Android database connection using greenDAO library

greenDAO : Android ORM (Object/Relational Mapping) for SQLite database.

In Android, while dealing with big data projects we may require storing data locally. So very first thing comes in mind is SQLite.

But it may be complex to write SQL query for each transaction and it can be time-consuming.

Here is a simple solution to deal with android local database, greenDAO.

greenDAO is an object/relational mapping (ORM) tool for Android. It offers an object-oriented interface to the relational database SQLite.

Simple Guide:

Here are quick steps to start using greenDAO in our Android projects.

Add below dependencies into build.gradle(Module: app) file

apply plugin: 'org.greenrobot.greendao'

dependencies {

compile 'org.greenrobot:greendao-generator:3.2.0'
compile 'org.greenrobot:greendao:3.2.0'

}

And below code in build.gradle(Project: projectName) file

buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath 'org.greenrobot:greendao-gradle-plugin:3.2.1'
    }
}

Let’s create a class which will handle the database creation, say DbMain.java. For better understanding, we will create a commonly used table, Users table.

public class DbMain {
    public static void main(String args[]) throws Exception {
        Schema schema = new Schema(1, 
                             "your_package_name_goes_here");

        Entity users = schema.addEntity("Users");
        users.addLongProperty("Id")
             .primaryKey()
             .autoincrement();
        users.addStringProperty("Name");
        users.addLongProperty("Phone").unique();

        DaoGenerator daoGenerator = new DaoGenerator();
        daoGenerator.generateAll(schema, "./app/src/main/java");
    }
}

Here, Schema class constructor has two parameters version and package_name. Whenever you change the database structure, add/delete/update table or table columns, you will need to increment the version by 1 and run this DbMain.java class.

 

How to create a table using greenDao?

Very simple, use Entity class, provide the table name in addEntity(table_name) method as a parameter, this will automatically create a table for you. Use the instance of it to add columns in the table. You can update it anytime, just remember to increment the version value by 1.

Entity users = schema.addEntity("Users");

The class DbMain.java not only creates a table but also it generates few more classes automatically.

  • DaoMaster.java: This class has the operations for the overall database. It is Auto Generated by greenDao and don’t edit this class.
  • DaoSession.java: This class creates a session for each table. It is Auto Generated by greenDao and don’t edit this class.
  • UsersDao.java: For each table, there is a separate Dao class which will operate only on the table. It is Auto Generated by greenDao and don’t edit this class.
  • Users.java: This is just a model class (POJO class), which helps to bind the data to operate on the table. It is Auto Generated by greenDao and don’t edit this class.

 

How to run the DbMain.java class?

Right click on DbMain.java class, click on Run “DbMain.main()” or simply press ctrl+shift+F10. By running this class means, recreating the data structure. Refer below screen shots for quick understanding.

android_db

android_db1

Now, whenever you click on Run button in the toolbar, you might end up with running DbMain.java class each time. You will need to change Run Configuration to run your application.

Go to Run —> Edit Configurations —> from left panel select Android App —> app folder —> click on Ok. That’s it!

android_db2

android_db3

Now click on Run button, you will be able to run your project’s default configuration.

Till now we just created an environment to play and now it’s time to play!

CURD using greenDao

Create a data entry in a table.

 DaoSession daoSession = AppController.getInstance()
                                      .getDaoMaster()
                                      .newSession();
 UsersDao usersDao = daoSession.getUsersDao();
 Users user = new Users();
 user.setName("Qice");                   
 user.setPhone(9000000000);
 usersDao.insert(user); //This will add a row in the Users table.

Update data entry in a table.

 DaoSession daoSession = AppController.getInstance().getDaoMaster().newSession();
 
 UsersDao usersDao = daoSession.getUsersDao();
 try{
     User> user = usersDao.queryBuilder()
                      .where(UsersDao.Properties.Id.eq(1))
                      .uniqueOrThrow();

     user.setName("Qice Technologies");
     user.setPhone(9000000001);
     usersDao.update(user); // this line will update the data

 } catch(Exception e) {
  //catch the exception, if there is no row available for the id.
 }

Read the data from a table.

 DaoSession daoSession = AppController.getInstance()
                                      .getDaoMaster()
                                      .newSession();
 UsersDao usersDao = daoSession.getUsersDao();

 List<Users> users =  usersDao.queryBuilder().list(); 

 // This line gets all the row from the table, 
 //you can add  where clause to add constraints.

Delete data entry from a table.

DaoSession daoSession = AppController.getInstance().getDaoMaster().newSession();
 
 UsersDao usersDao = daoSession.getUsersDao();
 try{
 User> user = usersDao.queryBuilder()
                      .where(UsersDao.Properties.Id.eq(1))
                      .uniqueOrThrow();

 usersDao.delete(user); //this line will delete the data entry for the id.

 } catch(Exception e) {
    // catch the exception, if there is no row available for the id.
 }

You can find a complete sample of the Android project using greenDao in our GitHub repository.