AndroidRecord is an open-source ORM library for Android applications.

It's heavily inspired by Active Record and aims to ease performing basic CRUD operations on a SQLite database. It depends on conventions, so it requires very little setup and configuration.

Getting Started

AndroidRecord is distributed as a library project (instead of a JAR) because it needs to hook into your app to do some of the things it does. So, to get started, first grab a copy of the code:

git clone [email protected]:lyudmil/androidrecord.git

Then, look up your favorite IDE's instructions on how to add a library project for Android apps and follow the process to add AndroidRecord. You should be all set after that.

Using AndroidRecord

Set up the database

To start using AndroidRecord within your project, you need to first create a database. To do that, run the following code in an activity of your choice (I suggest your root activity):

DatabaseManager databaseManager = new DatabaseManager(getApplicationContext());
databaseManager.bootStrapDatabase();

This does the following:

• Looks up the resource R.string.app_name (which you ought to already have defined), converts its name to its underscored version, and creates a database with that name unless it already exists. If it already exists, it just uses it.

• Checks to see if there are any migrations to run. More on that later.

Create your first model

AndroidRecord is based on the Active Record pattern, so every model class represents the table schema, while every instance of the class is mapped to a row in the database.

So, the first step is to create a class that extends ActiveRecordBase and define the fields that are going to go in the table:

public class Course extends ActiveRecordBase<Course> {

    public String name;	// All fields you wish to save to the database must be declared public
    public String description;

    // More code...
}

Then, you need to create the corresponding table in the database.

To do this, you have to create your first migration. Migrations are a way of versioning your database. They are SQL files in the assets/migrations path named as consecutive numbers (1.sql, 2.sql, 3.sql...) that run in order if needed. When you call databaseManager.bootStrapDatabase(), it checks the current database version against the highest migration number defined and runs any migrations in between. That way you can easily move your database forward as your app evolves.

So, we must create a table for the Course class we defined above. The suggested way of doing this is by first creating a unit test:

public class CourseTest extends ModelTestCase<Course> {	// ModelTestCase is a class provided in ActiveRecord

    public void testFirstMigrationCreatesCoursesTable() throws Exception {
        assertDatabaseTableCreated(Course.class, 1); // Check that migration 1.sql contains the SQL required to create a table for the Course class
    }
}

Run this test and it should fail, spitting out the required SQL. Create assets/migrations/1.sql and paste that SQL. Run the test again and it should pass. You're now all set to do CRUD operations on courses.

CRUD

Here's where this starts paying off...

Create

To insert a new model into the database, all you have to do is call the ActiveRecordBase.save() method on the instance you want. So, following our Course example, use the following code:

Course course = new Course();
course.name = "Artificial Intelligence";
course.save();

That's all.

Read

There are several ways to read the database. If you know the ID of the record you want to look up:

Course savedCourse = new Course().find(1);

If you want to get all the courses:

List<Course> all = new Course().all();

The first course that matches a particular where clause:

Course ai = new Course().find("name='Artificial Intelligence'");

All courses that match a particular where clause:

List<Course> duplicates = new Course().where("name='Artificial Intelligence'");

Pretty simple, right?

Update

Updating a record works the same way inserting does. ActiveRecord checks to see if the record has already been saved to the database and issues an update query instead of a create one if it has been. So, to update records, look them up, change them in your code, and call ActiveRecordBase.save() when you're done.

Delete

Couldn't be simpler:

course.destroy()

Any questions? Of course not.

Associations

One-to-many

One-to-many associations in ActiveRecord a bidirectional. So, let's say we wanted all of our courses to be taught by exactly one teacher. First, create the Teacher class and indicate that it's a one-to-many relationship:

public class Teacher extends ActiveRecordBase<Teacher> {
    public String name;
    public String title;

    @HasMany(name = "teacher", relatedType = Course.class)
    public ActiveCollection<Course> lectures;		// Use ActiveCollection for collections you want to persist
}

There are two pieces of information you need to provide to the @HasMany annotation:

• name: the name of the field on the class on the "many" side of the association (Course) that represents the current class (Teacher). So, we're saying that the teacher of a course is represented by the teacher field on the Course class.

• relatedType: which class is on the "many" side of the association.

We also need to modify the Course class:

public class Course extends ActiveRecordBase<Course> {
    // Previous field declarations

    @BelongsTo
    public Teacher teacher;

    // More code...
}

We also need to write another migration to add a column called teacher_id to the courses table (our unit test should tell us that). Then, we're all set. We can use the lectures field just like any other collection. The only gotcha is that the owner of a collection must be saved before any of the owned entities. So, if a Teacher hasn't been saved, you won't be able to save any of their Course's without AndroidRecord spitting out errors at you.

One-to-one

One-to-one relations are much simpler to implement. Simply add a @BelongsTo annotation to the field of the owning class and add a database column to represent the relation (like what we did above with courses). You're strongly encouraged to use a unit test as a guide so that you get all the SQL right. It's not complicated, but why would you waste brain cycles thinking about it?

One-to-many

AndroidRecord doesn't currently support one-to-many associations. If you need to have one, you need to model it explicitly. Create a model that has a one-to-many relationship to each side of the many-to-many association you want to implement. So, continuing our courses example, modeling student enrollments in courses:

public class Enrollment extends ActiveRecordBase<Enrollment> {

    @BelongsTo
    public Student student;

    @BelongsTo
    public Course course;
}

Then, you've reduced the many-to-many relationship to two one-to-many relationships.

There's much more to cover, but this should be a good start. If you need help, shoot me an email: [email protected]

Hope you find it useful! Happy coding!