Demonstration of valid and invalid uses of one-to-many relationship in ActiveAndroid.

ModelRelationshipTest.java

package com.activeandroid.test;

import com.activeandroid.Model;
import com.activeandroid.annotation.Column;
import com.activeandroid.annotation.Table;
import java.util.List;
import static junit.framework.Assert.assertEquals;

/**
 * Tests model relationships.
 */
public class ModelRelationshipTest extends ActiveAndroidTestCase {

	/**
	 * Correct use of the one-to-many relatinship support in AA.
	 */
	public void testOneToMany() {
		One one = new One();
		one.save();

		Many many1 = new Many();
		Many many2 = new Many();
		many1.setOne(one);
		many2.setOne(one);

		many1.save();
		many2.save();

		List<Many> manyList = one.many();

		assertEquals(2, manyList.size());
	}

	/**
	 * Invalid use - collection change does not reflect back!
	 */
	public void testOneToManyInvalidUseCollection() {
		One one = new One();
		one.save();

		Many many = new Many();
		many.save();

		// this will not work the way you expect!!
		// result of many() is a list returned from a query,
		// changes to it are not reflected back to the database!
		one.many().add(many);
		one.save();

		List<Many> manyList = one.many();

		//now you could expect the Many instance to be in the collection, but in fact, it's empty
		//as the collection is just a one-way trip.
		assertEquals(1, manyList.size());
	}

	/**
	 * Invalid use - querying for related models on an unsaved model does not
	 * make sense.
	 */
	public void testOneToManyInvalidUnsaved() {
		One one = new One();
		//one.save(); //if you uncomment this, the test will pass

		Many many1 = new Many();
		Many many2 = new Many();
		many1.setOne(one);
		many2.setOne(one);

		many1.save();
		many2.save();

		one.many(); //there will be a NPE here, because one.getId() returns null
	}
	
	@Table(name = "One")
	public static class One extends Model {
		public List<Many> many() {
			return getMany(Many.class, "OneFK");
		}
	}

	@Table(name = "Many")
	public static class Many extends Model {

		@Column(name = "OneFK")
		private One one;

		public One getOne() {
			return one;
		}

		public void setOne(One one) {
			this.one = one;
		}
	}
}