    /**
     * Interface for update credentials
     * 
     * @param settings
     * @return
     */
    public boolean updateSettings(Settings settings);

    /**
     * Interface for read credentials
     *
     * @return
     */
    public Settings readSettings();
}

Implementation of Entity DAO SettingsDaoImpl :

package pl.eventoo.mongodb.dao;

import com.google.code.morphia.DAO;
import com.google.code.morphia.query.UpdateOperations;
import com.google.code.morphia.query.UpdateResults;
import pl.eventoo.domain.Settings;
import pl.eventoo.mongodb.factory.MongoConnectionManager;

/**
 * Implementation Dao for credentials settings
 *
 * @author lukasz
 */
public class SettingsDaoImpl extends DAO Settings, String implements SettingsDao {

    public SettingsDaoImpl() {
        super(Settings.class, MongoConnectionManager.instance().getDb());
    }

    @Override
    public void saveSettings(Settings settings) {
        save(settings);
    }

    @Override
    public Settings readSettings() {
        return ds.find(Settings.class).get();
    }

    @Override
    public boolean updateSettings(Settings settings) {
        UpdateOperations createUpdateOperations = ds.createUpdateOperations(Settings.class).set("interval_cron", settings.getInterval_cron()).set("time_difference_event", settings.getTime_difference_event());
        UpdateResults update = ds.update(ds.createQuery(Settings.class), createUpdateOperations);
        return update.getHadError();
    }
}

Reference : [1] Springbyexample.org Person DAO [2] Spring Framework 3.0 Docs DAO [3] Spring Framework 3.2 Docs MVC
[4] Pastebin Settings DAO Source
[5] Pastebin Settings Implementation DAO Source

SQL Joins Explain Diagram

I must say that this one diagram of SQL Joins is one of the most memorizing image about how joins in sql works. Enjoy :)

SQL Joins Explain

Reference :
[1] Codeproject.com Visual Representation of SQL Joins

MySQL Refresh processlist every second

Very useful piece of command line query which will help you to keep an eye on execution time of queries which are performed in your MySQL database. It helps me when I ask myself : 'Hm ... I am wondering if this query is now executed ... '. This question can be sometime annoying, so this is quite helpful adoption of mysqladmin tool.

mysqladmin -u root -p -i 1 processlist

-u your username
-p you be pleased to give database password
-i 1 interval which equals 1 second

Example output :

+----+------+-----------+----+---------+------+-------+------------------+
| Id | User | Host      | db | Command | Time | State | Info             |
+----+------+-----------+----+---------+------+-------+------------------+
| 43 | root | localhost |    | Query   | 0    |       | show processlist |
+----+------+-----------+----+---------+------+-------+------------------+

Reference : [1] Mysqladmin Tool Doc